Benzylation of Imines with Activated Boronate Nucleophiles

Benzylation reactions of N-tosylimines and N-tert-butanesulfinyl imines using benzylboronic acid pinacol ester are reported. s-Butyllithium was used to activate the boronic ester, rendering it nucleophilic. The reaction was compatible with electronically diverse substituents on the imine in both substrate classes. Good diastereoselectivity was observed in additions to N-tert-butylsulfinylaldimines. The diastereoselectivity observed in these reactions is consistent with an open transition state for the addition. Examples of a secondary alkylboronic ester nucleophile and a N-tert-butanesulfinyl trifluoromethylketimine electrophile are also included.