Study on the Mechanism of Allylation of Acetophenone Catalyzed by Zinc Amide Model Compound

The reaction mechanism of allylation of acetophenone catalyzed by zinc amide model compound is studied at the M05-2X (SMD, pentane)/6-311++G** level. The calculation result indicates that the non-catalyzed reaction proceeds concertedly via a six-membered-ring transition state, which requires a high energy barrier of 119.7 kJ·mol^-1. In the presence of Zn(HHDS)₂, the reaction takes place via the stepwise mechanism, which involves the B to Zn transmetalation, allylation of acetophenone and the regeneration of Zn(HHDS)₂. The B to Zn transmetalation with an energy barrier of 63.2 kJ·mol^-1 is rate-determining step. The calculation result shows that the formation of the allyl zinc amide species is kinetically more favorable than the generation of diallylzinc species. The recovery of Zn(HHDS)₂ via the cleavage of the B-N bond is 33.9 kJ·mol^-1 lower than the regeneration of the allyl zinc amide species via B to Zn transmetalation in free energy, and Zn(HHDS)₂ is the actual active species in the present system.