Chemoselective reactions under solvent-free conditions: lanthanide-catalyzed syntheses of 2-amino-3,1-benzothiazines and 3,4-dihydroquinazoline-2-thiones

Abstract

A catalyst-controlled chemoselective reaction of o-aminocinnamate and isothiocyanates in the presence of lanthanide complexes under mild and solvent-free conditions was developed. 2-Amino-3,1-benzothiazines were obtained in high yields when the reactions were catalyzed by Yb(OTf)₃, whereas those catalyzed by [(Me₃Si)₂N]₃La(μ-Cl)Li(THF)₃ afforded 3,4-dihydroquinazoline-2-thiones in high to excellent yields. The mechanism for the product selectivity and high efficiency of the reaction was proposed.