Synthesis of 1,2,5‐Thiadiazepine Derivatives by Ring Enlargement of 1,2‐Thiazetidin‐3‐one 1,1‐Dioxides with 3‐Amino‐2 H ‐azirines

At 0° in MeCN, 2,2‐disubstituted 3‐amino‐2 H ‐azirines 1 and 4,4‐disubstituted 1,2‐thiazetidin‐3‐one 1,1‐dioxides 7 react smoothly to give 1,2,5‐thiadiazepin‐6‐one 1,1‐dioxides of type 8 ( Scheme 2 ). The reaction mechanism of this regiospecific ring enlargement to seven‐membered heterocycles follows previously described pathways. The structures of 7a and 8b were established by X‐ray crystallography (see Figs. 1 and 2 ).