A round bottom flask was flamed to sterilize and product 16 (386 mg, 0.70 mmol) was added and dissolved in THF (5.6 mL). A 1M solution of NaOMe in MeOH was prepared and then added the room temperature solution. The solution was then placed in a 45° C oil bath for 2 hours. For another hour, a 1M NaOH solution (1.4 mL, 1.4 mmol, 2 eq) was slowly added and stirred. During this reaction, the presence of starting material was monitored by TLC. Afterwards, the reaction was cooled until it reached room temperature, upon which, diluted EtOAc (10 mL) was added. Then, the reaction was quenched with 3M HCl (3M). The product was extracted in 10 mL of water and then ethyl acetate (4 x 5 mL). The organic layer was washed with brine (10 mL) and then dried over sodium sulfate. Finally, the product was concentrated in vacuo, producing product 18 in sufficient purity (light yellow foam, 368 mg, 98%).

A PDF of experimental with reagents and techniques can be downloaded here.

​Physical state: white foam; Rf = 0.84 (silica gel, EtOAc); LCMS (m/z): calcd for C31H24N2O7, [M+H]+, 537.2; found, 537.2; IR (film) νmax: br 2923, br 1680, 1527, 1488, 1250, 1038, 730 cm-1; 1H NMR (400 MHz, CDCl3): δ 9.98 (s, 1 H), 8.80 (dd, J = 7.3, 1.8 Hz, 1 H), 8.60 (dd, J = 4.1, 1.8 Hz, 1 H), 8.17 (d, J = 8.2 Hz, 1 H), 7.59 – 7.48 (m, 2 H), 7.42 (dd, J = 8.3, 4.3 Hz, 1 H), 6.97 (dd, J = 4.2, 1.6 Hz, 2 H), 6.93 – 6.81 (m, 2 H), 6.76 (dd, J = 15.6, 8.0 Hz, 2 H), 6.63 (d, J = 15.8 Hz, 1 H), 6.27 (dd, J = 15.8, 7.3 Hz, 1 H), 5.93 (d, J = 5.4 Hz, 4 H), 4.03 (t, J = 9.7 Hz, 1 H), 3.59 (dd, J = 17.4, 8.5 Hz, 1 H), 3.18 (t, J = 9.6 Hz, 1 H), 3.15 (t, J = 9.7 Hz, 1 H).  13C NMR(1:1 MeOD:CDCl3, 101 MHz): δ 174.5, 170.8, 147.7, 147.7, 147.5, 146.9, 146.3, 137.6, 136.4, 134.6, 133.3, 131.4, 130.8, 127.7, 126.9, 126.7, 121.9, 121.3, 120.8, 119.6, 116.8, 107.8, 107.7, 107.0, 105.2, 100.7, 100.6, 50.8, 47.5, 42.5, 42.2. 

Gutekunst, W. R.; Gianatassio, R.; Baran, P. S. Angew. Chem. Int. Ed. 2012, 51, SI-6-7.