Selective synthesis of 2-aminobenzoxazoles and 2-mercaptobenzoxazoles by using o-aminophenols as starting material

Synthesis of Various 2-Aminobenzoxazoles: The Study of Cyclization and Smiles Rearrangement

This study reports two synthetic approaches leading to 2-aminobenzoxazoles and their N-substituted analogues. Our first synthetic strategy involves a reaction between various o-aminophenols and N-cyano-N-phenyl-p-toluenesulfonamide as a nonhazardous electrophilic cyanating agent in the presence of Lewis acid. The second synthetic approach uses the Smiles rearrangement upon activation of benzoxazole-2-thiol with chloroacetyl chloride. Both developed synthetic protocols are widely applicable, afford the desired aminobenzoxazoles in good to excellent yields, and use nontoxic and inexpensive starting material.

Metal-Free Synthesis of 2- N, N-Dialkylaminobenzoxazoles Using Tertiary Amines as the Nitrogen Source

The unprecedented reaction of tertiary amines with 2(3 H)-benzoxazolones has been investigated. In the presence of the Ph₃P-I₂ reagent system, the reaction of both acyclic and cyclic aliphatic tertiary amines led to the formation of 2- N, N-dialkylaminobenzoxazoles with the selective cleavage of an alkyl group. Especially, N-(2-iodoethyl)piperazinyl derivatives were rapidly produced in good yields when using DABCO as the nitrogen source. Only in the cases when the nucleophilicity of the substrates exceeds that of the amine, competitive self-condensation of benzoxazolones then proceeds preferentially. ³¹P{¹H}-NMR study suggested the involvement of an aryloxyphosphonium intermediate and/or possibly 2-iodobenzoxazole which activates the C-2 position of benzoxazolones toward nucleophilic aromatic substitution.

One-Pot Synthesis of 2-Benzyl/2-Allyl-Substituted Thiobenzoazoles Using Transition-Metal-Free Conditions in Water

A transition-metal-free protocol for the one-pot synthesis of 2-benzyl/2-allyl-substituted thiobenzoazoles in water was developed. The cyclization of 2-aminothiophenols, 2-aminophenols, and 1,2-phenylenediamines with tetramethylthiuram disulfide (TMTD) gave mercapto benzoheterocycles, and the subsequent C-S coupling with benzyl or allyl halides furnished the desired products in good to excellent yields. This method features transition-metal-free conditions with water as a solvent, an easy performance, mild reaction conditions, a wide substrate scope, and good to excellent yields, thus paving an efficient and useful way to establish a library of potentially active drug molecules.

Copper(I)-Catalyzed Tandem One-Pot Synthesis of 2-Arylthiobenzothiazoles and 2-Arylthiobenzoxazoles in Water

An efficient tandem process for the preparation of 2-arylthiobenzothiazoles has been developed. By condensation of 2-aminobenzenethiol with tetramethylthiuram disulfide (TMTD), 2-mercaptobenzothiazoles was in situ generated, which susequently underwent coupling with iodobenzenes to give the desired 2-arylthiobenzothiazoles fluently in a one-pot manner. This method can also be used for the synthesis of 2-arylthiobenzoxazoles. Inexpensive metal catalyst and ligand, mild reaction temperature, and water as solvent make this protocol practically valuable and useful in organic synthesis.