Pyridine Derivatives from Vinylic Phosphazenes via an aza-Wittig Reaction

Significance

The use of N-vinylic phosphazenes for the regioselective synthesis of dihydropyridines and pyridines is reported. Reactions of unsubstituted methyl or phenylvinylketones (R⁶ = H, equation 1) produced substituted pyridines in poor to excellent yields following quinone or benzoquinone oxidation of the precursor 1,4-dihydropyridine derivatives. Reactions involving electron-deficient vinyl ketones (equation 2) produced a variety of 1,4-dihydropyridines in moderate to good yields, which were not further oxidized. Overall, a fairly large substrate scope was achieved. The synthetic utility of this methodology was illustrated by the synthesis of the biologically active calcium channel blocker nitrendipine A (D. F. Babcock and co-workers J. Biol. Chem. 2000, 275, 21210).