Visible-light-mediated decarboxylative ()-alkenylation of aliphatic carboxylic acids with aryl styryl sulfones under metal-free conditions.

The decarboxylative alkenylation of aliphatic carboxylic acids with aryl styryl sulfones is efficiently catalyzed by riboflavin tetraacetate under visible light irradiation at room temperature. This metal-free protocol is cost-efficient, environmentally friendly and provides the corresponding olefins with excellent ()-diastereocontrol. The methodology can also be used to prepare internal alkynes regioselectively by using alkynyl sulfones as radical acceptors. The suitability as building blocks of the olefins obtained was demonstrated by performing an ()- to () photoisomerization, an iron-catalyzed allylic substitution of the phenoxy group derived from the 2-phenoxycarboxylic acid substrates, as well as -epoxidations, and diastereoselective intramolecular iodoarylations. Based on control experiments and DFT calculations, we proposed a reaction mechanism that accounts for the regio- and diastereo-selectivity observed.