Oxidative diphosphonylation of 1,4-dihydropyridines and pyridinium salts

[GRAPHICS] An oxidative double phosphonylation of dihydropyridines 1 and pyridinium sa lts 2 is achieved through the use of dialkyl phosphites, DDQ, and triethyla mine. Acceptable to good yields of 2,6-diphosphonylated-1,2-dihydropyridine s 3 are obtained in a one pot reaction involving tandem nucleophilic additi on/oxidation processes. Isomerization of 3 to the more stable 2,4-diphospho nylated-1,4-dihydropyridine 4 was observed in some cases.