Enantioselective Pd-Catalysed Deallylative γ-Lactonisation of Propargyl Carbazolone Allyl Carbonates: Mechanistic Insight into their Decarboxylative Allylation

Subjection of N-methyl carbazolone allyl carbonates bearing a propargyl side chain to Pd0 catalysis leads to the formation of enantioenriched γ-lactones, rather than the expected products of decarboxylative allylation. This side reaction has not been observed with the enantioselective decarboxylative allylation of related β-ketoesters, and provides evidence for a mechanism involving turnover limiting decarboxylation from the palladium carboxylate resting state. Following lactonisation, the Pd0 catalyst is regenerated by PdII reductive alkyne coupling.