the sodium borohydride reduction of 3,5-disubstituted 1,4-dihydro-2,6-dimethyl-4- ( pyridinyl ) pyridines 2 and 5 in the presence of methyl , phenyl , or tert-butyl chloroformate afforded the respective 4- ( dihydropyridinyl ) -1,4-dihydropyridines 4 and 6 in good yield .
C0034255
pyridines
C0012315
dihydropyridines