Sodium borohydride reduction of adducts of primary amines with aldehydes and p-thiocresol. The alkylation of heterocyclic and aromatic amino-compounds

p-Nitroaniline, 2-aminopyridine (1a), 4-aminopyridine (2a), 2-amino-4-methylpyrimidine (8a), 2-aminothiazole (10a), and 2-aminobenzimidazole (12a) react with aqueous formaldehyde and p-thiocresol in ethanol or methanol solution to give N-(p-tolythiomethyl) derivatives [corresponding to the general formula (4; R2= H)], usually in high yields. When the latter compounds are heated, under reflux, with an excess of sodium borohydride in ethanol or 1,2-dimethoxyethane solution, the corresponding methylamino-compounds [general formula (5; R2= H)] are obtained. By a similar two-step procedure in which aqueous formaldehyde is replaced, as appropriate, by anhydrous acetaldehyde, propionaldehyde, or benzaldehyde, p-nitroaniline is converted into N-ethyl-p-nitroaniline, p-chloroaniline is converted into p-chloro-N-(n-propyl)aniline, (1a) is converted into the corresponding ethylamino- and benzylamino-compounds (1c) and (1d), respectively, and (10a) and (12a) are converted into their 2-N-(n-propyl) derivatives (10c) and (12c), respectively.