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.

CuO nanoparticle catalyzed synthesis of 2,3-disubstituted quinazolinones has been accomplished from 2-halobenzamides and (aryl)methanamines under an air atmosphere. This synthesis of the N-heterocycle involves a sequential Ullmann coupling [between 2halobenzamide and (aryl)methanamine], oxidation of the in situ generated secondary amine to imine. This is then followed by an intramolecular nucleophilic attack of the amidic N−H on to the imine carbon (C−N bond formation) resulting in the synthesis of 2,3disubstituted quinazolinones. The recyclability of the catalyst and tolerance of a wide range of functional groups makes this method efficient and cost-effective.

C-3 alkylation of coumarins has been accomplished using cycloalkanes or alkylbenzenes in the presence of di-tert-butylperoxide (DTBP) and Fe(III) catalyst. Under metal free conditions and just by switching the oxidant from DTBP to TBHP, an exclusive C-4 cycloalkylation-C-3 peroxidation reaction takes place. During C-3 alkylation, the C-C bond formation occurs at the expense of an existing C-C bond, while the C-4 alkylation is associated with the formation of new C-C and C-O bonds.

No abstract

Substrate-directed ortho C-H amination of azoarenes using TMSN3 as the source of nitrogen leading to the synthesis of 2-aryl-2H-benzotriazoles has been accomplished with the help of Pd/TBHP combinations. An intermolecular o-azidation (C-N bond formation) followed by an intramolecular N-N bond formation via nucleophilic attack of one of the azo nitrogen onto the o-azide nitrogen leads to cyclization with the expulsion of N2.

By using alkylbenzenes as aroyl surrogates, copper(II) catalyzed chemoselective O-aroylations of 1,3-dicarbonyl compounds and phenolic -OH ortho to carbonyl (-CHO, -COR) groups have been achieved. A dual mechanism operating in tandem for these transformations has been supported by a crossover experiment.

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 Cs 2 CO 3 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 2arylbenzoxazole 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 ohalophenyl alkylamides provided either exclusively o-dehalogenated products or a mixture of odehalogenated 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 elegant synthesis of carboxylic acid anhydrides has been developed directly from arylaldehydes using CuO nanoparticles as the catalyst and tert‐butyl hydroperoxide (TBHP) as the oxidant. During anhydride formation the reaction proceeds through a double sp2 C–H functionalization of aldehydes to generate two consecutive C–O bonds.