A mixture of 1,1-dimethylethyl 6-cyano-1-[4-(ethyloxy)-4-oxobutyl]-5-methyl-3,4-dihydro-2(1H)-isoquinolinecarboxylate (Preparation 26; 533 mg, 1.38 mmol), hydroxylamine hydrochloride (575 mg, 8.27 mmol) and sodium bicarbonate (695 mg, 8.27 mmol) in ethanol (15 ml) was stirred at 80° C. for 32 h. More hydroxylamine hydrochloride and sodium bicarbonate (3 equivalent of each) were added, and heating was continued at 80° C. overnight. More hydroxylamine hydrochloride and sodium bicarbonate (3 equivalent of each) were added, and heating was continued at 80° C. for 5.5 h. More hydroxylamine hydrochloride and sodium bicarbonate (3 equivalent of each) were added, and heating was continued at 80° C. overnight. The mixture was cooled to room temperature and the solid was filtered off and washed with ethanol. The filtrate and washings were combined, most of the solvent removed, and the residue dissolved in ethyl acetate. The solution was washed with brine, dried over MgSO4 and concentrated in vacuo to give the title compound (500 mg) as a pale yellow foam.
