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Highly β-Selective O-Glucosidation Due to the Restricted Twist-Boat Conformation

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journal contribution
posted on 12.04.2007, 00:00 by Yasunori Okada, Tatsuya Mukae, Kotaro Okajima, Miyoko Taira, Mari Fujita, Hidetoshi Yamada
Ethyl 1-thio-2,3,4,6-tetrakis-O-triisopropylsilyl-β-d-glucopyranoside, ethyl 6-O-benzyl-1-thio-2,3,4-tris-O-triisopropylsilyl-β-d-glucopyranoside, and ethyl 6-O-pivaloyl-1-thio-2,3,4-tris-O-triisopropylsilyl-β-d-glucopyranoside induced highly β-selective O-glucosidations. Among them, the 6-O-pivaloylated substrate provided the best selectivity up to α/β = 3:97 with cyclohexylmethanol, and the substrate was used for glucosidations with secondary and tertiary alcohols in a highly β-selective manner. The selectivity would be caused by the twist-boat conformation of the pyranose; this is the first β-selective O-glucosidation based on conformational control of the pyranose ring.