A novel synthesis of 23-dihydro-1H-thieno[3,4-b]pyrroles via ring transformation of cyclic sulfonium ylides by titanium(IV) chloride-triethylamine system

Abstract

A series of cyclic sulfonium ylides 4a-h reacted with titanium(IV) chloride in the presence of triethylamine to give the corresponding fused 2,3-dihydro-1H-thieno[3,4-b]pyrroles 5a-h, via a ring opening and recyclization. In contrast, treatment of compounds 4a, 4b, 4e and 4f with titanium(IV) chloride, triethylamine and dimethylamine hydrochloride gave the corresponding thiophenes 6a, 6b, 6e and 6f. Furthermore, compounds 6a and 6b easily underwent cyclization with sodium hydride to afford the corresponding 5a and 5b.