Phosphine-Catalyzed [3+2] and [2+4] Annulations of gamma-Methyl Allenoates with Aryl alpha-Keto Esters: Stereoselective Syntheses of Functionalized Tetrahydrofurans and 4-Chromanols

摘要

Phosphine-catalyzed [3+2] and [2+4] annulation reactions of gamma-methyl allenoates with aryl alpha-keto esters are described. Under the catalysis of triarylphosphine, gamma-methyl allenoates participate in both the [3+2] annulation with aroylformates and [2+4] annulation with ortho-hydroxy aroylformates smoothly to bring about functionalized tetrahydrofurans and 4-chromanols, respectively, in moderate to excellent yields with high stereoselectivity. The reactions herein also represent rare successful examples of phosphine-catalyzed allene-ketone transformations, and further expand the scope of ketones in allene chemistry under phosphine catalysis.