Enantioselective [3 + 3] Annulation-Deoxalation Strategy for Rapid Access to δ-Oxoesters via N-Heterocyclic Carbene Catalysis.

A new and unprecedented stereoselective synthetic approach to δ-oxoesters derivatives from readily available starting materials has been developed. This method, catalyzed by N-heterocyclic carbene, involves an annulation-deoxalation reaction of alkynyl aldehydes with 2,4-diketoesters and proceeds via the chiral α,β-unsaturated acylazolium intermediates. The annulation includes the formation of dihydropyranones, which undergo ring-opening methanolysis with Lewis acid activation, followed by deoxalation to afford chiral 1,5-ketoesters in moderate to good yields.