合成路线1

Alternatively, condensation of the dienol silyl ether intermediate (XIV) with 2-bromobenzaldehyde dibenzyl acetal (L) by means of t-BuLi in the presence of t-BuMgCl in THF furnishes the expected addition compound (LI).Protection of the vicinal diol moiety of (LI) with trimethyl borate and pyridine in benzene gives the boronic ester (LII), which is cyclized by means of SnCl4 in dichloromethane to yield the tricarbocyclic compound (LIII). Hydrolysis of the boronic ester of (LIII) with pinacol and DMAP in benzene affords the vicinal diol (LIV), which is reduced at the keto group with DIBAL in dichloromethane and silylated at the resulting alcohol with TBDMS-OTf in the same solvent to give the fully protected intermediate (LV). Elimination of the phenylthio group of (LV) by means of Bu3SnH and AIBN in refluxing benzene yields the tricyclic compound (LVI), which is debenzylated with H2 over Pd/C and treated with Swern oxidant to provide ketone (LVII). Selective hydrogenation of (LVII) with potassium in liquid ammonia in the presence of 2,2,4-trimethyl-3-isopropyl-3-pentanol furnishes the dihydro intermediate (LVIII), which is selectively desilylated with TBAF in THF to yield the vicinal diol (LIX). Silylation of diol (LIX) with t-Bu2SiHCl and BuLi in THF affords the cyclic silyl ether (LX), which is reduced at the carbonyl group with NaBH4 and CeCl3 in methanol giving the secondary alcohol (LXI). Finally, this compound is dihydroxylated by oxidation with O2, light and rose bengal as photoinductor to furnish the triol (XXII), already reported.