Asymmetric Mannich-Type Addition of Ketene Silyl Acetals and Thioacetals to N,N-Dialkylhydrazones

ABSTRACT The choice of the 2,6-diphenylpiperidine moiety as the N,N-dialkylamino auxiliary in simple aliphatic dialkylhydrazones and the use of scandium triflate as the catalyst in aqueous media appear as the key strategies that enable the highly diastereoselective nucleophilic addition of ketene silyl acetals and thioacetals. The reaction proceeds to afford the expected adducts in high yields (88-98%) and diastereomeric ratios of up to 99:1. N-N bond cleavage of adducts affords enantiomerically pure β-amino esters.