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A regiospecific C−H/S−H annulation of quinoline-4(1H)-thiones with alkynes have been demonstrated using a ruthenium(II) catalyst. This C−H/S−H annulation is directed via the C=S group, where preferential annulation takes place at the sterically hindered position even in the presence of three other competing sites viz. two C−H/N−H and one C−H/O−H. This type of annulation is unsuccessful for simple aryl thiol such as 1-naphthylthiol, giving only an oxidative dimerized product. The reaction proceeds via ruthenium-catalyzed oxidative annulation followed by a hydrolytic cleavage of an amidic bond (loss of −COPh group), leading to the synthesis of thiopyrano[2,3,4-de]quinolines. Isotopic labelling experiments suggest an irreversible initial C−Ru bond formation and the cleavage of C−H bond to be the rate-limiting step. The reaction with unsymmetrical and terminal alkynes gave single regioisomeric product, where the new C−S bond formation takes place at the sp-carbon of alkyne having more electron density. The reaction shows wide substrate scope both for quinoline-4(1H)-thiones as well as alkynes giving up to 91% product yields.

A palladium‐catalyzed isocyanides insertion into 2‐halophenoxy acrylates leading to an unparalleled synthesis of dihydrobenzofurans (DHBs) having two exocyclic double bonds have been achieved. While the iodo substrates gave products having an exocyclic imine bond, its bromo analogue yielded reduced secondary amines as the product. An acid hydrolysis of the exocyclic imine bond in DHBs produces various aurone esters.

An iron(III)-catalyzed C-3 functionalization of flavones has been achieved using tert-butyl peroxybenzoate (TBPB)/potassium persulphate (K2S2O8) oxidant combinations with a suitable solvent. In the presence of iron(III)/tert-butyl peroxybenzoate/potassium persulphate, the reaction of flavones in cycloalkanes afforded exclusive C-3 cycloalkylation via Csp2 –Csp3 coupling, whereas the solvent N,N-dialkylformamide provided C-3 amidation via Csp2 –Csp2 coupling. Under identical reaction conditions just by switching the solvent to chlorobenzene, C-3 methylated flavones were obtained where tert-butyl peroxybenzoate (TBPB) served as the source of the methyl group.

A copper(II)-catalyzed oxidative methylene-bridged dimerization of two analogous imidazo[1,2-a]pyridines has been achieved using N,N-dimethylacetamide (DMA) as solvent cum methylene source. This reaction works with a variety of substituted imidazo[1,2-a]pyridines giving their products in moderate to good yields. Isotopic labelling experiments revealed that the methylene group in the product originates from the N,N-dimethyl moiety of DMA.

An unprecedented palladium(II)-catalyzed biomimetic aliphatic acyl (-COR) group transfer was observed from acyl-α-peroxycoumarins to the ortho CH sites of directing arenes. Here, the CH activation is associated with a concomitant acyl group transfer via a Pd(II)-catalyzed, redox-neutral process. While methods for ortho aroylation (-COAr) are well documented ortho acylation (-COR) processes are scarce, hence the present redox-neutral method is most ideal for o-acylation of directing substrates.

An efficient copper‐catalyzed protocol has been developed for the synthesis of carbamates from dialkylformamides and phenols possessing directing groups such as benzothiazole, quinoline and formyl at the ortho‐position. In this chelation assisted approach, C-O bond formation takes place via a Cross Dehydrogenative Coupling (CDC) between the formyl C-H of dialkylformamide and phenolic O-H in the presence of copper(II)acetate/aqueous tert‐butyl hydroperoxide. Under identical reaction conditions, salicylic acid derivatives underwent amidation with the carboxylic group rather than formamidation of the phenolic OH. The use of a cheap and environmentally benign catalyst along with the tolerance of a wide range of functional groups makes this an easy, phosgene‐free route to carbamates.

A unique copper-catalyzed cross-dehydro- genative coupling (CDC) of thiols and alkylbenzenes has been developed for the synthesis of thioesters without the assistance of any directing group. A thio- ester moiety is created via successive CS and CO bond formation at the expense of three sp 3 CH bonds of the alkylbenzene and one sp 3 SH bond of the thiol.

An acyl moiety generated from a-oxocar- boxylic acids via decarboxylation undergoes a palladi- um-catalyzed chemoselective insertion into organic cyanamides to afford N-monosubstituted a-keto- A

A tandem and convergent approach to var- ious N-, O-, or S-containing azoles has been devel- oped by exploiting the thiophilic property of cop- per(I) iodide used in a catalytic quantity. The present protocol gives access to amino-substituted tetrazoles, triazoles, oxadiazoles and thiadiazoles via oxidative desulfurization of their respective precursors fol- lowed by inter- or intramolecular attack of suitable nucleophiles. For aminotetrazoles and triazoles an excellent regioselectivity has been achieved through proper tuning of the pKa values of the parent amines attached to unsymmetrical thioureas. The method represents an autocatalytic process in which cop- per(I) iodide gets converted to copper(II) sulfide which in turn transforms to active copper(II) oxide that effectively carries forward the catalytic cycle. The fate of the copper catalyst has also been studied using scanning electron microscopic (SEM) and energy-dispersive X-ray spectroscopic (EDS) analy- ses which give an insight into the mechanism for this catalytic process.

We have developed a ligand-assisted copper(I)-catalyzed two sequential heteroarylation sequence. An intramolecular S-arylation is followed by an intermolecular N-arylation leading to the direct synthesis of N-aryl-2-aminobenzothiazoles. In most cases however, the 2-arylsulfanyl-arylcyanamide was the major product obtained via an intramolecular C―S bond formation, associated with C―S bond breakage, followed by an intermolecular S-arylation. The selectivity of this ligand-assisted reaction is quite different as compared to that of ligand-free reactions and the rates are much faster giving good yields of products. Various cyanamides can be prepared in excellent yields from their corresponding 1-substituted thioureas with or without the assistance of a ligand with a catalytic quantity of copper(I).