Silver‐Promoted Cascade Reaction of 4‐Hydroxycoumarins with α‐Keto Acids under Microwave Irradiation: One‐Step Construction of Quaternary Stereocenters

A new Ag2O-promoted cascade reaction of 4-hydroxycoumarins with α-keto acids under mircowave irradiation has been developed. The reaction provides an efficient approach to fused chromenes with quaternary stereocenters in 10 min, and gives good yields. Chromene derivatives can be prepared on a gram scale using this method.