Journal
YAKUGAKU ZASSHI-JOURNAL OF THE PHARMACEUTICAL SOCIETY OF JAPAN
Volume 138, Issue 1, Pages 19-25Publisher
PHARMACEUTICAL SOC JAPAN
DOI: 10.1248/yakushi.17-00188
Keywords
spirocyclopropane; ring-opening; cyclization; indole; benzofuran; sulfonium salt
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Funding
- Grants-in-Aid for Scientific Research [15K07853] Funding Source: KAKEN
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This review describes our recent efforts to develop efficient methods for the synthesis of heterocyclic compounds, such as indoles and benzofurans, employing ring-opening cyclization of cyclohexane-1,3-dione-2-spirocyclopropanes, which were prepared by the reaction of 1,3-cyclohexanediones with sulfonium salts. Ring-opening cyclization of cyclohexane-1,3-dione-2-spirocyclopropanes with primary amines proceeded at room temperature to provide 2-substituted tetrahydroindol-4 (5H) -ones in good to excellent yield. The obtained product was readily converted into a 2-substituted 4-hydroxyindole derivative. Furthermore, acid-catalyzed ring-opening cyclization of cyclohexane-1,3-dione-2-spirocyclopropanes proceeded smoothly at room temperature to provide 2-substituted tetrahydrobenzofuran-4 (2H) -ones in excellent yield. The obtained product was converted into a 2-substituted 4-hydroxybenzofuran derivative. The synthetic utility of this catalytic protocol was demonstrated by the total synthesis of cuspidan B.
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