Harisadhan Ghosh

Intra- and Intermolecular C−S Bond Formation Using a Single Catalytic System: First Direct Access to Arylthiobenzothiazoles

We have for the first time developed two ligand-assisted Cu(I)-catalyzed sequential intra- and intermolecular S-arylations leading to the direct synthesis of arylthiobenzothiazoles in one pot without an inert atmosphere. Low catalyst loading, inexpensive metal catalyst and ligand, lower reaction temperature, and shorter reaction times make this method superior to all reported methods for the synthesis of arylthiobenzothiazole.

Hypervalent Iodine(III)-Mediated Regioselective N-Acylation of 1,3-Disubstituted Thioureas

Reaction of asymmetrical 1,3-disubstituted thioureas with diacetoxyiodobenzene (DIB) produces regioselectively N-acetylurea in shorter time. Regioselectivity is dependent on the pKas of the amine attached to the thiourea moiety with acylation taking place toward the amine having a lower pKa. This is the first example of DIB being employed as an N-acetylating agent. A mechanism for this novel transformation is also proposed. Mild reaction conditions, shorter reaction times, high efficiencies, environmentally benign methods, and facile isolation of the desired product make the present methodology a most suitable alternative.

It is “2-imino-4-thiazolidinones” and not thiohydantoins as the reaction product of 1,3-disubstituted thioureas and chloroacetylchloride

The products obtained by the reaction of 1,3-disubstituted thioureas with chloroacetylchloride are actually 2-imino-4-thiazolidinone derivatives and not thiohydantoins as previously reported (M. Kidwai, R. Venkataraman and B. Dave, Green. Chem., 2001, 3, 278). A highly efficient method for the preparation of 2-imino-4-thiazolidinones has been achieved from both symmetrical and unsymmetrical thioureas in the absence of base. The reaction gives a regioselective product for unsymmetrical thiourea which is dependent on the pKas of the amines. For unsymmetrical thiourea, regioselective 2-imino-4-thiazolidinone formation takes place with the amine attached to the thiourea having lower pKa as part of the imino component and the amine having higher pKa contributes to the other heterocyclic nitrogen.

Efficient Preparation of Isothiocyanates From Dithiocarbamates Using Bromineless Brominating Reagent

For the first time, the crystal structure of a ditribromide reagent 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT) has been determined. Utilizing this thiophilic bromineless brominating agent EDPBT, highly useful synthetic intermediates (alkyl and aryl isothiocyanates) have been achieved directly from dithiocarbamates. EDPBT can be easily prepared from readily available reagents. It has been used as a thiophilic reagent, and its thiophilicity dominates over its brominating ability for substrates amenable to bromination. This is a sustainable process for the preparation of isothiocyantes because the spent reagent can be recovered, regenerated, and reused.

Oxidative desulfurization of disubstituted thioureas using Pb(II) salts and investigation of pKa-dependent regioselective N-acylation

A highly efficient method for the N-acylation of both symmetrical and unsymmetrical thioureas by the use of lead (II) salts and triethylamine has been achieved. The reaction gives regioselective N-acylated product for unsymmetrical thiourea. For unsymmetrical thiuourea, regioselective N-acylation takes place towards the amine having lower pK a. A linear correlation between the pK as of the amines and the regioselective N-acylation is found. Another attractive feature of this transformation is that lead sulfide, which is important to material science, is obtained as a side product (nanocubes of 20 nm).