Approaches toward the origin of homochirality using the synthetic organic chemistry - Asymmetric autocatalysis with amplification of enantiomeric excess

Asymmetric autocatalysis with amplification of enantiomeric excess is found in the enantiose-lective addition of diisopropylzinc to pyrimidine-5- carbaldehyde using pyrimidyl alkanol as an asymmetric autocatalyst. Asymmetric autocatalysis has been employed as a method for clarifying the origin of homochirality. Circularly polarized light, quartz and statistical fluctuation of enantio-meric imbalance act as chiral triggers for asymmetric autocatalysis to afford highly enantioen-riched products. We have investigated the asymmetric autocatalysis using chiral crystals formed from achiral and racemic compounds as the origins of chirality. Absolute control of the crystal chirality of cytosine was achieved by the removal of crystal water of achiral cytosine monohydrate. Enantioselective carbon-carbon bond formation on the enantiotopic crystal face of aldehyde was established by using the vapor of diisopropylzinc. In addition, asymmetric autocatalysis triggered by chiral compounds arising from H, C and O isotopes substitution has been achieved. Reversal phenomena of enantioselectivity were observed in β-amino alcohol catalyzed dialkylzinc addition to aldehyde by using the mixture of two different β-amino alcohols as chiral ligands.