Boron trifluoride etherate → benzyl N-(E)-[1-oxo-2-(acetylthiomethyl)-3-(4-methoxylphenyl)propenyl]-beta-alaninate

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Reaction Steps

4.93 g (11.5 mmol) of the (Z) diester obtained in Example 17 (step D) are dissolved in 100 ml of methylene chloride which has been passed over basic alumina. The solution is irradiated for 2.5 h using a Hanovia TQ 150 lamp after having added dropwise 1.53 ml of boron trifluoride etherate solution (11.5 mmol). The solution is then washed with 1N hydrochloric acid solution (twice 80 ml), with saturated sodiumhydrogen carbonate solution (twice 80 ml) and is dried over magnesium sulphate. After filtration and evaporation, 2.56 g of (E) isomer are recovered after flash chromatography. Yield=52% (after flash chromatography, eluent: ether/petroleum ether 65/35) m.p.<50° C. IR (nujol): 3290, 1740, 1690, 1630 cm -1 1H NMR (CDCl3): 7.35 to 7.05 (m, 7H; 6.75 (AB, 2H, J=8 Hz); 6.70 (s, 1H); 6.10 (t, 1H, J=5 Hz); 4.95 (s, 2H); 3.80 (s, 3H); 3.40 (q app, 2H, J app.=6 Hz); 2.45 (t, 2H, J=6 Hz); 2.25 (s, 3H). 13C NMR (CDCl3): 194.8, 171.6; 168.6; 159.4; 135.4; 132.0; 131.6; 129.8; 128.5; 128.2; 128.0; 127.2; 113.6; 66.2; 55.0; 34.6; 33.6; 33.2; 30.4 Microanalysis: C23H25O5NS Calc. % C=64.61 H=5.89 N=3.27 Found. % C=64.17 H=5.91 N=3.48

Provenance & Evidence