Access to 4‐Membered Heterocycles via Visible‐Light Triggered Intramolecular Cyclization from Alkynes: Bypassing Unfavorable 4‐endo‐dig Cyclization

Abstract

We describe a catalyst, oxidant, and coupling-reagent free strategy to access 4-membered heterocycles, representing a unique example of visible-light triggered intramolecular cyclization of propargylic alcohols and amines to access oxetanones and azetidinones respectively. Despite the direct 4-endo-dig cyclization from these starting materials has proven to be unfavorable, the formation of key p-quinone methide intermediacy allows an efficient bypass for regioselective 4-exo-trig cyclization, resulting in the formation of the desired 4-membered heterocycles. This mild and operationally simple protocol facilitates the synthesis of products with distinct substitution patterns such as quaternary alpha-carbons, and enables late-stage functionalization.