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 syn thesised and applied as auxiliaries in the enantioselective addition of Et2 Zn to tell aldehydes. While reactivities were generally high and low concen trations of aminoalcohols were found sufficient to achieve complete convers ions (<1 mol%), the observed enantioselectivities were highly dependent upo n auxiliary and substrate structure. Up to 97% e.e.s have been observed in the case of aromatic substrates but significantly lower degrees of asymmetr ic induction were found for aliphatic substrates (up to ca. 60% e.e.). Sugg estions concerning the structure of the transition states based on molecula r mechanics calculations are presented to rationalise different enantiocont rol. (C) 2000 Elsevier Science Ltd. All rights reserved.