Asymmetric Autocatalysis: The Soai Reaction, an Overview

Asymmetric autocatalysis of 5-pyrimidyl alkanol, 3-quinolyl alkanol, and 5-carbamoylpyridyl alkanol is described in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde, quinoline-3-carbaldehyde, and 5-carbamoylpyridine-3-carbaldehyde, respectively. Significant amplification of enantiomeric excess from extremely low (ca. 0.00005%) ee to near enantiopure >99.5% ee is observed along with the formation of the product. Asymmetric autocatalysis with amplification of ee has been invoked in several theories of the origins of homochirality. Circularly polarized light, chiral inorganic crystals such as quartz, chiral organic crystals composed of achiral compounds such as glycine, spontaneous absolute asymmetric synthesis without the intervention of any chiral factor, and chiral hydrogen (D/H), carbon (13C/12C), nitrogen (15N/14N), and oxygen (18O/16O) isotopomers were found to act as chiral triggers, i.e., the origin of chirality, in asymmetric autocatalysis to afford highly enantioenriched compounds.