Reaction Steps
The following procedure requires dark room conditions. To a cooled solution (5° C.) of 6-{2-Azido-5-[2-(4-cyano-5-dicyanomethylene-2,2-dimethyl-2,5-dihydro-furan-3-yl)-vinyl]-phenoxy}-hexanoic acid (0.1 g, 0.21 mmol) in dichloromethane (20 ml) was added N-hydroxysuccinimide (0.027 g, 0.24 mmol) and DCC (0.052 g, 0.25 mmol). The resulting solution was allowed to stir at 5° C. for 2 hours and then at room temperature for 12 hours. The solvent was removed under reduced pressure and the resulting dark red solid was purified by column chromatography (70% EtOAc/30% Hexane) to give 6-{2-azido-5-[2-(4-cyano-5-dicyanomethylene-2,2-dimethyl-2,5-dihydro-furan-3-yl)-vinyl]-phenoxy}-hexanoic acid 2,5-dioxo-pyrrolidin-1-yl ester as a dark red solid (0.084 g, 69%). 1H NMR (400 MHz, CDCl3) δ: 7.60 (d, 1H, J=16.4 Hz), 7.24 (dd, 1H, J=8.4 Hz, J=1.6 Hz), 7.09 (d, 1H, J=1.6 Hz), 7.04 (d, 1H, J=8 Hz), 6.96 (d, 1H, J=16.4 Hz), 4.13 (t, 2H), 2.87 (s, br, 4H), 2.70 (t, 2H, J=7.2 Hz), 1.98 (m, 2H), 1.91 (m, 2H) 1.82 (s, 6H), 1.68 (m, 2H). 13C NMR (400 MHz, CDCl3) δ: 173.50, 169.25, 168.48, 152.61, 146.50, 133.66, 131.19, 123.40, 121.54, 114.10, 112.07, 111.62, 110.83, 110.29, 97.48, 69.18, 30.85, 29.71, 28.34, 26.55, 25.62, 25.22, 24.22. IR (neat): 3321, 2926, 2850, 2361, 2225, 2128, 2094, 1812, 1783, 1733, 1563, 1536, 1497, 1307, 1292, 1186, 1102, 1064, 1046, 849 cm−1.
