A theoretical and experimental study of the asymmetric addition of dialkylzinc to N-(diphenylphosphinoyl)benzalimine

The mechanism of the enantioselective addition of diethylzinc to N(diphenyl phosphinoyl)benzalimine with catalysis by bicyclic 2-azanorbornyl-3-methano ls was studied by quantum chemical calculations. The mechanism proved to di ffer from that of the addition of diethylzinc to aldehydes and also from an earlier proposed mechanism. The results of the calculations were used to i dentify several factors responsible for the selectivity. The theoretical ev aluation was performed in connection with an experimental study of the effe cts of introducing an additional stereocenter in the ligand. An efficient r oute to both diastereomers of new bicyclic 2-azanorbornyl-3-methanols with an additional chiral center (the secondary alcohol group) is also presented . In the best case, an enantiomeric excess of up to 97% was obtained with t hese new ligands.