Studies on K[sub 2]CO[sub 3]-Catalyzed 1,4-Addition of 1,2-Allenic Ketones with Diethyl Malonate: Controlled Selective Synthesis of β,γ-Unsaturated Enones and α-Pyrones.

The K[sub 2]CO[sub 3] (10 mol %)-catalyzed 1,4-addition reaction of diethyl malonate with various substituted 1,2-allenic ketones leading to polyfunctionalized β,γ-unsaturated enones 3 or 4 was studied. With 3-unsubstituted 1-substituted-1,2-allenyl ketones, the highly selective formation β,γ-unsaturated enones 4 was observed; with 1,2-allenyl ketones bearing one or two 3-substituents in the allenyl group, only β,γ-unsaturated enones 3 with an unmigrated carbon-carbon double bond were produced; with 3-monosubstituted-1,2-allenyl ketones Z-β,γ-unsaturated enones 3 were formed with excellent stereoselectivity (E:Z > 96:4); with propadienyl ketones, mixtures of β,γ-unsaturated enones 3 and 4 were formed, α-Pyrone derivatives were synthesized via the K[sub 2]CO[sub 3]-catalyzed or -promoted reaction of 1,2-allenic ketones with diethyl malonate via a sequential Michael addition carbon-carbon double bond migration-lactonization process. [ABSTRACT FROM AUTHOR]