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.