CA1250843A - Quinoxaline and their production - Google Patents

Abstract

Abstract:
The present invention is directed to compounds of the formula:

wherein X is a hydrogen atom, a fluorine atom or a chlorine atom and A is a group of the formula: or

Description

Quinoxaline and Their Production The present application has been divided out of Canadian Patent Application Serial No. 492,126 filed October 3, 1985.
This invention rela-tes to novel quinoxalines, their production and use as intermediates in the preparation of tetrahydrophthalimides.
The invention provides compounds of the formula:

O=~

wherein X is a hydrogen atom, a fluorine atom or a chlorine atom and A is -fH-N- or -C=N- in which R is a hydrogen atom or a methyl group, R is a hydrogen atom or a methyl group and the nitrogen atom is bonded to the benzene ring.
Preferred among the compounds of formula tI) are those wherein X is a fluorine atom, particularly those wherein A is -CH2C_CH or -CH2CH=CH2.
These compounds are useful as intermediates in the preparation of tetrahydrophthalimides of the general formula:

~[~

wherein R is a Cl-C5 alkyl group, a C3-C5 alkenyl group, a C3-C5 alkynyl group or a Cl-C3 alkoxymethyl group and X and A
are as defined above.
The production of the quanoxaline (I) is summarized in the following scheme:

F ~ N ~ ) O I R ~ ) (IV) (V) ~N~/ ~¦ R2 I~--X~
O ~ N ~ ~ (R3 = H) H

(VII) (VI) (I) wherein X, R2 and R3 are each as defined above and R4 is a Cl-C4 alkyl group.
The above conversions will be explained further in detail below. Namely, the N-nitrophenylphthalimide (IV) is xeacted with an amino acid ester of the formula:

HN-CH-COOR (VIII) wherein R2, R3 and R4 are each as defined above in an amount of 2.5 to 4 equivalents to one equivalent of the N-nitro~
phenylphthalimide (IV) in a solvent (e.g. dioxane, dimethyl-formamide, dimethylsulfoxide) at a temperature of 50 to 200C to give the N-phenylamino acid ester (V).
The resultant N-phenylamino acid ester (V) is subjected to reductive cyclization with an appropriate reducing agent, for instance, iron in an acid (e.g. acetic acid) to give the dihydroquinoxalinone (VI). More specifically, the N-phenylamino acid ester (V) is ~reated with 3 to 10 equivalent amounts of powdery iron such as electrolytic iron or reduced iron in a solvent (e.g. water, alcohol, acetic acid, ethyl acetate) in the existence of an excessive amount of an acid (e.g. acetic acid, hydrochloric acid) at a temperarture of 50 to 200C.
The N-phenylamino acid ester (V) is novel, while the N-nitrophenylphthalimide (IV) is per se known and obtainable by the method as described in EP-A-0077938A.
Typical examples for production of the starting compounds (V) and (VI) are illustratively shown in the following Examples.
Example 1

2-(4-Fluoro-3-nitrophenyl)-4,5,6,7-tetrahydro-2H-isoindole-1,3-dione (5.8 g) was added to a mixture of glycine methyl ester hydrochloride (7.5 g), triethylamine (6 g~ and 1,4-dioxane (50 ml), and the resultant mixture was heated under reflux for 4 hours, followed by addition of water and extraction with ethyl acetate. The extract was washed with water, dried and concentrated. The residue was crystallized from methanol to give 2-(4-methoxycarbonyl-methylamino-3-nitrophenyl)-4,5,6,7-tetrahydro-2H-iso-indole-1,3~dione (2.6 g). m.p., 220C.

~5~3 In the same manner as abo~e, the M-phenylamino acid esters (V~ as shown in Table l were obtained:
Table 1 O R2 R3 X o R O-C~CH-N ~ ~ (V) Compound X R R3 R4 Physical constant No.
a F H H CH~CH3 m.p., 166.8C
b F H CH3 CH2CH3 m.p., 159.2C
c Cl H H CH2CH3 m.p., 153 - 154C

Example 2 2-(4-Methoxycarbonylmethylamino~3-nitrophenyl)-4,5,6,7-tetrahydro-2H-isoindole-1,3-dione (2.06 g) was dissolved in a mixture of acetic acid (20 ml) and ethyl acetate (20 ml), and the resultant solution was dropwise added to a mixture of 5 % aqueous acetic acid (lO ml) and iron powder (4 g) at 70 to 80C, followed by stirring at the same temperature for 3 hours. The reaction mixture was allowed to cool, diluted with water and extracted with ethyl acetate. The extract was washed with sodium bicarbonate solution, dried and concentrated to give 2-(3,4-dihydro-2(lH)-quinoxalinon-7-yl)-4,5,6,7-tetrahydro-2H-isoindole-lS 1,3-dione (1.3 g). m.p., 208 - 209~C.

In the same manner as above, the dihydroquino-xalinones ~VI) as shown in Table 2 were obtained.
Table 2 R

R2 ~ ~ (VI) o Compound X R R3 Physical constant No.
d H H CH3 m.p., 263.4C
e F H H m.p., 236.6C
f F CH3 H m.p., > 220C
g Cl H H m.p.~ 174C

Example 3 2 ~3,4-Dihydro-6-_luoro-2(lH)-quinoxalinon-7-yl)-5 4,5,6,7-tetrahydro-2H-isoindole-1,3-dione (0.43 g) was added to a mixture of sodium hydroxide ~0.16 g), water (2.1 ml) and 30 % aqueous hydrogen peroxide ~0.21 ml), and the resultant mixture was stirred at room temperature for 16 hours. Ether was added thereto to separate an aqueous layer, which was adjusted to pH 4 with acetic acid. The precipitated crystals were collected by filtration and washed with water to give 2-(6-fluoro-2~lH)-quinoxalinon-7-yl)-4,5,6,7-tetrahydro~2H-isoindole-1,3~dione (0.32 g).
m . p . , ? 300C.

The tetrahydrophthalimldes can be obtained by reacting a quinoxaline of the formula:

o ~X/~o H

wherein X and A are each as defined above,with a halide of the formula:
R1_y (III) wherein Rl is as defined above and Y is a chlorine atom, a bromine atom or an iodine atom in a solvent in the presence of a dehydrohalogenating agent at a temperature of 0 to 50C
for a period of 0.5 to 24 hours.
In the akove reaction, the halide (III) and the dehydro-halogenating agent are used respectively in amounts of 1 to 3 equivalents per equivalent of the quinoxaline (I). Examples of the solvent are ethers (e.g. diethyl ether, diisopropyl ether, dioxane, tetrahydrofuran, ethylene glycol, dimethyl ether~, acid amides (e.g~
formamide, N,N~dimethylformamide, N,N-dimethylacetamide), sulfur compounds (e.g. dimethylsulfoxide), and their mixtures. Inorganic bases (e.g. sodium hydride), organic lithium compounds ~e.g. n-butyl lithium, methyl lithium, lithium diisopropylamide), etc. may be used as the dehydro-halogenating agent.
After completion of the reaction, the reaction mixture is subjected to an ordinary post-treatment such as extraction with an organic solvent and concentration. If desired, any conventional purification procedure, such as recrystalli~ation or chromatography, may be employed.
Practical and presently preferred embodiments for the production of the tetrahydrophthalimides are illustratively shown in the following Examples.
Example 4 Sodium hydride (33 mg) was suspended in N,N~
dimethylformamide (1.5 ml), and the resultant suspension was cooled to -30C. 2-(3,4-Dihydro-6-fluoro-2(1H)-quinoxalin-7-yl)-4,5,6,7-tetrahydro-2H-isoindole-1~3-dione (400 mg) was added thereto at -30C, followed by stirring for 30 minutes.
l-Bromo-2-propyne (165 mg) was added thereto at -30C, and the temperature was gradually raised to room temperature (e.g. 20 - 25C~, followed by stirring for 6 hours. The reaction mixture was admixed with water and extracted with ethyl acetate. The extract was washed with water, dried and concentrated. The residue was purified by silica gel thin layer chromatography using a mixture of ethyl acetate and hexane (1 : 2) as an eluant to give 2 [3,4-dihydro-6-fluoro-1-(2-propionyl)-2(1H)-quinoxalinon-7-yl]-4,5,6 7-tetrahydro-2H-isoindole-1,3-dione (80 mg). m.p., 205.6C.
The tetrahydrophthalimides as shown in Table

3 were obtained in the same manner as above.

~ o o o o o o o ~ ~
~1 ~ J ~I r-/l ~ N ~

r~ ~ ~ ~
~1 U~ U D N

I ~ 1 X ::C X ~

. I I I I Z Z-~ Z ~ I

Q~ Z'P~ X ~
E~ O ~

O ,~ ~ ~ ~ In ~D r~ co cr~
UZ

. U C~
~D oO
~ 00 ~ ~ O ~D
~ ~ ~ oc~ o C,) ~
_ o ~, CO ~ ~ o U~ o U~ o ~ o U ,~
,, ..
o O s ~ ~ ~ e rl ~

~ V
P;

C~

~ u U--C~ m 3~ ~ 3 ~ ~ 1I N I N

X ~ 4 .

~ o ~ ~ ~ ~ O ~1 U _ _ ~ lu ~ ,~
c~ ~

~ c~ ~
p~ ~
c~

x ~a zl z~ z~ zl ~ c~

x :~

O ~ ~
o o ~
c~ z It has been found that the tetrahydrophthalimides show a high herbicidal activity against a wide variety of weeds including broad-leaved weeds, Graminacaeous weeds, Commelinaceous weeds and Cyperaceous weeds in agricultural plowed field by foliar or soil treatment without producing any material phytotoxicity in various agricultural crops such as corn, wheat, rice, soybean or cotton. Exam-ples of broad-leaved weeds are wild buckwheat (Polygonum convolvulus), pale smartweed ~Polygonum lapathifoliu~
lC common purslane (Portulaca oleracea), common chickweed (Stellaria media), common lambsquarters (Chenopodium album), redroot pigweed (Amaranthus retroflexus), radish (Raphanus sativus), wild mustard (Sinapis arvensis), hemp sesbania (Sesbania exaltata), sicklepod (Cassia obtusifolia), 15 velvetleaf (Abutilon theophrasti), prickly sida (Sida spinosa), field pansy (Viola arvensis), catchweed bedstraw (Galium aparine), ivyleaf morningglory (Ipomoea hederacea), tall morningglory (Ipomoea purpurea), henbit (Lamium ~E~ 3~ jlmsonweed (Datura stramonium~, black 20 nightshade (Solanum niqrum), persian speedwell (Veronica persica~, common cocklebur (Xanthium pensylvanicum), co~non sunflower (Elelianthus annuus), etc. Examples of Grami-naceous weeds are Japanese millet (Echinochloa frumen-tacea), barnyardgrass (Echinochloa crus-galli), green foxtail 25 (Setaria viridis), large crabgrass tDigitaria san~uinalis), annual bluegrass (Poa annua), blackgrass (Alopecurus myosuroides), oats ~Avena sativa), wild oa-ts (Avena fatua), johnsongrass (Sor~hum hale~ense), etc. Examples of 30Commelinaceous weeds are asiatic dayflower (Commelina communis), etc. Examples of Cyperaceous weeds are yellow nutsedge (~yE~rus esculentus), etc.
Further, the tetrahydrophthalimides are effective in exterminating paddy Eield weeds including Graminaceous weeds such as barnyardgrass (Echinochloa oryzicola), broad-leaved weed such as common falsepimpernel (Lindernia procumbens), indian toothcup (Rotala indica) and waterwort (Elatine triandra), Cype-raceous weeds such as hardstem bulrush ~Scirpus juncoides) and needle spikerush (Eleocharis acicularis~ and others such as monochoria (Monochoria vaqinalis) and arrowhead (Sagittaria py~maea)l without any phytotoxicity to rice plants on flooding treatment~
Specific examples of the tetrahydrophthalimides are 2-~1-(2-propenyl)-2(lH)-quinoxalinon-7-yl]-4,5,6,7-tetra-hydro-2H-isoindole-1,3-dione, 2-[3,4-dihydro-1-(2-propynyl)-2(1~)-quinoxalinon-7-yl]-4,5,6,7-tetrahydro-2H-isoindole-1,3-dione, 2-[6-fluoro-1-(2-propenyl)-2~1H)-quinoxalinon-7-yl]-4,5,6,7-tetrahydro-2H-isoindole-1,3-dione, 2-[3,4-di-hydro-6-fluoro-1-(2-propynyl)-2(lH)-quinoxalinon-7-yl]-

4,5,6,7-tetrahydro-2H-isoindole-1,3-dione, etc.

On the practical usage of the tetrahydrophthal-imides they may be applied in any preparation form such as emulsifiable concentrates, wettable powders, suspensions, granules, etc. in combination with conventional solid or liquid carriers or diluents as well as surface active agents or auxiliary agents. The content of the tetrahydrophthal-imides as the active ingredient in such formulation form is usually within a range of 0.05 to 90 % by weight, pre-ferably of 0.1 to 80 ~ by weight. Examples of the solid carrier or diluent are fine powders or granules of kaolin clay, attapulgite clay, bentonite, terra alba, pyrophyllite, talc, diatomaceous earth, calcite, walnut powders, urea, ammonium sulfate and synthetic hydrous silicate, etc. As the liquid carrier or diluent, there may be exemplified aromatic hydrocarbons (e.g. xylene, methylnaphthalene), alcohols (e.g. isopropanol, ethylene glycol, cellosolve~, ketones (e.gO acetone, cyclohexanone, isophorone), soybean oil, cotton seed oil, dimethyls~lfoxide, N,N-dimethylform-amide, acetonitrile, water, etc.
The surface active agent used for emulsification, dispersion ox spreading may be any of the anionic and lS non-ionic type of agents. Examples of the surface active agent include alkylsulfates, alkylarylsulfonates, dialkyl sulfosuccinates, phosphates of polyoxyethylenealkylaryl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers~ polyoxyethylene polyoxypropylene block copolymer, sorbitan fatty acid esters, polyoxyethylene sorbitan ~atty acid esters, etc. Examples of the auxiliary agents include ligninsulfonates, sodium alginate, polyvinyl alcohol, gum arabic, CMC tcarboxymethyl cellulose), PAP
(isopropyl acid phosphate), etc.

Practical embodiments of the herbicidal composition according -to tlle invention described in Canadian Patent Application Serial No. 492,126 filed October 3, 1985 from which the present invention has been divided are illustratively shown

5 in the following examples wherein parts are by weight. The compound number of the active ingredient corresponds to the one in Table 3.

Formulation Example 1 Fifty parts of Compound No. 14, 3 parts of calcium ld ligninsulfonate, 2 parts of sodium laurylsulfate and 45 parts of synthetic hydrous silicate were thoroughly mixed while being powdered to form a wettable ~owder.
Formulation Example 2 Fi~e parts of Compound No. 8, 14 parts of poly-15 oxyethylenestyryl.phenyl ether, 6 parts of calcium dodecyl-benzenesu].fonate, 30 parts of xylene and 45 parts of N,N-dimethylformamide were thoroughly mixed to form an emulsi-fiable concentrate.
Formulation Example 3 Two parts of Compound No. 5, 1 part of synthetic hydrous silicate, 2 parts of calcium ligninsulfonate, 30 parts of bentonite and 65 parts of kaolin clay were thor-oughly ~.ixed while being powdered. The mixture was then kneaded with water, granulated and dried to form granules.

Formulation Example 4 Twenty-five parts of Compound No. 8 were mi~ed with 3 parts of polyoxyethylene sorbitan monooleate, 3 parts of carboxymethyl cellulose and 69 parts of water and pulverized until the particle size of the mixture became less than 5 microns to form a suspension.
The tetrahydrophthalimides thus formulated in any suitable formulation are useful for the pre-emergence or post-emergence control of undesired weeds by soil or foliar treatment as well as flood fallowing treatment. These treatments include the application to the soil surface prior to or after transplanting or incorporation into the soil. The foliar treatment may be efected by spraying the herbicidal composition containing the tetrahydrophthalimides over the top of the plants.
It may also be applied directly to the weeds if care is taken to keep the chemical off the crop foliage.
The tetrahydrophthalimides may be used together with other herbicides to improve their activity as herbicides, and in some cases, a synergistic effect can be expected.
Further, they may be applied in combina-tion with insecticides, acaricides, nema-tocides, fungicides, plant growth regulators, fertilizers, soil improvers, etc.
Furthermore, the tetrahydrophthalimides can be used as herbicides applicable to agricultural plowed field as well as paddy field. They are also useful as herbicides to be employed for orchaxds, pasture land, lawns, forests, non-3~

agricultural fields, etc.
The dosage rate of the tetrahydrophthalimides may vary depending on the prevailing weather conditions, the formulation used, the prevailing season, the mode of appli-cation, the soil involved, the crop and weed species, etc.
Generally, however, the dosage rate is from 0.02 to 100 grams, preferably from 0.05 to 50 grams, of the active in-gredient per are. The herbicidal composition formulated in the form of an emulsifiable concentrate, a wettable powder or a suspension may ordinarily be employed by diluting it with water at a volume of 1 to 10 liters per are, if necessary, with the addition of an auxiliary agen~
such as a spreading agent. Examples of the spreading agent include, in addition to the surface active agents as noted above, polyoxyethylene resin acid (ester), ligninsulfon-ate 7 abietylenic acid salt, dinaphthylmethane-disulfonate, paraffin, etc. The composition formulated in the form of granules may normally be applied as such without dilution.
The biological data of the tetrahydrophthalimides as herbicides is illustratively shown in the following Examples wherein the phytotoxicity to crop plants and the herbicidal activity on weeds were observed visually as to the degree of germination as well as the growth inhibition and rated with an index 0, 1, 2, 3, 4 or 5, in which the nu-meral "0" indicates that no material difference is seen in comparison with the untreated plant and the numeral "5" which indicates complete inhibition or death of the test plants.

The compounds shown in Table 4 below were used for comparison.
Table 4 CompoundChemical structure ¦ Remarks A /Cl Commercially r-~ r-~ available herbi-C1~/ \ ~ ~/ ~NO2 cide; "chloro-~ ~ Cl nitrofen"

Test Example 1 Cylindrical plastic pots (diameter, 10 cm; hei.ght, 10 cm) were filled with upland field soil, and the seeds of Japanese millet, tall morningglory and velvetleaf were sowed therein and covered with soil. A designated amount of the test compound formulated into an emulsifiable concentrate according to Formulation ~xample 2 was diluted with water, and the dilution was sprayed onto the soil surface by means of a small hand sprayer at a spray volume of 10 liters per are. The test plants were further grown in a greenhouse for 20 days, and the herbicidal activity was examined.
The results are shown in Table 5.

Table 5 Compound ¦ Dosage Herbicidal activity No. tg/are) Japanese Tall morning- Velvet-millet glory leaf 10 ~ ~

_ _ A L 12 1 I 0 _ Test Example 2 Cylindrical plastic pots (diameter, 10 cm; height, 10 cm) were filled with upland field soil, and the seeds of Japanese millet, radish and velvetleaf were sowed therein and cultivated in a greenhouse for lO days. A designated amount of the test compound formulatedinto an emulsifiable concentrate according to Formulation Example 2 was diluted with water containing a spreading agent, and the dilution was sprayed over the foliage of the test plants by means of a small hand sprayer at a spray volume of lO liters per are.
The test plants were further grown in the greenhouse for 20 days, and the herbicidal activity was examined.
The results are shown in Table 6.

19 ~ 3 Table 6 Compound Dosage Herbicidal activity No. (g/are) millet Radish ¦ Velvetleaf ¦

1 . T

Test Example 3 Cylindrical plastic pots (diameter, 8 cm; height, 12 cm) were filled with paddy field soil, and the seeds of barnyardgrass (Echinochloa oryzicola) and broad-leaved weeds -(e.g. common falsepimpernel, indian toothcup, waterwort) were sowed in 1 to 2 cm depth. Water was poured therein to make a flooded condition, and rice seedlings at the 2-leaf stage were transplanted therein and grown in a greenhouse.
Six days (at that time the weeds began to germinate) there-after, a designated amount of the test compound formulated in an emulsifiable concentrate according to Formulation Example 2 and diluted with water (5 ml) was applied to the pots by perfusion. The test plants were grown for further 20 days in the greenhouse, and the herbicidal activity was examined.
The results are shown in Table 7.
Table 7 Compound Dosage Herbicidal activity No. (g/are) Rice plant Barnyard- Broad-leaved grass weed 14 20 0 ~ 4 ~ 55 = ~0 ~ ~ 0 1 5 Test Example 4 Vats ~33 cm x 23 cm x 11 cm) were filled with upland field soil, and the seeds of soybean, cotton, corn, co~mon cocklebur, tall morningglory, velvetleaf, redroot pigweed, black nightshade, barnyardgrass and green foxtail were sowed therein to 1 to 2 cm depth. A designated amount of the test compound formulated in an emulsifiable concentrate according to Formulation Example 2 was diluted with water, and the dilution was sprayed onto the soil surface by means of a small hand sprayer at a spray volume of 10 liters per are. The test plants were further grown in a greenhouse for 20 days, and the herbicidal activity was examined.
The results are shown in Table 8.

-- a I, ~ ~ ~ ~ ~ ~ o _ ~ o~ ~o ~ _ __ D :~
0 3 u~ ) _ :~ l ~1 ~ ~ n _ t-d D ~ O .-1 ~ ~ ~ u~ I u~ I O
~ E~ 6 2~
C

6 . :1 I ~ Ul I ~ I O
_ _ .
O 0~11110 O

a ~o o_ I I I I o o , ~
00 cl ~
,n ~0~ u~ u~
E~ _ :~ c~ O ~ ~ ~
6z ~ _ - 22 - ~ ~5 Test Example 5 Vats (33 cm x 23 cm x 11 cm~ were filled with upland field soil, and the seeds of wheat, catchweed bedstraw, persian speedwell, common chickweed, common lambsquarters, pale smartweed, wild buckwheat and annual bluegrass were sowed therein to 1 to 2 cm depth. A designated amount of the test compound formulated into an emulsifiable concentrate according to Formulation Example 2 was diluted with water, and the dilution was sprayed onto the soil surface by means of a small hand sprayer at a spray volume of 10 liters per are. The test plants were further grown in 2 greenhouse for 27 days, and the herbicidal activity was examined.
The results are shown in Table 9.

__ ~ ~ o 3-~S ~ o ~ o 'r~ ~3~o O b~ ~ u~ n O

_ o o 3 u~ o .
~ u~ O
~ 3 . ~: ~ _ C~ D I 11~ 1 ~ O
3 __oo o _ o~ oo~ U)~ U~
D ~ ~ -- C~ C~l t"l _ _ ~ 111~0~ ~

Test Example 6 ._ _ Vats (33 cm x 23 cm x 11 cm) were filled with upland field soil, and the seeds of corn, wheat, sugar beet, common coc~lebur, velvetleaf, black niyhtshade, tall morning-glory, common lambsquarters and green foxtail were sowedtherein and cultivated for 18 days in a greenhouse. A
designated amount of the test compound formulated in an emulsifiable concentrate according ko Formulation Example 2 was diluted with water containing a spreading agent, and the dilùtion was sprayed over the foliage of the test plants by means of a small hand sprayer at a spray volume of 5 liters per are. The test plants were further grown in the green-house for 20 days, and the herbicidal activity was examined.
At the time of application, the tesk plants were qenerally at the 1 to 4 leaf staqe and 2 to 12 cm in height, although the growth stage of the test plants varied depending on their species.
The results are shown in Table 10.

3~

C~ I I I I I ~ oo ~,~
o ~ ~ u~ n _ O

a E~ ~ 0 0 ~ ~ V ~ ~ U~ o o ~ ~I T~ r V O _ ~ ~ ~a u~ _ O
h _ .

U D U-) ~J 117 U~ r) U~ U-) O O
~ ~J
00 I ~ O O

_~ 10_ C~O :
_ ~110_-1_01 00 .
_ . .
O . ~ ~ ~ ~ r~ ~ r~ ~

P o o o o o o o o o o o o ~ ~ ¢

Claims (10)

Claims:

1. A compound of the formula:
wherein X is a hydrogen atom, a fluorine atom or a chlorine atom and A is or in which R2 is a hydrogen atom or a methyl group, R3 is a hydrogen atom or a methyl group and the nitrogen atom is bonded to the benzene ring.

2. A compound as claimed in claim 1 wherein X is a fluorine atom.

3. A process for preparing a compound of the formula:

wherein X is a hydrogen atom, a fluorine atom or a chlorine atom and A is or in which R2 is a hydrogen atom or a methyl group, R3 is a hydrogen atom or a methyl group and the nitrogen atom is bonded to the benzene ring which process comprises, to obtain a compound in which A is , subjecting a compound of the formula:

in which X, R2, R3 and R4 are as defined above to reduc-tive cyclization with a reducing agent, and, if required, to obtain a compound in which A is , oxidizing the compound obtained by the reductive cyclization reaction.

4. A process as claimed in claim 3 wherein the reducing agent is iron in an acid.

5 . A process as claimed in claim 3 wherein the reductive cyclization is conducted by treating the N-phenyl-amino acid ester with 3 to 10 equivalent amounts of powdery iron in a solvent in the presence of an excess of an acid.

6. A process as claimed in claim 5 wherein the solvent is water, alcohol, acetic acid or ethyl acetate.

7. A process as claimed in claim 5 wherein the acid is acetic acid or hydrochloric acid.

8. A process as claimed in claim 5 , 6 or 7 wherein the reaction is conducted at a temperature of 50 to 200°C.

9. A process as claimed in claim 3 wherein the oxidation is conducted in an excess of hydrogen peroxide in the presence of sodium hydroxide.

10, A process as claimed in claim 3 wherein the compound of the formula:
in which X, R2, R3 and R4 are as defined in claim 3, is obtained by reacting an N-nitrophenylphthalimide of the formula:
in which X is as defined in claim 3 , with an amino acid ester of the formula:
in which R2, R3 and R4 are as defined in claim 3