Reactions and rearrangements of triterpenoids-3-Epitaraxerol and its transformation products

Abstract

1322-1330<span style="font-size:14.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:#0f0f0f;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">An interesting rearrangement has been observed with 2, 14-taraxeradiene 1 using m-chloroperbenzoic acid. With this reagent compound 1, in methylene chloride, affords olean-2α-epoxy-12-ene-15α-oI 3 (confirmed by X-ray crystallographic analysis) through the intermediate 2α,14α-diepoxytaraxerane 4. The latter 4 has also been isolated from the same reaction mixture. This backbone rearrangement from the Δ14-taraxarene skeleton 4 to Δ12-0leanane structure 3, with C1 5-α-ol<span style="font-size:14.0pt;line-height:115%; font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:#282828;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">,<span style="font-size:14.0pt;line-height:115%; font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:#0f0f0f;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">confirms α-orientation of the epoxy ring formed at Δ14 in 4. Subsequent opening of the intermediate oxirane at Δ14 therefore must occurr via the generation of an incipient carbonium ion at C(14) to allow the migration of C(13)CH3 to C(14) from the same α phase. Compound 4 also undergoes rearrangement to oIean-12-ene-2α,3β,15α-trioI 5 with boron trifluoride etheratein methylene chloride.</span