Reaction Steps
(5Z,7E,22E)-9,10-Secocholesta-5,7,10(19),22-tetraen-3α-ol (5) A solution of compound (4) (100 mg, 0.26 mmol) in ether (120 ml)-benzene (30 ml) mixture was degassed with argon for 40 min. The solution was irradiated at 0° C. for 13 min in a quartz immersion well equipped with UV lamp and filter. The solvent was removed under reduced pressure and the residue separated by HPLC, using 1% 2-propanol in hexane as eluent to obtain the pure previtamin D derivative (40.4 mg, 40%) which was collected at 24 ml; NMR δ 0.72 (3H, s, 18-H3), 0.87 (6H, d, J=6.7 Hz, 26-H3 and 27-H3), 1.04 (3H, d, J=6.8 Hz, 21-H3), 1.65 (3H, s, 19-H3), 3.91 (1H, m, 3-H), 5.28 (2H, br m, 22-H and 23-H, 5.50 (1H, m, 11-H), 5.69 and 5.96 (2H, AB q, J=12.5 Hz, 7-H and 6-H); UV λmax 260.5 nm; λmin 234 nm. The previtamin (40 mg, 0.1 mmol) in ethanol (100 ml) was heated under reflux for 3 h. After removal of solvent, the product mixture was separated by HPLC (elution with 1% 2-propanol in hexane). The yield of the vitamin (5) (collected at 34 ml) was 30.8 mg (77%) mp (hexane) 99°-101° C.; NMR δ 0.56 (3H, s, 18-H3), 0.88 (6H, d, J=6.7 Hz, 26-H3 and 27-H3), 1.02 (3H, d, J=6.6 Hz, 21-H3), 3.96 (1H, m, 3-H), 4.82 and 5.05 (2H, each narr. m, 19-H2), 5.27 (2H, br m, 22-H and 23-H), 6.03 and 6.24 (2H, ABq, J=11.4 Hz, 7-H and 6-H; UV λmax 265 nm, λmin 228 nm; IR: 3420,1458,1441,1378,1366,1050,970,943,891,862 cm-1 ; mass spectrum, m/e (M+, 22), 349 (M+ -H2O-Me, 4), 271 (M+ -side chain, 8), 253 (M+ -side chain-H2O, 13), 136 (100), 118 (80).
