Reaction Steps
Retinyl 2,5-Dimethylbenzyl Ether (3c) was prepared from retinol and 2,5-dimethylbenzyl chloride as outlined by the general procedure. The reaction mixture was stirred at room temperature during 2 hr and at 80° C. during 3 hr. After the crude product had been obtained from the ether extract, successive chromatographic operations were performed on silica gel 60 as follows: flash chromatography with 2:1 chloroform-pentane; flash chromatography with 95:5 cyclohexane-ethyl acetate; gravity chromatography with 97:3 cyclohexane-ethyl acetate. The product obtained by combining the purified specimens from each chromatographic procedure was a syrup: yield, 30%; HPLC (at 340 nm or 254 nm), 100%; MS m/z 404 (M), 285 (C2OF29O), 269 (C20H29), 255 (C19H27), 119 (2,5-dimethylbenzyl); UV λmax326 nm (ε 50 800), 251 (6100); 1H NMR (CDCl3) δ 7.14 (bs, 1H, H6′), 7.04 (bd, 1H, H3′, J3′,4′=7.7 Hz), 7.00 (dd, 1H, H4′, J4′,6′=1.6 Hz), 6.60 (dd, 1H, H11, J10,11=11.1 Hz, J11,12=15.1 Hz), 6.31 (d, 1H, H12), 6.15 (d, 1H, H8, J7,8=16.2 Hz), 6.11 (d, 1H, H7), 6.09 (d, 1H, H10), 5.70 (t, 1H, H14), 4.48 (s, 2H, H21), 4.20 (d, 2H, H15, J14,15=6.8 Hz), 2.31 (s, 3H, CH3), 2.29 (s, 3H, CH3), 2.01 (t, 2H, H14), 1.95 (d, 3H, H19, J10,19=0.6 Hz), 1.85 (bs, 3H, H20), 1.71 (s, 3H, H18), 1.65-1.57 (m, 2H, H3), 1.48-1.44 (m, 2H, H2), 1.02 (s, 6H, H16, H17). Anal. Calcd. for C29H40O: C, 86.08; H, 9.96. Found: C, 85.75; H, 10.32.
