Synthesis of thiazolotriazepinones

Abstract
The synthesis of 4,5‐dihydro‐7‐phenylthiazolo[2,3‐c][1,2,4]triazepin‐3(2H)‐one (4) from 2‐propenoic acid 2‐(4‐phenyl‐2‐thiazolyl)hydrazide (14), is reported. A synthesis of 4 which was reported earlier by Mahajan, Sondhi and Ralhan (9), from 3‐chloropropanoic acid 2‐(4‐phenyl‐2‐thiazolyl)hydrazide (3), is erroneous. We were able to cyclize 3 to 1‐(4‐phenyl‐2‐thiazolyl)‐3‐pyrazolidinone (5). The cyclizations of 14 to 4 and 3 to 5 are consistent with the Baldwin Rules for Ring Closure.