STEREOSPECIFIC ALKYLATION OF BENZENE WITH (+)-PROPYLENE OXIDE BY LEWIS ACID CATALYST AND STEREOCHEMISTRY OF RING-OPENING

The alkylation of benzene with (+)-propylene oxide (I) in the presence of Lewis acid gave (+)-2-phenyl-1-propanol (II), and a mixture of (-)-1-halo-2-propanol (III or V) and (+)-2-halo-1-propanol (IV or VI) as the by-products. The reaction was conducted under various conditions. The magnitude of the optical yields of these products suggests that both the alkylation and ring opening proceed with complete inversion of configuration and the most probable mechanism is of the SN2 type, except for the cases of aluminum bromide catalyst and nitromethane solvent. When aluminum bromide was used as catalyst, about 50% racemization in the formation of (+)-II and (+)-VI was observed, and the reaction appears to proceed partially through a carbonium ion mechanism. Experiments showed that the formation of the racemic products was due neither to the racemization of the starting material nor to the racemization of the products. In the case of nitromethane solvent, the ring opening reaction proceeded with retention of configuration. This shows the possibility of SNi process. © 1969.