Mechanism of the Conversion of Inverted CB[6] to CB[6]

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• 作者：Simin Liu ; Kimoon Kim ; Lyle Isaacs
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：August 31, 2007
• 年：2007
• 卷：72
• 期：18
• 页码：6840 - 6847
• 全文大小：439K
• 年卷期：v.72,no.18(August 31, 2007)
• ISSN：1520-6904

文摘

D=jo071034tn00002>Inverted cucurbit[n]urils (iCB[n]) form as intermediates during the synthesis of cucurbit[n]urils fromglycoluril and formaldehyde in HCl (85 deg.gif">C). Product resubmission experiments establish that thediastereomeric iCB[6] and iCB[7] are kinetic products that are less stable thermodynamically thanCB[6] or CB[7] (>2.8 kcal mol^-1). When iCB[6] or iCB[7] is heated under aqueous acidic conditions,a preference for ring contraction is noted in the formation of CB[5] and CB[6], respectively. Interestingly,under anhydrous acidic conditions ring size is preserved with iCB[6] delivering CB[6] cleanly. To establishthe intramolecular nature of the iCB[6] to CB[6] conversion under anhydrous, but not aqueous, acidicconditions we performed crossover experiments involving mixtures of iCB[6] and its ¹³C=O labeledisotopomer ¹³C₁₂-iCB[6]. An unusual diastereomeric CB[6] with a Möbius geometry (13) is proposed asa mechanistic intermediate in the conversion of iCB[6] to CB[6] under anhydrous acidic conditions. Theimproved mechanistic understanding provided by this study suggests improved routes to CB[n]-typecompounds.