A photocatalytic electron-rich acceptor-involved EDA complexes for Markovnikov addition of alkynes with N-sulfonyl-azoles

Abstract

As a potent approach, electron donor–acceptor (EDA) photochemistry offers prospects for new radical transformations under mild reaction conditions. Current EDA strategies commonly use electron-rich molecules as electron donors and electron-poor molecules as electron acceptors to promote radical-trapping reactions. Due to the charge effect, electron-rich molecules are difficult to use as electron acceptors, greatly limiting the types and applicability of the reactions. We herein describe a terminal alkyne-involved ternary EDA complex strategy to activate electron-rich azoles serving as electron acceptors for the unprecedented Markovnikov addition of alkynes. The electron-deficient terminal alkynes are used as “electron bridges” to efficiently form ternary EDA complexes with electron-rich donors (sodium sulfinates) and electron-rich acceptors (N-sulfonyl-azoles). Detailed investigations of the reaction mechanism reveal that sulfonyl radicals are rapidly formed through the promotion of a photocatalyst-enhanced single-electron transfer (SET) process in EDA complexes, yielding the desired compounds in up to 88% isolated yield with high (E)-configuration selectivity and high N²-regioselectivity. The developed method also has a wide range of substrate scope, providing a simplified and environmentally friendly approach for the rapid preparation of various challenging conjugated α-sulfonyl-β-triazole olefin compounds. This work provides some insight into the development of electron-rich EDA-enabled radical reactions.