Functionalization of trans-decalin. II. A synthesis of dl-isopetasol from trans-5-oxodecalin-8a,2-carbolactone.
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概要
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A stereocontrollcd synthesis of <I>dl</I>-isopetasol (<B>1a</B>) from <I>trans</I>-5-oxodecalin-8a,2-carbolactone (<B>2a</B>) is described. The key intermediate, <I>trans</I>-5,5-ethylenedioxy-1β,8aβ-dimethyldecalin-2-one (<B>7b</B>) was prepared by reductive methylation of <I>trans</I>-5,5-ethylenedioxydecahydrocyclopropa[<I>d</I>]naphthalen-2-one (<B>5</B>) for introducing the vicinal two methyl groups at C-1 and C-8a carbon atoms. The cyclopropyl ketone <B>5</B> was obtained by reduction of the acetal of <B>2a</B> followed by (1) tosylation of the primary alcohol, (2) oxidation of the secondary alcohol with Corey's NCS–DMS reagent, and (3) cyclization with <I>t</I>-BuOK. Reduction of <B>5</B> with lithium in liquid ammonia provides initially the corresponding enolate anion, which can be trapped with methyl iodide to give <I>trans</I>-5,5-ethylenedioxy-1α,8aβ-dimethyldecalin-2-one (<B>7a</B>), smoothly. Epimerization of <B>7a</B> with MeONa in MeOH gave the desired intermediate <B>7b</B>. Reduction of <B>7b</B> with lithium in liquid ammonia gives the 2α-alcohol <B>8b</B>, stereoselectively. The conversion of <B>8b</B> into <B>1a</B> was carried out as follows: (1) deacetalization of <B>8b</B> followed with acetylation, giving trans-6α-acetoxy-4aβ,5β-dimethyldecalin-1-one (<B>9b</B>); (2) reduction of <B>9b</B> with NaBH<SUB>4</SUB> and subsequent dehydration affording the olefinic acetate <B>11</B>; (3) oxidation of <B>11</B> with CrO<SUB>3</SUB>–pyridine complex, giving the enone <B>12</B>; (4) aldol condensation of <B>12</B> with acetone followed by dehydration, isomerization of double bond, and hydrolysis, providing the desired <B>1a</B>.
- 公益社団法人 日本化学会の論文
著者
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Torii Sigeru
Department Of Applied Chemistry Faculty Of Engineering Okayama University
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Inokuchi Tsutomu
Department Of Applied Chemistry Faculty Of Engineering Okayama University
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Inokuchi Tsutomu
Department of Industrial Chemistry, School of Engineering, Okayama University
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Kawai Kiyoto
Department of Industrial Chemistry, School of Engineering, Okayama University
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