There are several synthetic pathways leading to title compound which are depicted in Scheme. Generally, 1-alkyl-4,4 diphenylpiperidines Iike budipine are accessible in a simple manner and with attractive yields by a regioselective reaction of piperidine derivatives such as (I), (II), (III) or, par ticularly, 3-aroyl-4-aryl-4-hydroxypiperidines (IV) with benzene under Friedel Crafts' conditions.
Condensation of 2-mercaptobenzothiazole (I) with isonicotinic acid hydrazide (INH) (II) in the presence of formaldehyde affords H-15 in 80% yield.