Reaction of sulfene with heterocyclic N,N ‐disubstituted α‐aminomethyleneketones. X. Synthesis of thieno[2,3‐ h ]‐1,2‐benzoxathiin derivatives

The polar 1,4‐cycloaddition of sulfene to N,N ‐disubstituted ( E )5‐aminomethylene‐6,7‐dihydrobenzo[ b ]‐thiophen‐4(5 H )ones II gave in excellent yield and only in the case of aliphatic N ‐substitution, N,N ‐disubstituted 4‐amino‐3,4,5,6‐tetrahydrothieno[2,3‐ h ]‐1,2‐benzoxathiin 2,2‐dioxides III, which are derivatives of the new heterocyclic system thieno[2,3‐ h ]‐1,2‐benzoxathiin. Dehydrogenation with DDQ of cycloadducts IIIa‐d was successful only in the case of IIIa (NR 2 = dimethylamino) to give in low yield 4‐dimethylamino‐3,4‐dihydrothieno[2,3‐ h ]‐1,2‐benzoxathiin 2,2‐dioxide.