Radical-polar crossover allenylation of alkenes: Divergent synthesis of homoallenic alcohols and amides

We report the first example of intermolecular allenyl functionalization of alkenes by a radical-polar crossover process. This reaction leads to homoallenic alcohols and amides with high synthetic value. It is initiated by the addition of an allenyl radical to an alkene, a challenging step because of the short lifetime of the allenyl radical and its strong tendency to produce propargyl radicals. The electrophilicity of transient allenyl radicals can be efficiently improved by a strategically located sulfone, an outcome that is supported by density functional theory calculations. Solvents are engaged as nucleophiles in this radical-polar crossover, and the products can be converted to diversely complex molecules. This reaction proceeds under mild photoredox neutral conditions and shows exclusive regioselectivity, broad functionality tolerance, and high product diversity.