Abstract
A simple and efficient radical C–H functionalization to access modified cyclodextrins (CDs) has been developed. The well-defined conformation of glycosidic and aglyconic bonds in α-, β-, and γ-CDs favors the intramolecular 1,8-hydrogen atom transfer (HAT) promoted by the 6I-O-yl radical, which abstracts regioselectively the hydrogen at C5II of the contiguous pyranose. The C5II-radical evolves by a polar crossover mechanism to a stable 1,3,5-trioxocane ring between two adjacent glucoses or alternatively triggers the inversion of one α-d-glucose into a 5-C-acetoxy-β-l-idose unit possessing a 1C4 conformation. The 6I,IV- and 6I,III-diols of α- and β-CDs behave similarly to the monoalcohols, forming mostly compounds originating from two 1,8-HAT consecutive processes. In the case of 6I,II-diols the proximity of the two 6-O-yl radicals in adjacent sugar units allows the formation of unique lactone rings within the CD framework via a 1,8-HAT−β-scission tandem mechanism. X-ray diffraction carried out on the crystalline 1,4-bis(trioxocane)-α-CD derivative shows a severe distortion toward a narrower elliptical shape for the primary face.
Original language | English |
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Pages (from-to) | 11766-11787 |
Number of pages | 22 |
Journal | Journal of Organic Chemistry |
Volume | 81 |
Issue number | 23 |
DOIs | |
Publication status | Published - 2 Nov 2016 |
Keywords
- C–H functionalization
- modified cyclodextrins
- aglyconic bonds
- glycosidic bonds
- polar crossover mechanism
- elliptical