Transannular Anti-Michael Addition: Formation of 4H-Pyrazolo51-cthiazines

摘要

The reaction of 2-(diphenylmethylene)thietan-3-one (>2) with 1,2,4,5-tetrazines (>3a–c) in KOH/MeOH/THF gives 4H-pyrazolo[5,1-c]thiazines (>7a–c). This no vel condensation reaction proceeds via the intermediacy of an 8-(diphenylmethylene)-2H-1,4,5-thiadiazocin-7(8H)-one (>5), which undergoes a multi-step rearrangement including a rare anti-Michael addition.