Asymmetric autocatalysis: product recruitment for the increase in the chiral environment (PRICE).
Asymmetric catalytic reactions are possible via efficient transfer of the chiral environment of a reaction to the transition state. In theory any asymmetric structure may contribute to this, including the product of the reaction itself. For product influence to be significant, a nonlinear effect needs to operate, whereby one diastereomer of the product/catalyst assists the reaction, and the other does not. When these conditions are satisfied, we obtain an asymmetric autocatalytic reaction in which the enantiomeric excess of a compound (that is both product and catalyst) actually increases as the reaction iterates. It is only recently that we have seen reports of such processes. Of particular interest are Soai's reports of the alkylation of aromatic heterocycles. Such reactions, aside from their inherent interest, may offer clues into the origins of asymmetric molecular replication that predated the origin of life.
Todd
Matthew H
MH
Department of Chemistry, Queen Mary, University of London, Mile End Road, London, UK E1 4NS. M.H.Todd@qmul.ac.uk