Radical-Mediated C-H Functionalization: A Strategy for Access to Modified Cyclodextrins.
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 C5IIof 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 a1C4conformation. 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.
Síntesis de Productos Naturales, Instituto de Productos Naturales y Agrobiología del CSIC , Carretera de La Esperanza 3, 38206, La Laguna, Tenerife, Spain.
Dimitri
D
Alvarez-Dorta
Síntesis de Productos Naturales, Instituto de Productos Naturales y Agrobiología del CSIC , Carretera de La Esperanza 3, 38206, La Laguna, Tenerife, Spain.
Elisa I
EI
León
WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, Scotland, U.K.
Alan R
AR
Kennedy
Síntesis de Productos Naturales, Instituto de Productos Naturales y Agrobiología del CSIC , Carretera de La Esperanza 3, 38206, La Laguna, Tenerife, Spain.
Angeles
A
Martín
Síntesis de Productos Naturales, Instituto de Productos Naturales y Agrobiología del CSIC , Carretera de La Esperanza 3, 38206, La Laguna, Tenerife, Spain.
Inés
I
Pérez-Martín
Síntesis de Productos Naturales, Instituto de Productos Naturales y Agrobiología del CSIC , Carretera de La Esperanza 3, 38206, La Laguna, Tenerife, Spain.
Ernesto
E
Suárez