Comprehensive Synthesis of Monohydroxy鈥揅ucurbit[n]urils (n = 5, 6, 7, 8): High Purity and High Conversions

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• 作者：Mehmet M. Ayhan ; Hakim Karoui ; Mica毛l Hardy ; Antal Rockenbauer ; Laurence Charles ; Roselyne Rosas ; Konstantin Udachin ; Paul Tordo ; David Bardelang ; Olivier Ouari
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：August 19, 2015
• 年：2015
• 卷：137
• 期：32
• 页码：10238-10245
• 全文大小：588K
• ISSN：1520-5126

文摘

We describe a photochemical method to introduce a single alcohol function directly on cucurbit[n]urils (n = 5, 6, 7, 8) with conversions of the order 95鈥?00% using hydrogen peroxide and UV light. The reaction was easily scaled up to 1 g for CB[6] and CB[7]. Spin trapping of cucurbituril radicals combined with MS experiments allowed us to get insights about the reaction mechanism and characterize CB[5], CB[6], CB[7], and CB[8] monofunctional compounds. Experiments involving ¹⁸O isotopically labeled water indicated that the mechanism was complex and showed signs of both radical and ionic intermediates. DFT calculations allowed estimating the Bond Dissociation Energies (BDEs) of each hydrogen atom type in the CB series, providing an explanation of the higher reactivity of the 鈥渆quatorial鈥?C鈥揌 position of CB[n] compounds. These results also showed that, for CB[8], direct functionalization on the cucurbituril skeleton is more difficult because one of the methylene hydrogen atoms (H_b) has its BDE lowering within the series and coming close to that of H_c, thus opening the way to other types of free radicals generated on the CB[8] skeleton leading to several side products. Yet CB[5]鈥?OH)₁ and CB[8]鈥?OH)₁, the first CB[8] derivative, were obtained in excellent yields thanks to the soft method presented here.