To a stirred solution of cyanomethylphosphonic acid diethyl ester (1.08 ml, 6.86 mmol) in anhydrous THF (10 ml) in an ice bath was added lithium bis-(trimethylsilyl)amide (1.0 M solution in THF, 6.86 ml, 6.86 mmol) slowly. The mixture was stirred at rt for 40 min, before a solution of (2,3-dihydrobenzo[1,4]dioxin-6-yl)-(3,5-dimethoxyphenyl)methanone (1.03 g, 3.43 mmol) in anhydrous THF (20 ml) was added. The mixture was refluxed overnight. The solution was poured into ice water (20 ml) and the two phases were separated. The THF phase was evaporated and combined with the aqueous phase, which were then extracted with CH2Cl2 (2×40 ml), washed with water (50 ml), dried over MgSO4, filtered and concentrated in vacuo to an oil, which was purified via flash column chromatography 5% EtOAc in hexane gradient to 25% EtOAc in hexane) to give 3-(2,3-dihydro-benzo[1,4]dioxin-6-yl)-3-(3,5-dimethoxy-phenyl)-acrylonitrile as an oil (0.98 g, 88%): 1H NMR (DMSO-d6) δ 6.99-6.79 (m, 3H, Ar), 6.65-6.62 (2ts, 1H, Ar), 6.46-6.44 (2ds, 2H, Ar), 6.25 (s, 0.47H, double bond proton of one isomer), 6.20 (s, 0.54H, double bond proton of the other isomer), 4.33-4.24 (m, 4H, 2CH2), 3.76 (s, 3H, OCH3), 3.74 (s, 3H, OCH3); 13C NMR (DMSO-d6) δ 179.5, 160.8, 160.7, 145.7, 144.8, 143.3, 143.0, 140.3, 139.1, 130.4, 129.7, 122.5, 121.7, 118.2, 118.1, 117.9, 117.2, 117.1, 116.6, 107.1, 106.7, 101.8, 100.9, 95.4, 94.3, 64.4, 64.2, 64.0, 64.0, 55.4, 54.9; Anal. Calcd. For C19H17NO4 (+0.05 H2O): C, 69.40; H, 5.26; N, 4.24. Found: C, 69.19; H, 5.11; N, 4.25.
