Synthesis of a new class of chiral aminoalcohols and their application in the enantioselective addition of diethylzinc to aldehydes

Five new aminoalcohols containing a 2,2'-bridged binaphthyl entity were synthesised and applied as auxiliaries in the enantioselective addition of Et2Zn to tell aldehydes. While reactivities were generally high and low concentrations of aminoalcohols were found sufficient to achieve complete conversions (<1 mol%), the observed enantioselectivities were highly dependent upon auxiliary and substrate structure. Up to 97% e.e.s have been observed in the case of aromatic substrates but significantly lower degrees of asymmetric induction were found for aliphatic substrates (up to ca. 60% e.e.). Suggestions concerning the structure of the transition states based on molecular mechanics calculations are presented to rationalise different enantiocontrol. (C) 2000 Elsevier Science Ltd. All rights reserved.