Indole-Fused Benzoxepine Synthesis via Visible-Light-Driven Aerobic Dehydrogenative [5 + 2] Annulation

Abstract

A photocatalyzed oxidative dehydrogenative annulation between 2-(1H-indol-2-yl)­phenols and alkenylphenols is presented. Various indole-fused benzoxepines can be obtained at room temperature using atom-efficient strategies. This method not only avoids the use of stoichiometric amounts of oxidants but also exhibits excellent atom economy by generating H2O as the only theoretical byproduct.

Sustainable Synthesis through Catalyst‐Free Photoinduced Cascaded Bond Formation

“…Liu co‐workers demonstrated the synthesis of indole‐fused benzoxepine 4 c through photochemical aerobic [5+2] annulation (Scheme 4). [18] In contrast to the previously documented method utilizing heavy transition metal catalysts for synthesizing indole‐fused oxepine, [19] the current procedure demonstrates a more environmentally friendly approach induced by visible light, free from both metal and photocatalyst. Under purple LED irradiation, alkenylphenol 4 a and 2‐(1 H ‐indol‐2‐yl)phenol 4 b formed p ‐quinone methide radical 4 i and a phenoxy radical 4 ii via SET with aerobic oxygen.…”