Visible light-mediated organocatalyzed 1,2-sulfonylation/acylation cascade of allenes for stereodefined tetrasubstituted alkenes

Abstract

Stereodefined tetrasubstituted alkenes are privileged structural motifs widely found in pharmaceuticals, functional materials, and synthetic intermediates. However, the direct, modular, and stereocontrolled assembly of these skeletons from simple precursors remains a formidable challenge. Herein, we report a visible light-mediated N-heterocyclic carbene (NHC) and photoredox synergistic catalysis for the 1,2-sulfonylacylation of allenes, enabling efficient access to a diverse array of stereodefined fluorinated tetrasubstituted alkene derivatives. This transformation proceeds under mild conditions with broad substrate scope, excellent functional group tolerance, and high regio- and E/Z selectivity (up to >19 : 1). Mechanistic studies reveal a radical pathway involving regiospecific addition of an in situ generated monofluoromethylsulfonyl radical (CH₂FSO₂˙) to the allene, forming an allylic radical intermediate, which subsequently undergoes stereoselective radical-radical coupling with an NHC-stabilized ketyl radical. The E/Z selectivity is governed by the Curtin–Hammett principle, as supported by density functional theory (DFT) calculations. Gram-scale synthesis and diverse downstream transformations demonstrate the practical utility of this method. This work provides a new strategy for the synthesis of stereodefined tetrasubstituted alkenes and expands the frontiers of NHC/photoredox cooperative catalysis in radical cascade reactions.