Intramolecular Bromonium Ion Assisted Epoxide Ring-Opening: Capture of the Oxonium Ion with an Added External Nucleophile

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• 作者：Karl J. Bonney ; D. Christopher Braddock ; Andrew J. P. White ; Muhammad Yaqoob
• 刊名：Journal of Organic Chemistry
• 出版年：2011
• 出版时间：January 7, 2011
• 年：2011
• 卷：76
• 期：1
• 页码：97-104
• 全文大小：930K
• 年卷期：v.76,no.1(January 7, 2011)
• ISSN：1520-6904

文摘

9-Oxabicyclo[6.1.0]non-4-ene (1) undergoes intramolecular bromonium ion-assisted epoxide ring-opening using N-bromosuccinimide via a presumed oxonium ion that is subject to stereospecific, nonregioselective capture with added external nucleophiles producing novel bicyclo[4.2.1] and bicyclo[3.3.1] ethers. Carboxylic acids (as catalyzed by tetramethylguanidine), alcohols, water, and halides can all function as effective nucleophiles. Stereospecific direct opening of the bromonium ion with carboxylic acids was found to be a competing process where high dilution disfavors this pathway. Halogen-induced isotopic ¹³C NMR shifts (螖未 CBr 1.3鈭?.9 ppb; 螖未 CCl 8.6鈭?.7 ppb) were found to be most useful in unambiguously identifying halogen-bearing carbons, and correlation of these ¹³C NMR shifts allowed ready assignment of diastereomeric structures. The structure of adducts 6b, 6c, 7b, 7c, 7d, and 8a鈭?b>d were all elucidated by X-ray crystallography.