Effect of pressure on sterically congested cyanoalkylation reactions of alcohols

The pressure effect on the phosphine-catalyzed nucleophilic addition of alcohols to unsaturated nitriles is examined. As a general result, pressure promotes these reactions. Their sensitivity to pressure increases with increasing steric congestion of either the alcohol or the nitrile. Activation volumes are found to be very negative pointing not only to a late transition state, but essentially to a considerable electrostriction contribution depending on steric hindrance to ionization. This means that pressures favors formation of the carbanion and attack of the nitrile. The results highlight the synthetic utility of high pressure to remove steric inhibition.