Zn-ProPhenol Catalyzed Enantio- and Diastereoselective Direct Vinylogous Mannich Reactions between α,β- and β,γ-Butenolides and Aldimines

We report a Zn-ProPhenol catalyzed reaction between butenolides and imines to obtain tetrasubstituted vinylogous Mannich products in good yield and diastereoselectivity with excellent enantioselectivity (97 to >99.5% ee). Notably, both α,β- and β,γ-butenolides can be utilized as nucleophiles in this transformation. The imine partner bears the synthetically versatile N-Cbz group, avoiding the use of the specialized aryl directing groups previously required in related work. Additionally, the reaction can be performed on gram scale with reduced catalyst loading as low as 2 mol %. The functional group-rich products can be further elaborated using a variety of methods.