Asymmetric Synthesis of Bicyclic Nitrocyclopropanes from Primary Nitro Compounds and Stereoselective Formation of Tetrahydro-2H-cyclopenta[b]furans via Ring Expansion/Cyclization Reaction

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• 作者：Akio Kamimura ; Takaaki Moriyama ; Yuji Ito ; Takuji Kawamoto ; Hidemitsu Uno
• 刊名：Journal of Organic Chemistry
• 出版年：2016
• 出版时间：June 3, 2016
• 年：2016
• 卷：81
• 期：11
• 页码：4664-4681
• 全文大小：596K
• 年卷期：0
• ISSN：1520-6904

文摘

Optically active bicyclic nitrocyclopropanes are readily prepared from primary chiral nitro compounds, prepared by the conjugate addition of propionaldehyde to a nitro alkene in the presence of proline-derived organocatalysts. The one-step cyclopropanation took place smoothly in a highly stereoselective manner regardless of the stereogenic center adjacent to the allylic unit. Although the allylation reaction catalyzed by BF₃·OEt₂ provides a mixture of two possible diastereomers, subsequent oxidation of the alcoholic carbon after the formation of nitrocyclopropanes gave diastereomerically pure single products. As a result, separation of the diastereomers during the reaction sequence is unnecessary. Baeyer–Villiger oxidation of the bicyclic nitrocyclopropane ketones followed by enolization resulted in stereoselective formation of a novel cyclopenta[b]furan ring in good yield via ring expansion followed by transannular nucleophilic cyclization.