C-H bond activation

Pyrans constitute an important class of 6-member heterocycles with one oxygen atom. Together with its benzo derivatives, pyrans can formulate a prevalent verity of natural and synthetic products with industrial applications. This is an important core molecule having versatile use with its derivatives in pharmaceuticals, dye industry, catalysis, agrochemicals and many more. Several methods for the preparation of pyran derivatives have been reported earlier. This article reports the development of an efficient method for the construction of a fused pyran ring by intramolecular Heck reaction followed by β-H elimination from O-allylated ether. A tetracyclic pyran ring has also been synthesized by intramolecular Heck reaction followed by C–H bond activation from O-methallylated ether.

The complex [Ru(bpy)2(ttma)]+ (bpy = 2,2’-
bipyridine; ttma = 3-hydroxy-2-methylthiopyran-
4-thionate, 1, has previously been
shown to undergo an unusual C-H activation of
the dithiomaltolato ligand upon outer-sphere
oxidation. The reaction generated alcohol and
aldehyde products 2 and 3 from C-H oxidation
of the pendant methyl group. In this report, we
demonstrate that the same products are formed
upon photolysis of 1 in presence of mild
oxidants such as methyl viologen,
[Ru(NH3)6]3+ and [Co(NH3)5Cl]2+, which do
not oxidize 1 in the dark.
This reactivity is engendered only upon
excitation into an absorption band attributed
to the ttma ligand. Analogous experiments
with the homoleptic Zn(ttma)2, 4, also result
in reduction of electron acceptors upon
excitation of the ttma absorbance band.
Complexes 1 and 4 exhibit short-lived
visible fluorescence and long-lived nearinfrared
phosphorescence bands. Singlet
oxygen is both generated and quenched
during aerobic excitation of 1 or 4, but is not
involved in the C-H activation process.

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction cond...

A simple and highly practical method for the synthesis of 2-N-substituted benzothiazoles has been
developed by using nano copper ferrite as a magnetically separable, recyclable catalyst. The present
tandem process allows to get access to a wide range of 2-N-substituted benzothiazoles in good to
excellent yields by the reaction of benzothiazole with nitrogen nucleophiles in the presence of Cs2CO3 as a base. The nano CuFe2O4 could be recovered and reused with no significant loss of catalytic activity.

Ap aper-based colorimetrics ensor system (PBCSS)w as developedt od etect the amounto fb is(pina-colato)diboron(B 2 Pin 2)a nd applied as ah igh-throughput screening protocol in Ir-catalyzed CÀHb orylation. First, 96 ligandsw ere screened for the borylation of benzene,a nd then 12 of them were selected and tested for five sub-strates.T hese reactionm ixtures were spotted in the PBCSS,s howingablue-violet color.T he value of the gray scale of each reaction was obtained from these colored spots and converted to the extent of conversion of B 2 Pin 2. The extentso fc onversion of B 2 Pin 2 obtained from the PBCSS showed good correlation with those obtained from gas chromatography analysis.I na ddition, the modified conversion using blank data showedg ood correlation with the yield of products.

Rhodium catalysed dehydrogenative C-H/N-H functionalization was developed to construct phthalazino[2,3-a]-/indazolo[1,2-a]cinnolines by reacting N-phenyl phthalazine/indazole with alkynes. The synthesized compounds exhibit prominent fluorescence properties in solid and aggregation states. Their application in cell imaging was investigated using various cancer cell lines.

We describe here an efficient ruthenium-catalyzed C–H bond ortho-arylation of 9-(pyrimidin-2-yl)-9H-carbazole by using boronic acids. This methodology exhibits excellent and high site-selectivity, functional group tolerance and was found to give the desired product in moderate to good yields.

Tetrabutylammonium decatungstate (TBADT) has emerged as an efficient and versatile photocatalyst for hydrogen atom transfer (HAT) processes that enables the cleavage of both activated and unactivated aliphatic C−H bonds. Using a recently developed oscillatory millistructured continuous-flow photoreactor, investigations of a decatungstate-catalyzed C(sp 3)−H alkylation protocol were carried out, and the results are presented here. The performance of the reactor was evaluated in correlation to several chemical and process parameters, including residence time, light intensity, catalyst loading, and substrate/reagent concentration. In comparison with previously reported batch and flow protocols, conditions were found that led to considerably higher productivity, achieving a throughput up to 36.7 mmol/h with a residence time of only 7.5 min.

A copper-catalyzed aerobic oxidation of benzylpyridine N-oxides is reported. The N-oxide moiety acts as a built-in activator for the benzylic methylene oxidation, without requirement of additives. Reaction conditions were identified which suppress undesired benzoylpyridine formation via N-deoxygenation involving intermolecular oxygen transfer. The versatility of the N-oxide group of the benzoylpyridine N-oxide reaction products for post-functionalization of the pyridine ring is demonstrated through efficient C–C, C–N, C–O and C–Cl bond forming procedures, with both nucleophiles and electrophiles. Finally, the applicability of the new synthetic methodology is demonstrated in an alternative route towards the antihistaminic drug Acrivastine via three consecutive N-oxide activated C–H functionalization processes, starting from picoline N-oxide.

The catalytic potential of different metal Lewis acids has been assessed for the one-pot tandem
Friedländer annulation and Knoevenagel condensation involving 2-aminobenzophenone, ethyl
10 acetoacetate, and benzaldehyde to form 2-styryl quinoline under solvent free condition. While various
metal Lewis acids were effective in promoting the Friedländer annulation step, In(OTf)3
was the only
effective catalyst for the subsequent Knoevenagel condensation reaction suggesting In(OTf)3
as the standalone
catalyst for the tandem Friedländer-Knoevenagel reaction to form 2-styryl quinolines. The protocol
is compatible with different variation of aromatic/hetero-aromatic aldehydes and α, β unsaturated
15 aromatic aldehyde giving highly functionalized 2-aryl/heteroaryl vinyl quinolines. The catalyst can be
recovered and reused to afford the desired product in very good to excellent yields.

Platinum(II) complexes have been investigated for C-H bond activation and functionalization reactions. The synthesis and characterization of new platinum complexes are reported. Studies were performed to investigate the reactivity of these complexes with respect to C-H bond activation, functionalization by dioxygen, and catalytic C-C bond formation.

The reaction of the ligands di-tert-butyl(1-napthyl)phosphine and di-tert-butyl(N-indolyl)phosphine with a platinum(II)-methyl starting material leads to the formation of (PC)PtMe(SMe 2) complexes in which the phosphine ligand has been cyclometalated at a sp2 carbon. These complexes have been shown to activated the C-H bonds of benzene to form isolable Pt-Ph complexes upon thermolysis.

Platinum complexes of the anionic PN ligand N-(2-diphenylphosphinophenyl)-2,6-dimethylanilide were synthesized and characterized. Reductive elimination of ethane from unstable Pt(IV) complexes occurs trans to the phophine moiety to yield Pt(II) complexes which can be trapped by added ligands. Reaction of the neutral N-(2-diphenylphosphinophenyl)-2,6-dimethylaniline ligand with Pt(II) materials led to the formation of complexes in which the N-H exhibits intramolecular hydrogen bonding to the metal center. Thermolysis of these complexes leads to C-D bond activation of C6D6.

A Pt(II)Me2 complex of the ligand 2-((di-tert-butylphosphino)amino)pyridine has been synthesized and characterized. Thermolysis of this complex in benzene leads to the loss of methane and formation of a Pt-Ph product via C-H bond activation. It was demonstrated that the N-H group on the ligand is involved in the methane loss based on labeling studies. A platinum species in which the N-H ligand had been deprotonated was trapped via thermolysis of the Pt(II)Me 2 complex in the presence of pyridine.

A Pt(II)Me2 complex of the ligand 2-((di-tert-butylphosphino)methyl)pyridine has been synthesized and characterized. This species reacts with molecular oxygen to form a Pt-OOMe species, formed from the insertion of dioxygen into a Pt-Me bond. The Pt-OOMe species has been structurally characterized. Evidence is presented which supports this reaction proceeding through a radical mechanism. This novel reactivity is compared with similar reactions at platinum and palladium and the implications for C-H bond functionalization reactions are discussed.

Several platinum complexes have been screened for C-H activation of benzene and catalytic hydroarylation of unactivated olefins. Neutral platinum(II) complexes coordinated by a 2-(2'-pyridyl)-pyrrolide ligand or a 2-(6'-methyl-2'-pyridyl)pyrrolide ligand have been synthesized and studied for hydroarylation. A known [(8-hydroxyquinoline)Pt(IV)Me 3]2 complex was observed to be viable precatalyst for hydroarylation. In addition, Pt(II)Cl2 complexes of the ligands 2,2'-dipyridylamine and 2,2'-dipyridyl-N-butylamine were found to be catalysts for hydroarylation when activated by sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate.