Selective hydrolysis of the acetate ester from oleanoic acid derivative (I) by means of methanolic KOH afforded alcohol (II), which was oxidized to the corresponding ketone (III) with Jones reagent. Claisen condensation of (III) with ethyl formate in the presence of NaOMe produced ketoaldehyde (IV). Isoxazole derivative (V) was then obtained by cyclization of (IV) with hydroxylamine. Subsequent cleavage of the isoxazole ring of (V) with sodium methoxide gave rise to keto nitrile (VI). The title alpha,beta-unsaturated nitrile was then obtained by conversion of (VI) to the phenylselenyl derivative (VII), followed by oxidation with H2O2 and elimination of the resulting selenoxide.

Hydrolysis of the acetate ester from oleanoic acid derivative (I) by means of methanolic KOH afforded alcohol (II). Subsequent Jones oxidation of (II) yielded the corresponding ketone (III) (1). This was condensed with Stiles' reagent in DMF, followed by esterification with diazomethane to produce ketoester (IV). The required alpha,beta-unsaturated ester (VI) was then obtained by conversion of (IV) to the phenylselenyl derivative (V), followed by oxidation with H2O2 and elimination of the resulting selenoxide. Finally, partial hydrolysis of (VI) with KOH furnished the title carboxylic acid.

Selective hydrolysis of the acetate ester from oleanoic acid derivative (I) by means of methanolic KOH afforded alcohol (II), which was oxidized to the corresponding ketone (III) with Jones reagent. Claisen condensation of (III) with ethyl formate in the presence of NaOMe produced ketoaldehyde (IV). Isoxazole derivative (V) was then obtained by cyclization of (IV) with hydroxylamine. Subsequent cleavage of the isoxazole ring of (V) with sodium methoxide gave rise to keto nitrile (VI). The title alpha,beta-unsaturated nitrile was then obtained by conversion of (VI) to the phenylselenyl derivative (VII), followed by oxidation with H2O2 and elimination of the resulting selenoxide.

Hydrolysis of the acetate ester from oleanoic acid derivative (I) by means of methanolic KOH afforded alcohol (II). Subsequent Jones oxidation of (II) yielded the corresponding ketone (III) (1). This was condensed with Stiles' reagent in DMF, followed by esterification with diazomethane to produce ketoester (IV). The required alpha,beta-unsaturated ester (VI) was then obtained by conversion of (IV) to the phenylselenyl derivative (V), followed by oxidation with H2O2 and elimination of the resulting selenoxide. Finally, partial hydrolysis of (VI) with KOH furnished the title carboxylic acid.

Selective hydrolysis of the acetate ester from oleanoic acid derivative (I) by means of methanolic KOH afforded alcohol (II), which was oxidized to the corresponding ketone (III) with Jones reagent. Claisen condensation of (III) with ethyl formate in the presence of NaOMe produced ketoaldehyde (IV). Isoxazole derivative (V) was then obtained by cyclization of (IV) with hydroxylamine. Subsequent cleavage of the isoxazole ring of (V) with sodium methoxide gave rise to keto nitrile (VI). The title alpha,beta-unsaturated nitrile was then obtained by conversion of (VI) to the phenylselenyl derivative (VII), followed by oxidation with H2O2 and elimination of the resulting selenoxide.

Formylation of methyl 3-oxooleanolate (I) with ethyl formate and NaOMe afforded the (hydroxymethylene)derivative (II). The unsaturated aldehyde (IV) was prepared by selenylation of (II) with phenylselenyl chloride and pyridine, followed by oxidation of the resulting selenide (III) with H2O2 with concomitant elimination of the resulting selenoxide. Jones oxidation of aldehyde (IV) afforded carboxylic acid (V). Finally, hydrolysis of the hindered methyl ester group of (V) was achieved by treatment with lithium iodide in refluxing DMF.