Visible Light-Promoted Ring-Opening Alkenylation of Cyclic Hemiacetals through β-Scission of Alkoxy Radicals

The chemistry of alkoxy radicals was extensively explored during the period of 1960s to 1990s, but it has remained dormant for the past few decades. Recently, alkoxy radicals attract the attentions again, because new methods for generating alkoxy radical species have emerged. These newly developed methods are mainly based on the photolysis by visible light under mild conditions, thus allowing for new transformations of the carbon-centered radical species that are generated from the beta-scission or hydrogen abstraction of the alkoxy radicals. Herein, we demonstrate that the alkoxy radicals derived from cyclic hemiacetals can be generated through visible-light-induced electron transfer with sodium iodide and triphenylphosphine as the catalyst. The alkoxy radicals subsequently undergo beta-scission to generate carbon-centered radicals, which are trapped by cinnamic acids, aryl alkenes, vinylboronic acid and silyl enol ether to deliver the corresponding C-C bond forming products. This catalytic method for ring-opening alkenylation reaction of cyclic hemiacetal derivatives under visible-light irradiation conditions demonstrates the compatibility of the visible light-promoted alkoxy radical generation method with various carbon radical trapping processes. This work opens up new possibilities for the application of alkoxy radicals in organic synthesis.