The bromide 13 (807 mg, 1.59 mmol) was dissolved in 20 mL THF/2-methyltetrahydrofuran (1:1) and cooled to −105° C. in a liquid N2/diethyl ether bath. After stirring at −105° C. for 10 min, 4.5 mL of tert-butyllithium (1.1 M in pentanes) was added dropwise. Stirring was continued for another 15 min. 2,7-difluoro-3,6-bis-(2-methoxy-ethoxymethoxy)-xanthen-9-one 9 (912 mg, 2.07 mmol) dissolved in THF (10 mL) was added dropwise to the reaction mixture. The mixture was stirred at −105° C. for 30 min, the cooling bath removed, and the reaction solution was then stirred for an additional 15 min. The resulting mixture was added to 150 mL NH4Cl(sat) and extracted twice with EtOAc. The combined organic layers were washed with brine, dried over Na2SO4 and concentrated in vacuo. The crude product was purified by flash column chromatography, eluting with 50% EtOAc in hexane (with 0.1% Et3N) to yield 956 mg (69%) of 14 as a orange-red oil. Rf=0.33 (in 50% EtOAc/hexane); 1H NMR (300 MHz, CDCl3) δ 7.32-7.27 (m, 5H), 6.97 (d, 2H, J=6.98 Hz), 6.86 (m, 3H), 6.72 (m, 2H), 5.30 (s, 4H), 5.05 (s, 2H), 4.02 (s, 4H), 3.85 (m, 4H), 3.56 (m, 4H), 3.36 (s, 6H), 1.38 (s, 18H); 13C NMR (75 MHz, CDCl3) δ 170.5, 150.8, 149.3, 147.6, 145.6, 145.5, 145.4, 145.2, 140.5, 138.4, 136.9, 128.3, 127.7, 127.5, 119.9, 119.8, 119.3, 118.4, 115.2, 114.9, 113.0, 104.9, 94.5, 81.0, 71.4, 70.6, 69.7, 68.1, 58.9, 54.6, 28.0; 19F NMR (282 MHz, CDCl3) δ −139.0 (dd, 2 F); mass spectrum, calculated for C46H55F2NO13 (MH+) 868.4, Found 867.8.
