合成路线1

The cyclization of (XIV) by means of MeAlCl2 in dichloromethane followed by benzoylation with benzoyl chloride gives a mixture of benzoates (XV) and (XVI) that are separated by chromatography. The desired isomer (XV) (additional (XV) is obtained by isomerization of (XVI) by HCl in hot acetic acid) was selctively methylenated with CH2I2 and Br2Zn in toluene yielding the cyclopropanated compound (XVII). Elimination of the benzoyl group of (XVII) with DIBAL in dichloromethane affords alcohol (XVIII), which is silylated with TBDMS-Cl and imidazole in DMF giving the silyl ether (XIX). The cleavage of the cyclopropane ring of (XIX) with tert-butyl perbenzoate, followed by hydrolysis of the resulting ester yields the methanol derivative (XX), which is selectively reduced with Li in THF/NH3 affording the cis-isomer (XXI). Finally, this compound is oxidized with NaClO4 in tert-butanol, and desilylated with tetrabutylammonium fluoride to give the target oleanolic acid.