Studies on K₂CO₃-Catalyzed 1,4-Addition of 1,2-Allenic Ketones with Diethyl Malonate: Controlled Selective Synthesis of β,γ-Unsaturated Enones and α-Pyrones

The K2CO3 (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 of 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 K2CO3-catalyzed or -promoted reaction of 1,2-allenic ketones with diethyl malonate via a sequential Michael addition−carbon-carbon double bond migration−lactonization process

K₂CO₃-Catalyzed Michael Addition−Lactonization Reaction of 1,2-Allenyl Ketones with Electron-Withdrawing Group Substituted Acetates. An Efficient Synthesis of α-Pyrone Derivatives

α-Pyrone derivatives were synthesized via the base catalyzed or promoted reaction of 1,2-allenyl ketones and electron-withdrawing group substituted acetates. The reaction was believed to proceed through a Michael addition C−C double-bond migration−lactonization process