Asymmetric Halo-Mannich-Type Reaction Provides Access to Pyrrolidines and β-Proline Derivatives

A new halo-Mannich-type reaction is reported using cyclopropyl carbonyl-derived enolates and
sulfonyl-protected imines. Chiral oxazolidinones auxiliaries were found to be effective for completely
controlling the stereochemistry of the products. Variations in the oxazolidinone, protecting group,
and imine components show this to be a quite general reaction. The initial iodo-Mannich products
were found to be readily cyclized in the presence of triethylamine to afford the resulting protected
pyrrolidines, which could be readily deprotected under standard conditions.