Phosphine-catalyzed enantioselective [4 + 1] annulation of oxindoles with allenic ketones for the construction of spirocyclopentene oxindoles

Abstract

A phosphine-catalyzed enantioselective [4 + 1] annulation between allenic ketones and oxindoles has been developed. This annulation reaction makes use of allenic ketones as dielectrophilic C4 synthons and oxindoles as nucleophilic C1 reaction partners. A range of 3-spirocyclopentene-2-oxindoles with quaternary stereogenic centers were prepared in high yields and with excellent enantioselectivities. Synthetic elaborations of the [4 + 1] annulation product led to a facile total synthesis of (+)-debromoflustramine B.