Propose a synthesis for the antihistamine \(p\)-methyldiphenhydramine, given this retrosynthetic analysis. Is \(p\)-methyldiphenhydramine chiral? If so, how many of the possible stereoisomers are formed in this synthesis?

Based on the retrosynthetic analysis provided, the starting materials should be benzophenone and p-methylaniline.

To synthesize p-methyldiphenhydramine from benzophenone and p-methylaniline, we can use the reductive amination reaction. This involves the following steps: 1. Forming an imine: Benzophenone can react with p-methylaniline in the presence of an acid catalyst (such as HCl or p-toluenesulfonic acid) to form an imine, an intermediate compound with a C=N double bond. 2. Reducing the imine: Sodium cyanoborohydride (NaBH3CN) can reduce the C=N bond in the imine intermediate, resulting in p-methyldiphenhydramine. The overall reaction can be represented as follows: Benzophenone + p-methylaniline -> Imine intermediate -> p-methyldiphenhydramine.

p-methyldiphenhydramine has one chiral carbon (also known as a stereocenter) connected to the attached ethylamine moiety. This means there are two possible stereoisomers: R-p-methyldiphenhydramine and S-p-methyldiphenhydramine. However, the stereoselectivity in the synthesis depends on the reductive amination conditions. If there is no chiral control, both R and S stereoisomers will be formed in a racemic mixture (equal mix of both stereoisomers). In summary, the proposed synthesis of p-methyldiphenhydramine is a two-step process involving the formation of an imine intermediate and subsequent reduction with sodium cyanoborohydride. p-methyldiphenhydramine is chiral, and in this synthesis, without chiral control, both R and S stereoisomers will likely be formed.