Radical Migration–Addition of <i>N</i>-<i>tert-</i>Butanesulfinyl Imines with Organozinc Reagents

Abstract

A novel migration–addition sequence was discovered for the reaction of enantioenriched <i>N</i>-<i>tert</i>-butanesulfinyl iminoacetate <b>1a</b> with functionalized benzylzinc bromide reagents, producing <i>tert</i>-leucine derivatives in excellent diastereoselectivity (dr 98:2). The absolute configurations of two new chiral centers were unambiguously assigned by chemical transformations and X-ray crystallography. In addition, the regio- and diastereoselectivities of this novel reaction were both explained through the key <i>N</i>-sulfinamine intermediate <b>M6</b> generated by the <i>tert</i>-butyl radical attack on the imine. Computational analysis of this reaction process, which was performed at the B3LYP/6-311++G­(3df,2p)//B3LYP/6-31G*-LANL2DZ level, also supported our proposed two-stage mechanism