Synthesis of 2-(2-Dialkylamino-4H-3,1-benzothiazin-4-yl)acetic Acid Derivatives and 2-(2-Thioxo-1,2,3,4-tetrahydroquinazolin-4-yl)acetic Acid Derivatives

Abstract

An efficient method for the preparation of 2-(4H-3,1-benzothiazin-4-yl)acetic acid derivatives and 2-(2-thioxo-1,2,3,4-tetrahydroquinazolin-4-yl)acetic acid derivatives has been developed. The reaction of 3-(2-isothiocyanatophenyl)propenoic acid derivatives with secondary amines in methanol at room temperature gave the corresponding thiourea intermediates, which on heating at reflux temperature cyclized by an attack of the sulfur atom on the propenoic moiety in a 1,4-addition manner, to give 2-(2-dialkylamino-4H-3,1-benzothiazin-4-yl)acetic acid derivatives in one pot. A similar sequence using primary amines in place of secondary amines afforded 2-[3-alkyl(or aryl)-2-thioxo-1,2,3,4-tetrahydroquinazolin-4-yl]acetic acid derivatives.