In organic chemistry, the Soai reaction is the
alkylation of pyrimidine-5-carbaldehyde with
diisopropylzinc. The reaction is
autocatalytic and leads to rapidly increasing amounts of the same
enantiomer of the product. The product pyrimidyl alcohol is chiral and induces that same chirality in further catalytic cycles. Starting with a low
enantiomeric excess ("ee") produces a product with very high enantiomeric excess.[1] The reaction has been studied for clues about the origin of
homochirality among certain classes of
biomolecules.[2]
The Japanese chemist
Kensō Soai (1950–) discovered the reaction in 1995.[3][4] For his work in "elucidating the origins of chirality and homochirality", Soai received the
Chemical Society of Japan award in 2010.[5]
Other chiral additives can be used as the initial source of
asymmetric induction, with the major product of that first reaction being rapidly amplified. For example, Soai's group has demonstrated that even chiral
quaternary hydrocarbons, which have no clear
Lewis basic site for binding the nucleophile, are nonetheless capable of inducing asymmetric catalysis in the reaction.[6]
The chiral induction is believed to occur as a result of interactions between the C–H bonds of the alkane and the
pi electrons of the aldehyde.[6]
In another example, Soai and coworkers showed that even [15N](2R, 3S)-bis(dimethylamino)butane, whose chirality results solely due to the difference between 14N and 15N (7% isotopic mass difference), gave 45% ee when used as a stoichiometric ligand.[7]
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abKawasaki T, Tanaka H, Tsutsumi T, Kasahara T, Sato I, Soai K (May 2006). "Chiral discrimination of cryptochiral saturated quaternary and tertiary hydrocarbons by asymmetric autocatalysis". Journal of the American Chemical Society. 128 (18): 6032–3.
doi:
10.1021/ja061429e.
PMID16669661.
Micskei K, Rábai G, Gál E, Caglioti L, Pályi G (July 2008). "Oscillatory symmetry breaking in the Soai reaction". The Journal of Physical Chemistry B. 112 (30): 9196–200.
doi:
10.1021/jp803334b.
PMID18593153.