Efficient Access to All‐Carbon Quaternary and Tertiary α‐Functionalized Homoallyl‐type Aldehydes from Ketones

Abstract

Abstract β,γ‐Unsaturated aldehydes with all‐carbon quaternary or tertiary α‐centers were rapidly assembled from ketones through a unique synthetic operation consisting of 1) C 1 homologation, 2) Lewis acid mediated epoxide–aldehyde isomerization, and 3) electrophilic trapping. The synthetic equivalence of a vinyl oxirane and a β,γ‐unsaturated aldehyde is the key concept of this previously undisclosed tactic. Mechanistic studies and labeling experiments suggest that an aldehyde enolate is a crucial intermediate. The homologating carbenoid formation plays a critical role in determining the chemoselectivity.