Enantioselective Synthesis of Pyrrolidines by a Phosphine-Catalyzed γ-Umpolung/β-Umpolung Cascade.

Abstract

Herein, we report an enantioselective catalytic annulation of electron-poor allenes with aminocrotonates. The reaction proceeds by the umpolung γ-amination of the allenoate and β-umpolung intramolecular conjugate addition. The reaction provides ready access to pyrrolidines using a homochiral phosphepine catalyst, which allows most products to form in good yields (55-85%) with ≥95:5 er and ≥4:1 dr. An assisted tandem-catalytic variant is also viable, and mechanistic studies supporting the proposed reaction pathway are reported.