Photocatalytic delayed hydration by alkene-alkene coupling: Modular access to highly substituted γ- and δ-lactones.

γ- and δ-lactones are important core structures in a wide range of natural products and bioactive molecules. However, a gap remains for rapid access to γ- and δ-lactones from easily available and simple starting materials with tunability for substitution patterns. Here, a photocatalytic "streamlined sew" strategy of two alkenes with water for the synthesis of γ- and δ-lactones by a [1 + 2 + 2] or [1 + 2 + 3] cyclization has been developed. The reaction features the delayed hydration of alkenes by differentiating different alkyl radicals to undergo chemo- and regioselective alkene-alkene cross-coupling. Notably, styrenes, tetra-, tri-, and disubstituted aliphatic alkenes are tolerated in the reaction, allowing for rapid and modular assembly of γ- and δ-lactones from two alkenes in the presence of water.