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

Abstract

<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 <b>1 </b>using <i style="mso-bidi-font-style:normal">m</i>-chloroperbenzoic acid. With this reagent compound <b>1</b>, in methylene chloride, affords olean-2α-epoxy-12-ene-15α-oI <b>3</b> (confirmed by X-ray crystallographic analysis) through the intermediate 2α,14α-diepoxytaraxerane <b>4</b>. The latter <b>4</b> has also been isolated from the same reaction mixture. This backbone rearrangement from the Δ¹⁴-taraxarene skeleton 4 to Δ¹²-0leanane structure <b>3</b>, 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 <b>4.</b> Subsequent opening of the intermediate oxirane at Δ¹⁴therefore must occurr <i>via</i> 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 <b>4</b> also undergoes rearrangement to oIean-12-ene-2α,3β,15α-trioI <b>5 </b>with boron trifluoride etheratein methylene chloride.</span></span></span>