Triethylamine → Ethyl 2-methylaminoindolizine-3-carboxylate

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A mixture of 1-ethoxycarbonylmethylpyridinium bromide 5 (1 g, 4.1 mmol), 1,1-bismethylthio-2-nitroethene (1.2 g; 8.1 mmol) and Et3N (4.1 g, 40.6 mmol) in ethanol (30 mL) was heated at reflux for 12 h. The solvents and the triethylamine were then evaporated under vacuum. The oil obtained was extracted with water (50 mL) and toluene (3×50 mL). The combined extracts were dried over anhydrous magnesium sulphate, filtered and then concentrated under vacuum. The residue was chromatographed on a column of silica with an elution gradient of 1/1 to 4/1 of ethyl acetate/petroleum ether. This gave 0.5 g of ethyl 2-methylaminoindolizine-3-carboxylate 6 in the form of an oil. 1H NMR (DMSO-d6) δ: 9.11 (br s, 1H), 7.32 (d, J=8.8 Hz, 1H), 7.07-7.01 (m, 1H), 6.71-6.66 (m, 1H), 5.88 (br s, 1H), 5.85 (s, 1H), 4.32 (q, J=7.0 Hz, 2H), 2.85 (d, J=5.1 Hz, 3H), 1.34 (t, J=7.0 Hz, 1H), 13C NMR (CDCl3) δ: 161.0, 148.9, 138.2, 127.0, 123.4, 115.8, 109.9, 98.6, 84.3, 58.7, 31.0, 14.7.

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