Cascade Mn‐Mediated γ‐Alkylation/oxa‐Michael Addition of Enones with 1,3‐Dicarbonyls

A radical‐based strategy for regioselective γ‐C?C bond formation/oxa‐conjugate addition, forming the tetrahydrobenzofuran core common to many bioactive natural products is described. The technique utilizes readily available enone derivatives and 1,3‐dicarbonyl compounds as coupling partners in an oxidative formal [3+2] cycloaddition mediated by Mn^III. The transformation delivers polycyclic products in good yields and proceeds with complete regiocontrol and excellent stereoselectivity. Sterically encumbered substrates are notably well‐tolerated and bond formation occurs readily to form neopentyl and all‐carbon quaternary centers in good yields. Several stereo‐ and chemoselective transformations of the products are described.