Phosphine-catalyzed [3 + 2] annulation reaction: highly regio- and diastereoselective synthesis of 2-azaspiro[4.4]nonene-1,3-diones

Abstract

A novel phosphine-catalyzed [3 + 2] annulation of γ-substituted allenoates with succinimides was developed, which was successfully applied to the synthesis of 2-azaspiro[4.4]nonene-1,3-dione derivatives. The reaction afforded the desired products in moderate to high yields (up to 96%) with excellent regioselectivities and diastereoselectivities (up to >99 : 1 dr). A plausible reaction mechanism has also been proposed based on previous literature.