Reaction Steps
Although a low yield of impure XXVIII can be obtained directly by heating XXVI and XXVII in DMF at 100° for 70 hr., it is better to do the esterification and furan ring closure in separate steps. 65 mg XXVI (0.1 mmole), 50 mg ethyl 4-bromomethylbenzoate (XXVII), 0.2 g K2CO3, and 10 mg tetrabutylammonium hydrogen sulfate were stirred overnight under reflux in acetonitrile. The product, the 4-ethoxycarbonylbenzyl ether of XXVI, was isolated by preparative layer chromatography with petroleum ether-ethyl acetate 1:1, giving 57 mg, 71% yield, m.p. 109°-110°. NMR (CDCl3, 90 MHz) 10.34, s, 1H; 8.06, d, 8 Hz, 2H; 7.47, d, 8 Hz, 2H; 7.3, s, partly obscured by CHCl;3; m, 6.8-6.55, 3H; 6.3, s, 1H; 5.16, s, 2H; 4.37, q, 7 Hz, 4.21, s, 4.14, s, 4.05, q, 7 Hz, 4.02, q, 7 Hz, total 22H; 2.23, s, 3H; 1.38, t, 7 Hz, 1.17, t, 7 Hz, 1.15, t, 7 Hz, total 15H. 39 mg of this ether (0.05 mmole) was stirred with potassium fluoride/alumina reagent (see reference 22) in 1 ml dimethylformamide for 2 hrs. at 150°. The fluorescent product was isolated in 21 mg (54%) yield by preparative layer chromatography on silica with toluene-ethyl acetate 1:1. More prolonged reaction times in DMF lead to increasing ester hydrolysis. NMR (CDCl3, 90 MHz): 8.15, d, 9 Hz, 7.89, d, 9 Hz, total 4-5H; 7.15-7.05, m, 6.78, m, total 6-7H; m, 3.9-4.5, 20-22H; 2.23, s, 3H; 1.0-1.4, m, 13-17H.
