To a cold mixture of 2.0 g (3.5 mmol) of compound 6c, 200 ml of deaerated water and 100 ml of ethyl acetate, 1.14 g (14 mmol) of sodium bicarbonate and 2.43 g (14 mmol) of sodium dithionite were added. The mixture was stirred under N2 for 20 mins. The ethyl acetate layer was separated and the aqueous layer was re-extracted with 100 ml of ethyl acetate. The combined ethyl acetate was washed with cold deaerated water, dried over anhydrous Na2SO4 and distilled on rotovapor. The viscous yellow oily residue was dissolved in 5 ml of acetone, filtered under N2 atmosphere and then evaporated under reduced pressure. The solid residue was dried under vacuum over P2O5 in N2 atmosphere. It reduced alcoholic AgNO3 instantaneously and gave no color with DeCl3 test. Yield, 1.3 g (83%) m.p. 45°-48° C.; UV (CH3OH) 210 and 355 nm; NMR (CDCl3) δ 7.04-6.92 (m, 4H, C6H3 +C2 dihydropyridine proton), 5.71-5.61 (doublet of doublets, 1H, C6 dihydropyridine proton), 4.81 (bs, 1H, CONH), 4.60-4.51 (m, 1H, C5 dihydropyridine proton), 3.53 (q, 2H, J=6.3 Hz, --N--CH2), 2.36 (bs, 2H, C4 dihydropyridine proton), 2.91 (s, 3H, N--CH3), 2.79 (t, 2H, J=6.3 Hz, CH2), 1.33 (s, 18H, CO--C(CH3)3). Anal. Calcd for C25H34N2O5. 11/2H2O: C, 63.9; H, 7.93; N, 5.96. Found: C, 63.4; H, 7.81; N, 5.94.
