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(EtOH). IR: 3090, 3060, 1615, 1585, 1545, 1520, 1490, 1370, 1350, 1300, 1190. 1H-NMR (CDCl3): 8.30 (d, CH);
8.57 (dd, CH); 9.03 (d, CH); 9.04 (d, CH); 9.05 (d, CH).
1,4-Diethyl-1,2,3,4-tetrahydro-6-nitroquinoxaline (22). Crude 21 (2.60 g, 14.8mmol) and NaBH 4 (5.62 g,
148mmol) were placed in dioxane (40 ml), and AcOH (25 ml, 0.44 mol) was slowly added under stirring at r.t.
After 1 h at r.t., the mixture was heated to 908. To ensure complete reaction, more NaBH4 (5.62 g, 148mmol)
was added to the hot mixture over a period of 4 h. After altogether 15 h at 908, the product was extracted with
CH2Cl2 and purified by dry-column FC (toluene/acetone mixtures of increasing polarity): 2.90 g (83%) of 22.
M.p. 598. IR: 2972, 2931, 2873, 1576, 1530, 1494, 1372, 1300. 1H-NMR (CDCl3): 1.207 (t, Me); 1.213 (t, Me); 3.29
(t, CH2); 3.37 (q, CH2); 3.44 (q, CH2); 3.51 (t, CH2); 6.43 (d, arom. H); 7.38( d, arom. H); 7.66 (dd, arom. H).
1,4-Diethyl-1,3,4,6-tetrahydro-9-(trifluoromethyl)pyrido[2,3-g]quinoxalin-7(2H)-one (23b). Compound 22
(620 mg, 2.64 mmol) in anh. EtOH (15 ml) was reduced by shaking with H2 (40 psi) at 208 for 20 h in the
presence of 10% Pd/C. The catalyst was removed, the mixture was concentrated, and the air-sensitive
intermediate (6-amino-1,4-diethyl-1,2,3,4-tetrahydroquinoxaline) was reacted with isopropyl 4,4,4-trifluoro-2-
oxobutanoate (790 mg, 4 mmol) in the presence of anh. ZnCl2 (550 mg, 4 mmol) at 1808 for 15 min. Workup by
dry-column FC (SiO2; AcOEt) afforded 630 mg (73%) of 23. M.p. 2558 (CH2Cl2). IR: 2950, 1669, 1528, 1447,
1341, 1255,1159, 1125. 1H-NMR (CDCl3): 1.20 (t, Me); 1.23 (t, Me); 3.28( t, CH2); 3.36 (q, CH2); 3.44 (q, CH2);
3.49 (t, CH2); 6.43 (s, arom. H); 6.39 (s, arom. H); 6.75 (s, arom .H); 12.01 (s, NH). Anal. calc. for C16H18F3N3O:
C 59.07, H 5.58, N 12.92; found: C 59.21, H 5.65, N 12.80.
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