Substituent effects on the enantioselective hydrocyanation of aryl aldehydes

A detailed study of the dipeptide catalysed enantioselective hydrocyanation of a series of O-substituted 4-hydroxybenzaldehydes has shown that adverse steric effects can occur leading to low enantiomeric excess (e.e.) values when the substituent is long and flexible. Similar hydrocyanation of several derivatives of 3,4-dihydroxybenzaldehydes have been shown to give very variable values of e.e. Hydrocyanation of 3,5-dimethoxy and 3,4,5-trimethoxybenzaldehyde consistently gave low values of e.e.