Metal-Free Csp-Csp and Csp-Csp(3) Bond Cleavages of N,S-Enynes toward Thiophene-Fused N-Heterocycles

摘要

Alkylthio-functionalized, o-anilide-embedded enynes, that is, N,S-1,6-enynes, were efficiently reacted with elemental sulfur to afford thiophene-fused N-heterocycles. The one-pot sulfur incorporation/cascade cyclization strategy offers a straightforward route to 4H-thieno[3,2-b]indoles and thieno[3,4-c]quinoline-4(5H)-thiones through the tunable Csp-Csp and Csp-Csp(3) bond cleavages of the N,S-1,6-enynes, forming both a N-heterocycle and a fused thiophene ring. The five-ring systems azacyclopenta[f,g]tetracene scaffolds were also obtained from the cascade cyclization of 2-halogen-functionalized thieno[3,4-c]quinoline-4(5H)-thiones. The present synthetic protocol avoids use of prefunctionalized indole and thiophene derivatives as the building blocks for the construction of thiophene-fused N-heterocycles under metal-free conditions.