Effect of amine structure and reaction additives on enantioselective deprotonations mediated by homochiral magnesium amide bases

A series of novel, optically pure, Mg-bisamides have been prepared and, in turn, used to mediate enantioselective deprotonations of conformationally locked ketones. The new bases exhibit a wide range of selectivities, from poor to excellent (up to 95:5 e.r.); trends between amine structure and the subsequent selectivity of the deprotonation system are detailed. In addition, the effects on the selectivity and the reactivity of the deprotonation process on replacing the Lewis base additive HMPA for DMPU have been investigated and found to be related to the reaction temperature.