Fe/S cluster catalyzed cascade cyclization of N,S-1,6-enynes for the synthesis of thieno[3,4-b]indoles†

Fe/S cluster catalyzed radical cascade cyclization of alkylthio-functionalized o-anilide-embedded N,S-1,6-enynes to afford thieno[3,4-b]indoles is developed. The cycloisomerization strategy offers a straightforward route to 4H-thieno[3,4-b]indoles through the 1,2-sulfur transfer and Csp³–S bond cleavage, with the formation of both an indole ring and a fused thiophene ring in one pot. In this cascade, the element sulfur acts as the oxidant to induce the single electron transfer (SET) process.