CA1077734A - Method for controlling the relative stem growth of plants - Google Patents

Abstract

A B S T R A C T
A method for controlling the relative stem growth of plants by applying to the foliage of the plants, or to soil containing seeds of the plants, a plant-growth-regulat-ing amount of an imidazoisoindoledione or dihydroimidazoiso-indoledione or an optical or stereo isomer thereof.

Description

~077734 The invention relates to a method ~or controlling plant growth comprising treating the plants with a compound of the fonmula:
y H

X ~ ~ N ~ o Rl ~ ~ N ~ R

(I) ~II) whexein X represents H, CH3, Cl, OCH3, SCH3 or N02; Rl and R2 each represent alkyl Cl C4, provided that the sum of the carbon atoms in the groups represented by said Rl and R2 is 4 to 7, and when Rl and R2 are taken together with the carbon to which they are attached, they may represent cycloalkyl C5-C6 optionally substituted with CH3; and Y is hydrogen, including the optical and stereoisomers thereof. The compound may be applied to the foliage of the plant or to soil containing seeds of the plant.
In one aspect, the invention provides a method for controlling the relative stem growth of plants comprising treating the plants with a compound of the formula:

~ I N- ~ ~ R1 or ~ N ~f,o ~I3 (II) .~
~herein X represents H, CH3, Cls OCH3~ SCH3 or N02; Rl 2 alkyl Cl-C4, provided that the sum of the carbon atoms in the groups re-presented by said Rl and R2 is 4 to 7~ and when Rl and R2 are taken together with the carbon to which they are attached, they may represent cycloalkyl C5-C6 optionally substituted with CH3; and Y is hydrogen, including the optical and stereoisomers thereof; in an amount sufficient to increase or reduce the relative stem length o the treated plant.

~L~177734 In another aspect, the invention provides a method for inhibiting bud growth on plants comprising, contacting the plants with a bud growth inhi~iting amount o~ a compound of the formula:
Y` H
/ N ~ / O ~ I/N

N

(Il (II~

wherein X represents H, CH33 Cl~ OCH3, SCH3 or N02; Rl and R2 each represent alkyl Cl~C4, provided that the sum of the carbon atoms in the groups re-~esented by Rl and R2 i5 5 to 7, a~d when Rl and R2 are taken together with the carbon atom to which they are attachedJ they may represent cycloalkyl C5-C6 optionally substituted with methyl; Y is hydrogen; and the optical and stereoisomers thereof.
Preferred compounds for use as plant growth regulators are re-p~esented by formulas I and II above, wherein X is H, Cl9 CH3 or -SGH3; Y
is hydrogen; and Rl and R2 are alkyl Cl~C4 provided that the sum of the carbon atoms represented thereby is 4 or 5, or when Rl and R2 are taken together with the carbon to which they are attached they represent cycloalkyl C5-C6, The compounds of the pTeSent invention aTe highly effective plant growth regulating agents. They may be used effectively for controlllng the relative ste~ growth o both monocotyledonous and dicotyledonous plants by 2Q application thereof to the foliage of the plants, or by application to soil containing seeds of the plants. Generally, one treat~ent is effective on the total growth of the plant; however, repeated treatments are frequently ~ound to increase the ~la~

7~73~

1 extent of the effe t. The most characteristic growth altera-tions brought about by the treatment ~using formula I or II
compounds where X is a substituent other than chloro) are shorter, thicker stems, reduction in tillering and reduction in sucker growth. As such, the compounds of this invention (as defined above) are found to be particularly useful for treating roadside plantings, where it is desirable to reduce the number of grass cuttings and shrub prunings needed for proper grooming during the growing season. These compounds are also useful for dwarfing cereal grains such as rice, barley and wheat, and preventing lodging thereof. Usually, about 0.25 to 4.0 pounds per acre or 0.28 to 4.48 kg/hectare, and preferably 1.12 to 4.48 kg/hectare of the active compound is effective for achieving this dwarfing effect for compounds wherein Rl and R2 represent C5-C6 cycloalkyl or 0.28 to 1.2 kg/hectare where Rl and R2 are alkyl and have a total of 4 to 5 carbon atoms.
Surprisingly, it has also been found that certain of the compounds of this invention, particularly those of formula I, wherein X is Cl and Rl and R2 each represent alkyl Cl-C4, provided that the sum of the carbon atoms represented by Rl and R2 is 5 to 7, or when Rl and R2 taken together with the carbon to which they are attachedl represent cyclo~
alkyl C5-C6; induce a pronounced increase in relative stem length and/or foliage weight of plants, particularly dicotyl-edonous plants, when applied at rates of from about 0.25 to 10 pounds per acre or from 0.28 to 11.2 kg/hectare, either to the foliage of plants or to soil containing seeds thereof.
These compounds thus find utility as growth enhancing agents for crops, particularly broadleaf crops such as sorghum, soy-beans, cotton, cucumbers, snapbeans and peanuts. It i5, how-ever, also found that these compounds are useful for enhanc-ing the growth rate of corn.

7~773~

1 The plant growth regulating effects of the com-pounds of the present invention are further demonstrated by the compounds' usefulness for controlling sucker growth on mechanically topped tobacco plants. With the compounds of this invention, it is found that solutions and/or suspensions, preferably aqueous, containing from about 200 to 2000 ppm, and preferably 200 to 1000 ppm, of acti~e compound is effec-tive for inhibiting sucker growth on mechanically topped tobacco plants.
In tob~cco farming, bud growth is conventionally controlled by two mechanical processing operations. Plant height is regulated by cutting off the terminal bud flower of the tobacco plant in a process known as "topping." This process facilitates the development of the large leaf which forms the commercial crop. Their development i9, however, offset by the enhanced development of lateral (axillary) buds.
The lateral growth ~called "sucker growth") again reduces the nutrient supply available for large leaf development.
This necessitates a second mechanical operation: namely, the hand removal of the suckers from each tobacco plant. In the practice of the present invention, the inconvenient and ex-pensive mechanical steps can be avoided by two spraying opera-~ions. Firstly, terminal bud development can be controlled by an over-spraying of the active ingredient. Secondly, sucker development can be controlled by a subsequent spray-ing of the plant stem and foliage.
Harvesting of the marketable or prime leaves of flue-cured tobacco is usually begun about one to two weeks after treatment and may continue for four or five weeks.
Usually the leaves are cut from the bottom of the stalk in groups of three at weekly intervals. Inhibiting growth of axillary buds on topped burley tobacco is also important from the standpoint of improving quality and yielcl of tobacco, ~7773~a 1 although the harvesting procedure is somewhat different.
Accordingly, after the burley tobacco is topped, it is spray ed with a solution of the active materia;L to inhibit axillary bud development, and the whole stalk is lhen harvested in accordance with standard practices some iEive to ten weeks after treatment.
InaSmuch as the compounds of this invention are only very slightly water soluble, they are generally formu-lated for foliar treatments as wettable powders or flowable liquids which are usually dispersed in water or other inex-pensive liquid diluent for application to said foliage as a liquid spray. However, when said compounds are to be used where soil treatments are involved, the compounds of the invention may also be prepared as granular products.
A typical wettable powder can be prepared by grind-ing together approximately 46~ by weight of a finely divided carrier such as attapulgite, 50% by weight of the imid~zo-isoindoledione or dihydroimidazoisoindoledione of this inven-tion, 3% by weight of the sodium salt of condensed naphthalene sulfonic acids and 1~ by weight of sodium N-methylN-oleoyltau-rate.
A typical flowable liquid can be prepared by admix-ing about 42% by weight of the imidazoisoindoledione or dihy-droimidazoisoindoledione, with about 3% by weight of the sodium salt of condensed naphthalene sulfonic acids, 2~ by weight of finely divided bentoni~e and 53% by weight of water.
~ granular product can be prepared by dissolving the imidazoisoindoledione or dihydroimidazoisoindoledione in methylene chloride and spraying the thus-prepared solu-tion on a granular carrier such as sand, silica, kaolin,corn cob grits~ attapulgite, or the li~e.

; In accordance with this invention, formula I imid-azoisoindolediones can be prepared by cyclization of a phthal-7~3~

1 imidocarboxamide or a dioxoisoindolineacetamide. Cyclization can be achieved by reacting the said phthalimido derivative or isoindolineacetamide with a strong base, at an elevated temperature in the presence of an organic solvent.
The cyclization reaction is preferably conducted ;`! at a temperature of from 80C to 150C in the presence of a base such as sodium or potassium hydroxide, or an acid catalyst such as an aromatic sulfonic acid and a solvent which will azeotrope with water, permitting virtually immed-iate removal thereof from the reaction mixture as it is formed.
Among the solvents which may be employed are tolu-ene, ben2ene, xylenes and cyclohexane.
Bases which may be used include alkali metal hydr-oxides, alkali metal hydridesr alkali metal oxides, tertiary amines such as diisopropyl ethylamine, 1,5-diazobicyclo-[3.4.0]nonene-5; 1,5-diazobicyclo[5.4.0]undecene-5; 1,4-dia~o-bicyclo[2.2.2]octane; tetramethylguanidine, potassium fluoride and quaternary ammonium hydroxides such as trimethylbenzyl ammonium hydroxide and strongly basic ion exchange resins.
Acidic reagents which may be employed include aro-matic sulfonic acids such as p-toluenesulfonic acid, ~-naph-thalenesulfonic acid, naphthalenedisulfonic acid, and the like.
; In many cases, the ring closure may also be ach-ieved by a simple pyrolysis of the phthalimidocarboxamide or dioxoisoindolineacetamide at a temperature between 80C
and 250C.
These reactions may be illustrated as follows:

`~ ~
~77~3~

,N C--CON112 X O
.- .

It should also be understood that, in the above `; reaction, when X is not hydrogen the product of the reaction is a mixture of the two isomeric compounds since cyc:Lization occurs at either imlde carbonyl group as illustrated below:

~

' :' ~ ~ ~ .
\ / ~ R1 + X R1 2 O

Furthermore, when Rl and R2 represent different groups, the carbon to which Rl and R2 are attached is an asymmetric center and the products (as well as their inter-mediates) exist in d- and 1- forms.
~ Formula I imidazoisoindolediones can also be pre-pared by cyclization of the appropriate alkyl N-(carbamoyl-; alkyl) phthalamate with an alkali metal hydride such as sod-ium or potassium hydride, in the presence of an inert organic solvent such as toluene, xylene or benzene at an elevated temperature of about 80C to 150C. This reaction may be illustrated, using NaH as representative of the alkali metal -- 6 ~

.

~ ~77734 1 hydride, as follows-! ~ C()~ lkyl C

~CO-NH-C-CONIIz ~J~N R2R
X o I

; wherein X, Rl and R2 are as described a~bove. This reaution - is especially useful for the preparation of imidazoisoindole-diones in which Rl and R2 represent bulky groups such as isopropyl or t-butyl groups.
Furthermore, as with the previously described method for the preparation of the formula I imidazoisoindolediones, when Rl and R2 represent different groups, the carbon atom to which they are attached is an asymmetric carbon atom.
Therefore, if one starts with an optically active intermed-iate such as a-aminocarbonitrile, a-aminocarboxylic acid or a-aminocarboxamide, the intermediate N-(carbamoylalkyl) phthalamate and the imidazoisoindoledione, thus prepared, are optically active Conversion of the imidazoisoindoledione (I) to the dihydroimidazoisoindoledione (II) is achieved by a reduction reaction. This reaction may be carried out with sodium boro-hydride or a catalyst such as platinum or palladium catalyst, preferably on a carbon, silica or alumina support. The cata-lytic reduction is generally conducted under superatmospheric pressure between about 10 psig and 150 psig at an elevated temperature between 80C and 150C.
When Rl and R2 re~resent different gr~ups on the formula II dihydroimidazoisoindolediones, cls and trans iso-mers (stereoisomers) are obtained and both isomers are foundto be biologically active.
This reaction may be graphically illustrated as follows:

:

~ 7~73~

, . . .
Il ~'1 N~~ll4 ~N~o ~ R R1 ~ ~ N ~ R

I II

The intermediate phthalimidocarboxamide or dioxo-isoindolineacetamide, which is essentiaL to the preparation of the formula I imidazoisoindolediones of the present inven-tion, can be prepared by reacting an appropriate disubstitut-ed ketone with ammonium chloride, sodium cyanide and ammonium hydroxide, to obtain the ~,a-disubstituted-a-aminocarboni-trile. This a-aminonitrile is then reacted with phthalic anhydride to give the corresponding phthalamic acid.
This reaction is carried out at temperatures from about 20C to 60C in an inert solvent such as ether, tetra-hydrofuran, chloroform, methylene chloride, ben~ene, toluene and the like. The thus-formed phthalamic acid is then cyc-lized to the corresponding phthalimldocarbonitrile by heating with a dehydrating agent such as acetic anhydride, acetyl chloride, thionyl chloride, or the like, at temperatures from about 0C to 100C. Hydration of the thus-formed phthalimido-carbonitrile is preferably carried out with a strong acid such as sulfuric acid, with or without the addition of a non--miscible solvent such as methylene chloride or chloroform and the like at temperatures from about -10C to ~30C.
These reactions are graphically illustrated by using the sub-stituted phthalic anhydride as an example, and includin~ the cyclization of the phthalimidocarboxamide to form the compounds of this invention, as follows:

- ~\
~lL(97773~

l Rl ~ 0 St~l) l. 1 ~ 2 ~: O
~\ COO~I
t~ I I o + Nll2-~-CN ~ X~ R1 R2 ~ CO NII-C-CN

Stel~ 2 2 ~Step 3 X~ N-C-CON112 Step 4 X---~N-C-CN

O
Step 5 n X ~) ( I ) wherein X, Rl and R2 are as described above.
Alternatively, the above-mentioned intermediate phthalimidocarboxamide may also be prepared by the reaction of phthalic anhydride with a substituted aminocarboxylic acid to obtain the phthalimidocarboxylic acid which is con-verted to the corresponding acid chloride using thionyl chloride. This reaction is generally conducted in the pres-ence of an inert organic solvent 5uch as toluene, benzene, or the like, at an elevated temperature. The acid chloride 30 i5 then readily converted to the intermediate phthalimido-carboxamide by reaction with ammonia. This reaction is generally conducted in the presence of a solvent such as tetrahydrofuran at a temperature between about -10C and ~.~7'~73~

1 +15C. This synthetic route, including the cycliæation of the phthalimido carboxamide, is illustrated as follows:

O O

X ~ ~ O + N112-C-COOII - ~ N-C-COOII

O X O

O O
10 ~ ~ N-C-CON112 ~ ~ N-C-COCl X O I X O

~ Rl ,, wherein X, Rl and R2 are as described above.
As previously indicated, formula I imidazoisoindole-~0 diones can also be prepared by cyclization of an alkyl N~
(carbamoylalkyl) phthalamate wit:h an alkali metal hydride. .
The intermediate a-aminocarboxamide required for the prepara-tion of the alkyl N-(carbamoylalkyl) phthalamate, which is represented by the formula:
~ COO-a1kyl C1-C4 `~ CoNll-c-coNll2 where Rl and R2 are as previously described, can be prepared by reacting an a-aminocarbonitrile with sulfuric acid at an elevated temperature. This carboxamide is then reacted with a 2-carboalkoxybenzoyl chloride to yield the alkyl N-(car-bamoylalkyl) phthalamate, referred to above. These reactions ~ . . . . .

77~

1 may be graphically illustrated as follows:

. . .

N112~ ('N ~ N112-(`-CON112 ~1 ~ CO0-alkyl C1-C~
N112-C-CONII + I 11 - /
R2 ~ ~C0Cl 1 ~ ~ N~ll ~ C00-alkyl Cl-C4 ,~ N R
~, ~ R2 1 `~' ~CONH-C-CONH2 () R2 ~his invention is further demonstrated by the ex-arnples set forth below.

Preparation of 3-Isobutyl-3-methyl-5H-imidazo[2,1-a]-iso-indole-2t3H),5-dione A solution of 130.1 g (0.5 mole of a-isopropyl-a-methyl-1,3-dioxo-~-isoindolineacetamide in 650 ml toluene is heated with vigorous stirring under a Dean-Stark water separator in order to remove traces of water. The solution was cooled to 100C and 2.0 ~ sodium hydroxide in the form of pels i5 added and the mixture rapidly heated to reflux.
Water collects in the water separator. One-half hour after the addition of the sodium hydroxide, a further 2 g is added and heating is continued for a further 1 1~4 hours when no further water is removed from the reaction mixture and the infrared spectrum of an aliquot indicates the reaction to be complete. The reaction mixture is cooled to room temper-ature, fil~ered and the solids washed with toluene and the toluene removed in vacuo to leave a white solid which is trans-ferred to a filter funnel with hexane and air-dried to giv~

:~L¢i7~73~

1 98.7 g. of 2,5-dihydro-3-isopropyl-3-methyl-3H-imidazo[2,1-a]-isoindole-2,5-dione, melting point 93-96C. The product may be purified by recrystallization from hexane to give an ana-lytically pure sample, melting point 98-100.5C.
Alternatively, the product may be isolated by adding a slight excess of glacial acetic acid over the amount of sodium hydroxide used to the toluene reaction mixture, adding water, separating the or~anic phase, washing the organic phase with water, separating the organic phase, drying the organic phase, and finally removing the solvent to yield the product.
The above procedure is repeated in all respects, excepting that the strong base reagent is altered. In sepa-rate experiments, sodium hydride, potassium hydroxide, barium oxide, diisopropylethylamine, 1,5-diazobicyclo[5.4.0]undicene~
5, tetramethylguanidine, tetramethylbenzyl ammonium hydroxide, Amberlite A21 (Rohm & Haas) strongly basic ion exchange resin and ~-toluenesulfonic acid, are substituted for sodium hydrox-ide and yield the desired 3-isopropyl-3-methyl-5H-imidazo-[2,1-a]isoindole-2(3H),5-dione. In practice of the above--described method, sodium hydroxide or sodium hydride in re-Eluxing toluene is preferred.
Using the procedure described above, but substitut-ing the appropriate phthalimidocarboxamide or dioxoisoindoline-acetamide for a-isopropyl-a-methyl-1,3-dioxo-2-isoindoline-acetamide, and the selected strong base and solvent for sod-ium hydroxide and ~oluene, yields the imidazoisoindoline-diones reported in Table I below. Table I also indicates the solvent and base used as well as the melting po:int of the compounds obtained. With regard to the compounds synthe-sized and reported in Table I, it should be understood that when Y~H the product is a mixture of two isomeric compounds, since cyclization occurs at both imidecarbonyl groups.

. ' 7773~

- 1 In some cases, as shown .in Table I, there are separated either by franctional crystallization or column chromatography. In the other cases, the mixture, indicated by a two-number prefix before the subst:ituent X is tested for biological activity.

~77~3~

: . ---," ~ m __ ~ .

,. .,, ~J U~ l , , O O . ~1 In O~
~ ~ L~ ~ cn oo ' ~ ~7 ~ ~1 ~ A . , .

~0 1 ~C X co ~ ~ ~r ~ ~ ~ ~ a~ ~
O
~_ _ _ _ _ h u) ~;: 1~ X :~ X
t~ O t~i t~ ~ n~ ~d ~d ~ ~ Z Z Z _ Z "' ~7~734 _ _ ~4 r_ . ~ ~t ob ~ ~ ~ ul O~
r~ ~ ~1 r-i , r-~ r-l ~ ri t~ l l U~ l l Lr~
,~ O O r~ co . ~ ~ .
a~ 1~ c~ ~ r~ rl u~o~
:~: r~ ~ ~ r~ ~ o~

;
r~) r~ r~
::C ::C X
~,1 C~ C~
::~ X 5 U~ L~ U~
r_ ~_ ~_ t`J ~) ~ ~ X X
,' :C ~, X ~ ~ ~
~ _~ _ ~ ~ ~ r~
.,1 r~ X ~:~:
~ lY ~ ~ ~

H r~ r~) , , ~ X l X l l l X
Ii ¢ 00 O ~ Cl~
r_ _ Q~ a~ a ~::
r--~r-~ r''/ r-l r-l r-~ r-~
O O O O O O O
u~ E- E- E- ~_ ~_ E-_ _ _ _ ~ a~
~-I h U~ ~ ~C X ~ I~:C
t~O~ ~d ~d t~ tl~ ~d t~
~ ~ Z ~. ~; Z Z Z
~ __ _ ~ .

-Preparation of 3-~E~-Butyl-3-methyl-5H-imidazo[2,1 isoindole-2(3H),5-dione.

S ~ CH3 NaH ~
CO-NH-C-CONH2 ~ N CH3 : C~CH3)3 O C(CH3)3 A suspension of sodium hydride ~from 1.92 g of a 50% suspension of sodium hydride in mineral oil3 in 150 ml toluene is heated under reflux. During 20 minutes is then - added portionwise 6.13 g (0.02 mole) methyl N-(l-carbamoyl-1,2,2-trimethylpropyl)phthalamate to the stirred, refluxing, mixture. Heatlng is continued for 30 minutes after the addi-tion, the mixture filtered through diatomaceous earth, and the solvent removed in vacuo. The residue crystallizes and is recrystallized from a mixture of acetone-hexane to give 3-t-butyl-3-methyl-SH-imidazo[2,1-a]isoindole-2(3H),5-dione, melting point 136.5-137.5C.
The 3,3-diisopropyl-SH-imidazo[2,1-a]isoindole-

2(3H),5-dione (melting point 146-148C) is prepared in the manner described above, excepting that the methyl ester of N-(l-carbamoyl-l-isopropyl-2-methylpropyl)phthalamic acid is substituted for methyl N-(l-carbamoyl-1,2,2-trimethyl-propyl)phthalamate9 in the above reaction.

_ _ Preparation of ro-3-isobutyl-3-methyl-5H-imida~o-;~
[2,1-_~isoindole-2(3H),5-dione.
H H
/~ \~ NaBH4 ,~ , ~ ~
I I
~ ~ N _ CH3 ~ ~ /N - -CH3 CH(CH3)2 H(CH3)2 3L~77734 To a stirred suspension of 10.4 g (0.274 mole) sodium borohydride in 164 ml absolute ethanol under nitrogen was added dropwise at 5C a solution of 133.9 g ~0.548 mole) o~ 2,5-dihydro-3-isopropyl-3-methyl-3H-imidazo[2,1-a]iso-indole-2,5-dione in 155 ml tetrahydrofu.ran. After the addi-tion, the mixture is stirred a further 3 hours at room tem-perature and then poured over lQ70 g ice with stirring. The mixture is acidified with concentrated HCl and after stir-ring for 1.5 hours, the precipitate removed by filtration, washed with water and air-dried to give 11~.7 g of 1,9b-dihydro-3-isopropyl-3-methyl-5H-imidazo[2,1-a]isoindole-2t3H),5-dione, melting point 178-200C.
This compound is a mixtur0 of stereoisomers which can be graphically represented as follows:
}I H H H

CH(CH3)2 ~ CH3 O CH3 O CH~CH3)2 These isomers may be separated by fractional crystallization ~rom acetonitrile to give the less soluble isomer, melting point 234-236C and the more soluble isomer 9 melting point 217-221C, which are readily distinguishable by their nmr spectra. It is also understood that each of these stereo-isomers exists as a pair of optical isomers by virtue of theasymmetric carbon atom bearing the methyl and isopropyl groups.
The reductlon can be carried out in lower alkyl alcohols with or without the addition of water at tempera-tures pre~erably between 0C to 25C. Other reducing agents such as sodium cyanoborohydride and lithium borohydride may be used to effect this transformation.

7773~
, The following compounds lis~ed in Table II below are prepared essentially by the procedure described above, but substituting the appropriate imidazoisoindoledione for

3-isopropyl-3-methyl-5H-imidazo[2,1-a]isoindole-2(3H),5-S dione, in said procedure. The broad melting points shownin Table II reflect the fact that ~he compounds are mixtures of cis and trans isomers when Rl~R2 and that each stereo-isomer is a mixture of positional isomers with respect to X
when X~H.
' " ' .

.

.'' ' ~ .

, .' . .
: 25 :` :

~77~734 ~ ,, ----o ~ ~o o oo o~
,~ o ~ ~ ~n ~ o oc,~

~X
r . ~7773~

~ ~ ~ _ U~ ............ ~ ~ . ' .,, ~: t~, ~ ~ ~ ~ l l l ~1 0 0 O O l ~n u~ O
a~ ~ ~ o oo ~ ~t ~
~ ~ t~, ~ ,, ,, ~
_ o ~ u~ u~Ln n X ~
U ,_,_ ,_ , ~ ~, ~, ~_ ~ ~:~ X~ X~ X~ l l ,i ' H C_~ C~ ~ U ~

X X a~ ~o ~ cn c~ :~
,.._ _ _ ~ _ ~17773~

- Pour-Step Synthesis for the Preparation of Phthalimido-carboxamide Derivatives Essential for the Preparation of :
.~ Formula I, Imidazoisoindolediones.
- 5 Step 1. PreParation of the ~-Aminonitrile.
The following is a typical procedure:

2 5 ~o + NH4Cl + NaCN + NH40H - C2H5 CN

To a mixture containing 79 g (1.477 mole) ammonium chloride and 61.36 g (1.25 mole) sodium cyanide in 400 ml 28%
ammonium hydroxide solution is added dropwise with stirring and cooling 86.1 g (1 mole) diethylketone. After stirring overnight, the organic phase is separated and the aqueous phase extracted twice with methylene chloride. The organic phase and extracts are combined, washed with water and dried.
The drying agent is removed and the solvent removed in vacuo to leave essentially pure 2-amino-2-ethylbutyronitrile, as shown by the absence of a carbonyl band ~1700-1720 cm 1) in the infrared spec~rum. The aminonitriles can be purified if contaminated with starting ketone by dissolving the crude product in ether, adding anhydrous hydrogen chloride and collecting the precipitated hydrochloride salt. The free aminonitrile can then be regenerated by distributing the salt between methylene chloride and aqueous sodium bicarbon-ate solution, washing the organic phase with water, drying the organic phase and finally removing the solvent in vacuo.
Using this procedure, the following aminonitriles, reported in Table III below, are prepared as oils and char-acterized only by their infrared spectra.

TABLE III

Starting Ketone > ~ _ ~minonitrile X NH2 Rl Rl CN

~ ~
, CH 2 CH 2 - Cl~ 2 - CH 2 -. -CH3 -C(CH3)3 -CH3 CHtCH3)(C2H5) -CH(CH3)2 -CH(CH3)2 tCH2~5 (CH2)4 ~1 .
:

~7~773gL

`~Step 2. Preparation of the Phthalamic Acids.
The ollowing is a typical procedure:
~'' O

3~C ~ 2 ~ ~ ~ O
(CH3)2CH ~ CN ~\

~COOH

~ ~CO-NH-C-CN
CH~CH3)2 To a stirred boiling mixture of 28.1 g (0.189 mole) of phthalic anhydride in 28 ml methylene chloride is added dropwise 23.6 g ~0.21 mole) of 2-amino-2,3-dimethylbutyro-nitrile in 57 ml methylene chloride. After the addition, heating is continued for 3 hsurs. The mixture is cooled and the precipitate removed by filtration, washed with methylene chloride and air-dried to give 44.2 g (90%) of N-~l-cyano-192-dimethylpropyl)phthalamic acid, melting point 154-155C.
Other solvents such as ether, tetrahydrofuran, chloroform, benzene and toluene may be used in place of methylene chloride. The reaction can be run at temperatures from 0-100C, but preferably at 20-50C.
The phthalamic acids of Table IV are prepared by the general method described above using the appropriate phthalic anhydride and appropriate aminonitrile.

, . . . . .

~377734 .` ~ ~ ." _ , ,~ ~ ~ U~ ~ .i ~.,, ~, l l l Z
¢~

~C ~ ~
L~
. . :C x ~

.

~7773~L

Step 3. Preparation of the Phtha]imide Nitriles The following is a typical procedure:
o ~ COOH /~^~_,-C CH
1 Ir C,H3 ~ \N-C-CN
CO-NH-C-CN ~\ ~ ,C, CH(C~3)2 CH(CH3)2 o A suspension of 26 g ~0.1 mole) of N-(l-cyano-1,2-dimethylpropyl)phthalamic acid in 130 ml methylene chloride is heated with stirring under reflux. Thionyl chlo-ride (8.7 ml, 0.12 mole) is added dropwise, and after the addi-tion, the mixture heated for a further 3 hours. A further 5.8 ml (0.08 mole) thionyl chloride is added and heating con-tinued for a further 2.5 hours. The mixture is cooled down~
filtered and the solvent removed in vacuo leaving the product as a pale yellow oil which can be crystallized from ether-hexane, melting point 4B-51C.
Other solvents such as chloroform, benzene, toluene, ethylene dichloride, and th0 like, can be used in place of methylene chloride. Other reagents such as acetic anhydride and acetyl chloride may be used in place of thionyl chloride, and the temperature employed can vary from about 10-130C.
The following Table V lis~s the phthalimido-nitriles prepared by essentially the above procedure.

:: :

~: `
: ~377~73~

TABLE V

5~ Rl lN-C-CN

4 ~ R 2 . 5 X O

i: __ . ... . . . . __ .: Melting X _ 1 _ 2 _ _ Po in t , H -CH3 CH(C2H5) 2 oil . ~ _ . ._ . . _ l H -CH3 -CH~CH3) (C2H5) oi:L
,,` . _ . . . _ _ H -CH-CH2-CH2-CH2-CH2- 86-87. S :
:' . . ---- 1- ---- _ - CH3 ¦ - CH ~C 2H5 ) 2 . __ . .

..... ..
.; .

~1 .

~, .
, ~' ' 25 .

.

. ' .

.~, :

.. . .
.

~L~37~3~

Step 4. Yre~aration of thc Phthalimidocarboxamides.
. .
The following is a typical procedure:
O O
~ ,CH3 ~ ~ CH3 ~ N-C-CN l Il N-C-CONH2 \/~1/ C~l~CH3)2 ~ CH~CH3)2 To 404 ml o 85~ sulfuric acid is added, ~ith stirring and cooling to maintain a temperature of 14-16C, 242.3 g ~-isopropyl-~-methyl-1,3-dioxo-2-isoindolineaceto-nitrile in 67 ml methylene chloride. After the addition (2 hours~, the cooling bath is removed and the mixture stir-red a further 2 hours at room temperature. The reaction mixture is then poured into a stirred mixture o~ 2 1 water and 300 ml toluene. After 1 hour, the crystalline solid is removed by filtration, washed thoroughly with water, sus-pended in aqueous sodium bicarbonate solution and again filtered. After washing the solid with water, the product9 ~-isopropyl-~-methyl-1,3-dioxo-2-isoindolineacetamide, is air-dried and has melting point 165-166.5C.
The concentration of the sulfuric acid may be varied from about 70-100%, and the temperature from about 0-50C.
Co-solvents such as chloroform, ethylenedichloride, may also be used.
The compounds listed in Table VI below are prepared using essentially the same method described above.

- . ::

~C37773~

` TABLE VI
o s ~ R

~ ~2 S X O

__ _ Melting X Rl R2 Point .... .. _ H -CH3 CHtCH3)(C2H5) 129-135 . _ H -CH-CH2-CH2-c~2-cH2- 204.5-205.5 . ._ _ .. _ .
_ _ -CH3 C~ltC2H5)2 122.5-124.5 ~L~7773~

EXAMI'II` 5 Alternate T_ree-Step Synthesis for the Preparation of Phthalimidocarboxamides Essential for the Preparation of Formula I, Imidazoisoindolediones.
_.___ Step 1. Preparation o-f the Phthalimidocarboxylic Acids.
The following procedure is typical:
: O O

COOH
O O COOH
A mixture of 444 g ~3 mole) phthalic anhydride, 430 g (3.0 mole) l-aminocyclohexanecarboxylic acid and 39 ml triethylamine in 4.5 1 toluene is heated under reflux with stirring under a Dean-Stark water separator for 21 hours.
During this time, 54 ml water is collected. The mixture is slowly cooled to room temperature during which time the product crystallizes from the solution. The product, 1-phthalimidocyclohexanecarboxylic acid, 576.4 g, melting point 176-178C, is collected, washed with toluene and air-dried.
Other solvents such as acetic acid, benzene, dimethylformamide, xylenes and the like, as well as direct ;; fusion of the two reactants can be used to effect this - reaction at temperatures from about 50-250C.
The following compounds lis~ed in Table VII are prepared by essentially the same procedure using the appro-priate amino acid and phthalic anhydride.

.

. : , - ~7773~

TABLE VII
O

N-C-COOH
~ 2 X O

. ~ _ _ Melting X Rl R2 C
. .. _ .__ H -CH3 -C~2cH(cH3)2 133-135 .. _. . . . .. _ . ~
3-Cl _ _ _ ~ _ 193-194 Step 2. Preparation of the Phthalimidocarbo~y__C ~ rides.
The following procedure is typical:
O
~ 0 ' SOC12 O COOH

2 0 ~N~
O COCl A stirred slurry of 300 g (1.1 mole) l-phthalimido-cyclohexanecarboxylic acid in 2.5 l benzene containing 96 ml (157 g, 1.32 mole) thionyl chloride is heated under reflux for 3.25 hours. The solution is then cooled, filtered and the solvent removed in vacuo to leave the l-phthalimidocyclo-hexanecarbonyl chloride as an oil, characterized only by its infrared spectrum and used directly for Step 4, described below.
Other solvents such as chloroform, methy:Lene chloride, dichloroethylene, toluene, xylene, and the like, may be used for this reaction at temperatures from about - 30 ~

.

~77734 20-100C. Also, other halogenating agents such as thionyl bromide, phosphorus oxychloride may be employed to prepare the reactive acyl halide.
The following compounds, listed in Table VIII and characterized only by their infrared spectra, are prepared by essentially the same procedure.
TABLE VIII

s ~ Rl l N-C-COCl 4 ~ R2 X O

_ X I. _ -CH3 ¦ CH2CH(CH3)2 lS 3-Cl ~CH?)5 Step 3. Preparation of the Phthalimidocarboxamides.
The following is a typical procedure:

~N~ NH3 .

ZS [~ ~
O CONH2 ~ .

The crude l-phthalimidocyclohexanecarbonyl chloride prepared above in Step 3 is dissolved in 3.5 1 tetrahydrofuran, and the solution cooled to 5C. Ammonia is then bubbled into the solution with stirring until infra-red analysis of the liquid phase indicates that a:ll the acid ~77734 chloride is converted to the amide. The reaction mixture is then poured into 8 1 of water with stirring, the product ; removed by filtration, washed with water and air-dried to - give 259.1 g of l-phthalimidocyclohexanecarboxamide, melting point 224-226C.
Other solvents such as dioxan, toluene and ether may be used instead of tetrahydrofuran at temperatures prefer-ably between 0-25C. When water-immiscible solvents are used, the organic phase must be separated, dried and the solvent removed in vacuo and the product crystallized from an appro-priate solvent.
The compounds listed in the following Table IX are prepared by essentially the same procedure.
TABLE IX
~ 15 6 ,, 5 ~ Rl -C-cONH2 ..... _ _ . ... _ Melting X - Rl - R2 _ Point H -CH3 -CH2CH(CH3)2 170-171 ; 3-Cl (CH2)5 193-194 Pre aration of Phthalamic Acid Esters which are Intermediates for the Preparation of Formula I? Imidazoisoindolediones.
Step 1. Preparation of_a-Aminocarboxamides.
The following procedure is typical:
H2NXCN H2NXcoNH2 H2S4 ~ 1 ~J 'J

.

~77734 To 20 g concentrated sulfuric acid at 5C is added with stirring 10 g of l-aminocyclohexanecarbonitrile. After the addition, the mixture is heated with stirring at 100C
for 1 hour. The hot solution is then poured onto ice, the solution made strongly basic with 50% aqueous sodium hydrox-ide solution, and extracted three times with chloroform. The extract is washed with water, saturated NaHCO3 solution, dried, and the solvent removed in vacuo to leave the product, l-aminocyclohexanecarboxamide, as a crystalline residue, melting point 99-102C. This can be recrystallized from either benzene or ether to give a pure product, melting point 101-102C.
The ~-aminocarboxamides listed in Table X below were prepared by essentially the procedure described above.
TABLE X
Rl~ C ~NH2 R2~ ~CONH2 . ... ..
Melting Rl R2Point -CH3_ _ 185-186 Step Z. Preparation of the Phthalamic Acid Esters.
The following is a typical procedure:

25~ COOCH3 /C \
COCl (CH3)3c CONH2 ~ CH3 ~ CONH C - CONH2 C(CH3)3 ~L~37~73~
:
To a stirred suspension of 16.3 g (0.113 mole) of 2-amino-2,3,3-trimethylbutyramide in 226 ml dry tetrahydro-furan containing 16.~ ml dry triethylamine at 5C is added - dropwise a solution containing 22.4 g (0.133 mole~ of 2-carbomethoxybenzoyl chloride [Rec. Trav. Chem. 92, 824 (1973)]
dissolved in 56 ml dry tetrahydrofuran. After the addition 9 the mixture is stirred at room temperature for 2 hours and then poured into 400 ml ice cold water. The product was extracted into ethyl acetate, the extract dried over sodium sulfate, the dryin~ agent removed by filtration, and the solvent removed in vacuo. The residual oil crystallizes and the product, methyl N-(l-carbamoyl-1,2,2-trimethylpropyl3-phthalamate, recrystallized from acetone-hexane, melting point 146-1~7C.
Other solvents such as ether, dioxane, benzene, toluene, methylene chloride, chloroform, and the like, may be used instead of tetrahydrofuran at temperatures from about 0-50C, but preferably at 5-25C.

.: .
Control of Axillary Tobacco Buds.
Seedling tobacco plants are transplanted into six-inch plastic pots containing a greenhouse soil mix (loam soil:
sand:muck, 1:1:1). The plants are grown in the greenhouse for eight to ten weeks and then topped just above the eleventh node. The active ingredients are applied as foliar sprays to the entire plant, immediently after topping. Each spray solu:
tion is prepared by dissolving the desired amount of active i~-gredient in an acetone-water mixture containing 0.5~ TWEEN 20, polyoxyethylene sorbitan monolaurate (Atlas Powder Company).
The plant to be sprayed is placed on a turntable and 40 ml of the spray solution applied to the plant from three directed nozzles. The concentration of active ingredient in the spray rr~ ~Q ~ ~RI~ _ 3 4 ~.~7773a~

solution is 200 pl)m and lOn() I)pm. AEter spraying, thc plants are placed at random Oll a greenhouse bench and watered normally for a period of two weeks. At the termi-nation of each test, the suckers are removed from all nodes, weighed and the results expressed as percent inhibition com-pared with the fresh weight of suckers from untreated con-trols. The results achieved are set Eorth in Table XI below.
Maleic hydrazide, a commercial bud growth regulant is in-cluded for comparison.
' ' ~77~73~L

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~7773~

Plant_Growth Regulatin~ Effect of Test Compounds_Applled-to the Foliage of Plants and to Soil Containing Seeds of Said Plants.
To evaluate test compounds as plant growth regu-lating agents, said compounds are dissolved or dispersed in 50/50 aqueous acetone mixtures and applied to the foliage of seedling plants and to seeded pots of test plant species.
:
The plant species used in these tests are as follows:
Plant Variety Fescue Kentucky-31 ; Sorghum W-55 Rice Nato Wheat Bonanza Barley Larker Corn XL-45 Soybean Adelphia Cotton Stoneville Cucumber ~arketer ; Snapbean Sprite Peanut NC-2 Sugarbeet Monogerm ~ Treatment consisted of spraying the test compound - 25 in acetone:water (1:1) at the rate of 86 gallons per acre with a moving nozzle on a stationary track. The spray nozzle moved at a constant speed over the test species.
In soil treatment tests, containers are filled to ; 30 ~ - 37 -7773~

within one inch of the top with greenhouse potting soil, tamped, seeds of test plant species placed on top of the soil, sprayed, then covered with additional potting soil.
The pots are watered immediately after treatment and benched at random in the greenhouse. Normal watering and fertilizing practices are followed. Minimum day and night temperatures of 65F are maintained during cooler portions of the year.
Normal daily temperature fluctuations occur during the summer season.
Foliage tests are conducted in the same manner described previously in the soil tests. However, the same plant species employed in this test are well established seedlings approximately 2 to 3 inches in height. Plants are watered prior to treatment and are sprayed to provide the same rate of 0.25 and 4 pounds per acre or 0.28 and 4.48 kg per hectare of test compound.
Data Recording _ _ _ _ _ Initial observations are made at three to five days after treatment for early germination of test species.
Morphological changes from the norm are noted during the test period. Final observations are made four weeks after treatment. At this time, measurements o~ the height of plants are made. From these measurements, increases or decreases as compared to control plants can be noted. Data obtained for both treatments (I = foliar and II = soil) are reported in Tables XII and XIII below.

~377~3~L
' Rating Scale:
. 1 - No effect 2 - Poor activ.ity .
. 3 - Fair activity . 5 4 - Good activity

5 - Excellent activity

6 - Toxic : - - Inhibition or dwarfing ~ D - Dead ~, ~' .

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1~77~934 EXAMPLE_9 Evaluation of Test Compounds as Plant Growth Re~ulating ~ents.
In -these tests, containers are prepared by putting 100 ml of soil (soil type described previously) in each 2 3/4 inch square plastic pot as a base, then three Amsoy soybean seeds are placed on this base and are covered with soil ~3/8 to 1/2 inch). Seeds of Kentucky 31 Fescue are separately mixed with soil and 50 ml of the soil-seed mix are added to the pot to provide each pot with approximately 625 fescue seeds.
To prepare the test compounds, 20 mg of the com-pound is placed into a two-ounce, wide-mouth glass bottle and dissolved or dispersed in a 50/50 acetone/water mixture sufficient to prepare a 1000 ppm solution or suspension.
An addition of 5 ml of the 1000 ppm solution in each cup is equivalent to 10 lbs/acre or 11.2 kg/hectare.
Just prior to the application of the compounds, the test pots are tamped to level the soil and are lightly watered to prevent formation of air pockets and channelling routes during application which would prevent even distribu-tion of the test compound in the 50il with a pipettor.Three replications are used for each compound.
Each test includes 5 ml of 1:1 acetone:water controls, 5 ml water controls as a standard for comparison of activity from test to test. The treated plants are benched in the greenhouse and normal watering practices are followed. Minimum day and night temperatures O:e 65F are maintained during cooler portions of the year. Normal daily temperature fluctuations occur during the summer season.
Data obtained are reported below in Table XIV.
Data Recording Initial observations are made at three to five days after treatment for early germination of both test - a6 -~a97773~

species. Physiological or morphological changes from the norm are noted during the test period. Final observations are made at two to three weeks after treatment ~dependent on time of year). At this time, measurements of the height of plants of both species are made. From these measurements, percent increases or decreases as comyared to control plants, are calculated.
~;~ From the data reported below, it can be seen that 211 compounds tested increased the height of soybean plants;
that with the exception of 7'(and 8')-methyl-spiro{cyclo-hexane-1,3'-~3H)imidazo[2,1-a]isoindole}-2',5'-dione; 9'-chloro-1',9'b-dihydro-spiro{cyclohexane-1,3'-(3H)imidazo-[2,1-a]isoindole}-2',5'-dione; and 9(or 6)-chloro-3-isobutyl-3-methyl-5H-imidazo[2,1-a]isoindole-2(3H),5-dione, all showed an increase in soybean plant weight; that 9'-chloro-spiro-{cyclohexane-1,3'-(3H)imidazo[2,1-a]isoindole}-2',5'-dione;
9(or 6)-chloro-3-isobutyl-3-methyl-5H-imidazo[2,1-a]isoindole-2(3H),5-dione and 9'-chloro-1',9'b-dihydro-spiro{cyclohexane-1,3'-(3H)imidazo[2,1-a]isoindole}-2',5'-dione, caused a pro-nounced increase in fescue weight and a weight increase, andthat the 7'(and 8')-methyl-spiro{cyclohexane-1,3'-(3H)imidazo-~2,1-a]isoindole}-2',5'-dione and 3-isobutyl-3-methyl-5H-imidazo[2,1-a]isoindole-2(3H),5-dione caused pronounced dwarfing of the fescue.

- ~7 -.. ..

- ^~
773~

T~BLE XIV
Plant Growth Regulatin~ Ef-ect of Test Compounds on Soybeans_and Fescue So bean Fescue Y _ _ Height Weight Height Weight Compound -- ~cm) (g) (cm) (g) ~~~
Untreated Controls 14.5 6.31 14.0 4.47 Average of Ten Replicates 9'-Chloro-spiro{cyclo- 25.0 7.2 24.0 6.1 hexane-1,3'-(3H)- 30.0 6.3 24.0 5.6 imidazo[2,1-a]iso- 23.0 7.6 26.0 5.0 indole}-2',5'-dione . .
9'-Chloro-l',9'b- 16.0 5.5 22.0 4.9 dihydro-spiro{cyclo- 17.0 6.8 22.0 5.2 hexane-1,3'-(3H~- 15.0 6.0 24.0 4.8 imidazo[2,1-a]lso-indole}-2',5~-dione 7'(and 8')- ethyl- 19.0 4.6 10.0 1.4 spiro{cyclohexane- 14.0 8.0 0.9 1,3'-(3H)imidazo- 14.0 9.0 1.2 [2,1-a~isoindole}-2',5'-dione 3-Isobutyl-3-methyl- 16.0 6.1 12.0 3.5 5H-imidazo[2~1-a]- 14.0 7.4 10.0 5.2 isoindole-2(3H),5- 16.0 6.9 14.0 3.8 dione 6'(and 9')-(Methyl- 15.0 6.5 14.U 3.7 thio)-spiro{cyclo- 18.0 6.8 12.0 2.8 hexane-1,3'-(3H~- 16.0 7.2 14.0 2.9 imidazo[2,1-a]-isoindole}-2',5'-dione 6'(or 9')-Chloro- 15.0 6.6 15.0 3.8 spiro{cyclopentane- 15.0 6.5 14.0 4.1 1,3'-(3H)imidazo- 17.0 6.4 16.0 2.7 [2,1-a]isoindole}-2',5'-dione 6(or 9)-Chloro-3- 15.0 6.6 16.0 4.5 isobutyl-3-methyl- 18.0 7.4 17.0 3.9 5H-imidazo[2,1-a]- 14.0 6.5 19.0 3.8 isoindole-2(3H),5-dione, (isomer 1) 9(or 6)-Chloro-3- 17.0 5.5 18.0 5.4 isobutyl-3-methyl- 17.0 6.3 18.0 5.9 511-imida7o[2,1-a]- 17.0 6.2 18.0 4.9 isoindole-2~3H),5-dione, (isomer 2) .. ~ .. _ __

Claims (15)

1. A method for controlling the relative stem growth of plants comprising treating the plants with a compound of the formula:

or (I) (II) wherein X represents H, CH3, Cl, OCH3, SCH3 or NO2; R1 and R2 each represent alkyl C1-C4, provided that the sum of the carbon atoms in the groups represented by said R1 and R2 is 4 to 7, and when R1 and R2 are taken together with the carbon to which they are attached, they may represent cycloalkyl C5-C6 optionally substituted with CH3; and Y is hydrogen, including the optical and stereoisomers thereof; in an amount sufficient to increase or reduce the relative stem length of the treated plant.

2. A method according to Claim 1, for increasing the relative stem growth of plants comprising, applying to the foliage of the plant or the soil in which it is growing, from about 1.12 to 11.2 kg/hectare of a compound , wherein X is chloro , R1 and R2 each re-present alkyl C1-C4 provided that the sum of the carbon atoms represented thereby is 5 to 7, or when R1 and R2 are taken together with the carbon to which they are attached represent cycloalkyl C5-C6.

3. A method according to Claim 2, wherein the compound has the formula:

wherein R1 and R2 each represent alkyl C1-C4, provided that the sum of the carbon atoms represented by R1 and R2 is 5 to 7, or when R1 and R2 are taken together with the carbon to which they are attached they represent cycloalkyl C5-C6.

4. A method according to Claim 2, wherein the compound is 9'-chloro-spiro{cyclohexane-1,3'-(3H)imidazo[2,1-a]-isoindole}-2',5'-dione.

5. A method according to Claim 2, wherein the compound is 6-chloro-spiro{cyclohexane-1,3'-(3H)imidazo-[2,1-a]isoindole}-2',5'-dione.

6. A method according to Claim 2 wherein the compound is 6(or 9)-chloro-3-isobutyl-3-methyl-5H-imidazo[2,1-a]isoindole-2(3H),5-dione.

7. A method according to Claim 1, for reducing the relative stem growth of plants comprising, applying to the foil-age of the plants or the soil in which it is growing, from about 0.28 to 4.48 kg/hectare of a formula I or formula II compound, wherein X is H, CH3, NO2, OCH3 or SCH3.

8. A method according to Claim 7, wherein the compound is 3-isopropyl-3-methyl-5H-imidazo[2,1-a]isoindole-2(3H),5-dione.

9. A method according to Claim 7, wherein the compound is spiro-{cyclohexane-1,3'-(3H)imidazo[2,1-a]-isoindole}-2',5'-dione.

10. A method according to Claim 7, wherein the compound is spiro-{cyclopentane-1,3'-(3H)imidazo[2,1-a]-isoindole}-2',5'-dione.

11. A method for inhibiting bud growth on plants comprising, contacting the plants with a bud growth inhibiting amount of a compound of the formula:

or (I) (II) wherein X represents H, CH3, Cl, OCH3, SCH3 or NO2; R1 and R2 each represent alkyl C1-C4, provided that the sum of the carbon atoms in the groups represented by R1 and R2 is 5 to 7, and when R1 and R2 are taken together with the carbon atom to which they are attached, they may represent cyclo-alkyl C5-C6 optionally substituted with methyl; Y is hydrogen;
and the optical and stereoisomers thereof.

12. A method according to Claim 11 for inhibiting axillary buds on tobacco plants comprising, applying to the plants a bud growth inhibiting amount of the compound.

13. A method according to Claim 12, wherein the compound is a formula I imidazoisoindoledione.

14. A method according to Claim 13, wherein the compound is spiro-(cyclohexane-1,3'-(3H)imidazo[2,1-a]-isoindole)-2',5'-dione.

15. A method for controlling plant growth comprising treating the plants with a compound of the formula:

or (I) (II) wherein X represents H, CH3, Cl, OCH3, SCH3, or NO2; R1 and R2 each represent alkyl C1-C4, provided that the sum of the carbon atoms in the groups re-presented by said R1 and R2 is 4 to 7, and when R1 and R2 are taken together with the carbon to which they are attached, they may represent cycloalkyl C5-C6 optionally substituted with CH3; and Y is hydrogen, including the optical and stereoisomers thereof.