Triethylamine → ethyl 3-amino-5({[(1S)-2-(dimethylamino)-1-phenylethyl]hydroxy}carbonyl)-6,6-dimethyl-5,6-dihydropyrrolo[3,4-c]pyrazole-1(4H)-carboxylate

Participants

Reaction Conditions

Reaction Steps

To a stirred solution of (S)-2-dimethylamino-1-phenyl-ethanol (68b, 21.50 g, 130.0 mmol) in 1,2-dichloroethane (500 mL) was added triethylamine (26.30 g, 260.0 mmol) and 4-nitrophenyl chloroformate (68c, 27.00 g, 130.0 mmol) at room temperature under nitrogen. The solution was stirred at 50° C. overnight. A total of 16.8 g (130.0 mmol) of Hünig's base was then added, followed by ethyl 3-amino-6,6-dimethyl-5,6-dihydropyrrolo[3,4-c]pyrazole-1(4H)-carboxylate dihydrochloride salt (54a, 17.90 g, 60.25 mmol). The reaction mixture was stirred at 50° C. for another 12 h. It was diluted with dichloromethane (1.5 L) and washed with water (2×1.0 L) and brine (1.0 L), dried over Na2SO4. Another batch with the exact scale was also carried out. These two batches were combined together during workup. Filtration and evaporation followed by flash chromatography (4.75% MeOH/0.25% NEt3/95% DCM) afforded compound 68e ethyl 3-amino-5({[(1S)-2-(dimethylamino)-1-phenylethyl]hydroxy}carbonyl)-6,6-dimethyl-5,6-dihydropyrrolo[3,4-c]pyrazole-1(4H)-carboxylate as a light-yellow gummy oil (5.00 g, 10%). 1H NMR (CDCl3, a mixture of rotamers, only the chemical shifts of the major form is reported) δ: 1.45 (t, J=7.1 Hz, 3H), 1.63 (s, 3H), 1.72 (s, 3H), 2.29 (s, 3H), 2.36 (s, 3H), 2.55-2.63 (m, 1H), 2.88 (dd, J=13, 8.3 Hz, 1H), 4.29 (q, J=13 Hz, 1H), 4.51 (q, J=7.1 Hz, 2H), 5.44 (d, J=10.7 Hz, 1H), 5.8-5.95 (m, 1H), 7.25-7.42 (m, 5H). LCMS (APCI, M+H+) 416.

Provenance & Evidence