View all references Preferential functionalization on the α positions can be achieved by introducing a benzylidene group. During the course of the reaction, the nitrogen atom of the pyridine ring favors the reactivity on the α methyl groups leading to 3 as the major product in the presence of the tribenzylidene derivative (R = CH˭CHPh in Sch. 1) which is difficult to separate from 3. After two successive chromatographies on silica gel, compound 3 was finally obtained ...
