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 novel 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.
