Photoredox Ni-catalyzed Branch-Selective Reductive Coupling of Aldehydes with 1,3-Dienes

We report here a Ni-catalyzed reductive coupling of aldehydes with widely available 1,3-dienes under visible light photoredox dual catalysis. The homoallyic alcohols are obtained in broad scope with complete branched regioselectivity. Hantzsch ester is used as the hydrogen radical source to oxidize low-valent nickel salt affording Ni−H species. Preliminary mechanistic studies indicate a successive single-electron transfer (SET) pathway and the generation of a key π-allylnickel intermediate via Ni−H insertion of 1,3-diene in this synergistic catalytic process.