Radical [3+2] Annulation of 2,8-Alkynones with Sulfur Ylides for the Synthesis of Furo[3,4-c]Quinolin-4(5H)-ones by Dual Photoredox/Copper Catalysis

Furo[3,4-c]quinolin-4(5H)-ones, as a crucial furan-core fused architecture, are extensively distributed in natural products and pharmaceutical agents, demonstrating diverse pharmacological profiles. Herein, a photoredox/copper dual catalytic strategy is reported, enabling the efficient construction of polycyclic furan compounds. A series of independently designed and synthesized precursor compounds containing both 2,8-alkynone and sulfur ylide moieties were subjected to visible light irradiation, through which the [3+2] radical annulation between the activated sulfur ylides and 2,8-alkynones was conducted, affording furo[3,4-c]quinolin-4(5H)-ones in moderate to excellent yields. Sulfur ylide was employed as a reactive radical initiator within the reaction system, which was subsequently eliminated as dimethyl sulfide upon reaction completion. The reaction exhibited excellent substrate compatibility, with both electron-withdrawing groups and electron-donating groups undergoing smooth cyclization, indicating remarkable functional group tolerance. The limitations of conventional furan synthesis, including substrate restrictions and harsh reaction conditions, were effectively addressed. This study established an efficient and straightforward methodology for synthesizing polysubstituted furan derivatives, successfully circumventing the requirement for strongly acidic or basic conditions while proceeding efficiently under mild reaction conditions.