[CH3:1][S:2][C:3]1[CH:4]=[C:5]2[N:10]([C:11]=1[C:12]([O:14][CH2:15][CH3:16])=[O:13])[CH:9]=[CH:8][CH:7]=[CH:6]2.[N:17]([O-])=[O:18].[Na+].[OH-].[Na+]>C(O)(=O)C.O>[CH3:1][S:2][C:3]1[C:4]([N:17]=[O:18])=[C:5]2[N:10]([C:11]=1[C:12]([O:14][CH2:15][CH3:16])=[O:13])[CH:9]=[CH:8][CH:7]=[CH:6]2A solution of 470 mg (2 mmol) of ethyl 2-(methylsulphanyl)-3-indolizinecarboxylate 9 in 10 ml of acetic acid, stirred at 0° C., was admixed dropwise over 10 minutes with a solution of 165 mg of sodium nitrite in 5 ml of water. The reaction mixture was then left with stirring for a further hour. The acidic phase was basified with a solution of 2N NaOH, and then extracted with dichloromethane (25 ml×3). The organic phase was dried over magnesium sulphate, filtered and then concentrated under vacuum to give ethyl 2-(methylsulphanyl)-1-nitroso-3-indolizinecarboxylate 10 (460 mg). m.p: 134-135° C. 1H NMR (CDCl3): δ 9.58 (d, J=6.8 Hz, 1H), 8.45 (d, J=8.5 Hz, 1H), 7.70 (t, J=8.2 Hz, 1H), 7.20 (td, J=7.0, 1.1 Hz, 1H), 4.50 (q, J=7.1 Hz, 2H), 3.05 (s, 3H), 1.52 (t, J=7.1 Hz, 3H). 13C NMR (CDCl3): 161.2, 156.9, 143.4, 135.7, 127.2, 123.7, 118.7, 118.0, 112.9, 61.2, 19.4, 14.4.
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