Radical‐Mediated 1,2‐Formyl/Carbonyl Functionalization of Alkenes and Application to the Construction of Medium‐Sized Rings

Abstract A novel radical 1,2‐formylfunctionalization of alkenes involving 1,2(4,5)‐formyl migration triggered by addition of various carbon‐ and heteroatom‐centered radicals to alkenes has been developed for the first time, thus providing straightforward access to diverse β‐functionalized aldehydes with good efficiency, remarkable selectivity, and excellent functional group tolerance. Analogous transformations mediated by a keto‐carbonyl migration have also been effected under similar conditions. This method was used to access ring systems including various benzannulated nine‐, ten‐, and eleven‐membered rings, complex 6‐5(6,7)‐6(5) fused rings, and bridged rings with diverse functionalities.