A new stereospecific synthesis of 5,6-dihydro-4H1,3-thiazines by polar 1,4-cycloaddition of thioamidoalkyl ions to olefins. Configurational and conformational nuclear magnetic resonance analysis of the products

Abstract

5,6-Dihydro-4H-1,3-thiazines with a wide variety of substituents have been obtained by a one-step condensation of a thioamide, an aldehyde, and an olefin. The reaction proceeds through polar 1,4-cycloaddition of the thioamidoalkyl ion (generated in situ from the aldehyde and the thioamide) to the olefin and is stereospecific and regiospecific. Conformational and configurational n.m.r. analysis has been carried out on the diastereoisomeric pairs of 5,6-dihydro-4H-1,3-thiazines so obtained.