Dual reactivity of O-α-allenyl esters under palladium(0) catalysis: From carbopalladation/allylic alkylation domino sequence to decarboxylative allenylation

In a mechanistically-oriented study, O-α-allenyl esters have been evaluated as potential substrates for Pd-catalyzed carbopalladation/allylic alkylation domino sequences and decarboxylative allenylation reactions. The domino sequence turned out to be feasible only with electron-deficient aryl iodides, thereby showing a narrower potential than that previously observed with the malonamide-based series. The decarboxylative allenylation of O-α-allenyl esters was also tested and turned out to be practicable with β-ketoester-based substrates and using specific basic conditions. Plausible reaction mechanisms are proposed to account for the observed reactivities.

O-α-Allenyl esters have been studied as substrates for Pd-catalyzed carbopalladation/allylic alkylation domino sequences and decarboxylative allenylation reactions. The former sequence turned out to be feasible using electron-deficient aryl iodides, while the latter transformation was successful with β-ketoesters and using specific basic conditions.Figure optionsDownload as PowerPoint slideHighlights
► Allenyl malonates and activated aryl halides undergo carbopalladation/allylation.
► Allenyl esters oxidatively add to Pd(0) more readily than the corresponding amides.
► Allenyl β-oxoesters undergo decarboxylative Pd-catalyzed allenylation.