Tunable Preparation of β‐Substituted Alkenoate Esters via Radical Alkenylation of C(sp3)–H Bonds with Allenoates

Abstract

A photocatalytic strategy for the radical alkenylation of aliphatic C(<i>sp</i>³)–H bonds with 2,3‐allenoate esters is described. The protocol takes place upon irradiation of the reaction mixture in the presence of the decatungstate anion, which triggers C–H cleavage in the chosen aliphatic substrates. The photogenerated C‐centered radicals add regioselectively to the central C(<i>sp</i>)‐atom of the cumulenic structure, delivering an allyl‐type radical adduct that finally leads to the β‐substituted alkenoate ester of interest. When an aliphatic allenoate is adopted, the protocol leads to the selective formation of a β,γ‐alkenoate, while the corresponding phenyl ester delivers a mixture of β,γ‐ and α,β‐alkenoates. Rationalization of the observed regioselectivity is supported by computational work, which highlights how the steric demand of the allenoate ester at the radical adduct level determines the reaction outcome. The versatility of the protocol, which can also take place under (telescoped) flow conditions, is further demonstrated by the possibility to divert the reaction outcome toward the selective formation of β,γ‐ or α,β‐alkenoate esters by performing the photocatalyzed process alone or in combination with a subsequent base‐promoted C=C double bond migration, respectively.