Synthesis of 8-membered tetrahydroazocines via manganese-mediated regioselective sulfonylation/cyclization of N-substituted enamides with sodium sulfinites

Abstract

Intermolecular radical cascade cyclization of tethered alkynes involving the cracking of aryl or vinyl C(sp²)–H has become an important pathway for the synthesis of benzene-fused or CC bond-containing heterocyclic building blocks. While major progress has been made in the construction of 5–7-membered heterocycles, the construction of 8-membered heterocycles such as tetrahydroazocines has remained elusive and challenging. Herein, we report the manganese-mediated sulfonylation/cyclization of N-substituted enamides to synthesize 8-membered tetrahydroazocines, involving chemoselective sulfonyl radical addition to the C–C triple bond and 8-endo-trig cyclization.