Facile Synthesis of γ-Butenolides and Maleic Anhydrides via Annulation of α-Keto Acids and Triazenyl Alkynes.

A facile synthesis of γ-butenolides and maleic anhydrides via annulation of α-keto acids and triazenyl alkynes is described. In this process, α-keto acids and triazenyl alkynes could undergo a self-catalyzed annulation at room temperature to deliver γ-butenolides efficiently, while the further addition of BF3-Et2O furnished maleic anhydrides. Overall, these processes have mild reaction conditions, broad scope, and high efficiency.