General procedure for the synthesis of 3-amino-5,6,7,8-tetrahydro-6-methyl-1,6-naphthyridine from 6-methyl-3-nitro-5,6,7,8-tetrahydro-6-methyl-1,6-naphthyridine: To a mixture of ethanol (35 mL) and 2-methyltetrahydrofuran (35 mL) of intermediate 128 (1.50 g, 7.76 mmol) was added palladium/carbon catalyst ( 10 wt.%) (826.24 mg, 0.77 mmol) and the reaction mixture was stirred under hydrogen atmosphere for 2 hours. After completion of the reaction, the mixture was filtered through a diatomaceous earth pad and the filter cake was washed with ethanol. The filtrate was concentrated under reduced pressure to give 1.33 g of Intermediate 129, which crystallized on standing (quantitative yield, 95% purity based on 1H NMR analysis, yellow oily).
