Evidence for the existence of a new 8 π-electron system, 1,3,5-thiadiazinide anion

Abstract

2,4,6-Triaryl-4H-1,3,5-thiadiazines react with catalytic amounts of aliphatic amines to afford 2,4,5-triarylimidazoles and sulphur in nearly quantitative yield. The proposed intermediate of this reaction is the very reactive, planar, conjugated 8 π-electron system, 2,4,6-triaryl-1,3,5-thiadiazinide anion. Kinetic evidence for formation of this anion is reported. Moreover a hydrogen isotope effect for ring contraction of 2,4,6-triphenyl-[4-²H]4H-1,3,5-thiadiazine is reported. The reaction has been extended to 2,6-diaryl- and 4-alkyl-2,6-diaryl-4H-1,3,5-thiadiazines.