Metal‐Free C<i>sp</i>−C<i>sp</i> and C<i>sp</i>−C<i>sp</i>³ Bond Cleavages of <i>N,S</i>‐Enynes toward Thiophene‐Fused <i>N</i>‐Heterocycles

Abstract

Abstract 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 4 H ‐thieno[3,2‐ b ]indoles and thieno[3,4‐ c ]quinoline‐4(5 H )‐thiones through the tunable C sp −C sp and C sp −C sp 3 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(5 H )‐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