Metal‐Free Csp−Csp and Csp−Csp3 Bond Cleavages of N,S‐Enynes toward Thiophene‐Fused N‐Heterocycles

Abstract

AbstractAlkylthio‐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−Csp3 bond cleavages of the N,S‐1,6‐enynes, forming both a N‐heterocycle and a fused thiophene ring. The five‐ring π 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.magnified image