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A Cu(I)-catalysed synthesis of substituted 3-methyleneisoindolin-1-ones using alkynyl acids as an alkyne source has been developed. The reaction involves the decarboxylative cross-coupling of 2-halobenzamides with aryl alkynyl acids, followed by 5-exo-dig heteroannulation. While reactions of 2-iodo benzamides proceeded without a ligand, for 2-bromo substrates, the assistance of a ligand is essential.

Different reactivities and selectivities of Cu and Pd catalysts have been demonstrated in the reactions of benzylamines with 2-phenylpyridines. Although Pd is reported to give o-arylation (ArCO–), Cu introduces an arylcarboxy group (ArCOO–) at the proximal site of the directing group. For the first time benzylamine has been utilised as a synthetic equivalent of an arylcarboxy group.

An efficient metal free oxidative esterification of sp(3) C-H bonds (adjacent to an oxygen atom) in simple solvents like 1,4-dioxane, tetrahydropyran, tetrahydrofuran and ethyl acetate has been achieved using terminal aryl alkenes and alkynes as the ArCOO(-) sources.

A metal free synthesis of 3-aroylindole involving two sp3C–H activation has been achieved starting fromo-alkynyl-N,N-dialkylamines using TBAI–TBHP.

In the present study, three divergent reaction paths emerged when o-haloanilides were subjected to CuO nanoparticles in water. o-Halo (I, Br) phenylbenzamides in the presence of CuO nanoparticles and Cs2CO3 in water at 100 °C provided o-hydroxyphenyl benzamides as the major product. However, a complete change in selectivity was observed in the presence of an organic base/ligand (TMEDA), giving 2-arylbenzoxazole as the exclusive product. The above selectivities were not clearly distinct when the corresponding alkylamides were treated either in the presence or absence of the ligand. A number of o-halophenyl alkylamides provided either exclusively o-dehalogenated products or a mixture of o-dehalogenated and o-hydroxylated products, but none gave 2-alkylbenzoxazoles. In addition to the above selectivities, the use of an environmentally friendly solvent (water) and base, and the recyclability of the catalyst make this procedure a benign alternative to the existing methods for the synthesis of these molecules, viz. o-hydroxybenzamides and o-arylbenzoxazoles.

An “on-water” one-pot process has been engineered for the preparation of 2-aminobenzothiazole from ortho-halo (–F, –Cl, –Br and –I) substituted unsymmetrical thioureas. For ortho –I and –Br substrates the reactions afford 2-aminobenzothiazoles under metal free condition promoted by base. However, the relatively inert ortho –Cl and –F substrates undergo intramolecular arylthiolation only in the presence of CuO nanoparticles yielding 2-aminobenzothiazoles. This methodology provides easy access to aminobenzothiazoles utilising even the ortho –Cl and –F substrates. The catalyst is recyclable several times without loss of substantial activity. Other remarkable features include the wide range of functional group tolerance, absence of chromatographic purification (for ortho –I and –Br substrates) and providing moderate to excellent yield of the products under mild conditions, thus rendering the methodology as a highly eco-friendly alternative to the existing methods.

A one-pot synthesis of 3-amino-1,3,4-oxadiazoles has been achieved from the corresponding dithiocarbamate salt, employing the thiophilic property of molecular iodine. The precursor thiosemicarbazides could be derived in situ which underwent an intramolecular cyclodesulfurization in the presence of iodine to afford 3-amino-1,3,4-oxadiazoles exclusively. Apart from being milder and environmentally sustainable, this method involves a simple, reliable approach to give good to excellent yields of the desired products and is compatible with a wide range of functional groups.

A one-pot, tandem process has been developed for the synthesis of a library of tetrazoles from aryl isothiocyanates. Condensation of aryl isothiocyanates with ammonia, and aryl amines (R-NH(2)) provided mono, 1,3-disubstituted symmetrical and unsymmetrical thioureas, which on desulfurization with molecular iodine (I(2)) led to formation of the corresponding heterocumulene (cyanamides or carbodiimides). The in situ generated heterocumulene on subsequent treatment with sodium azide at room temperature gave corresponding tetrazoles. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas was found to be correlated with the basicities (pK(a)'s) of the parent amines attached to the thiourea. Aryl-sec-alkyl unsymmetrical thioureas gave thioamido guanidino products rather than the 5-aminotetrazoles produced by HgCl(2) mediation of the reaction. Bis-thioureas derived from aryl isothiocyanates and hydrazine gave thiadiazoles exclusively.