Achievement of ring inversion of myo-inositol derivatives due to silyloxy/silyloxy repulsion enhanced by the trans-substituents on both sides |
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Authors: | Kotaro Okajima Hiroshi Imagawa Mugio Nishizawa |
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Institution: | a School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan b Faculty of Pharmaceutical Sciences, Tokushima Bunri University, 180 Nishihamaboji, Tokushima 770-8514, Japan |
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Abstract: | The introduction of quite bulky trialkyl or diarylalkylsilyl groups into vicinal trans-hydroxy groups induced a conformational flip of certain multifunctionalized cyclohexane rings from the usual chair form possessing more equatorial substituents (equatorial-rich chair form) into another chair-form that has more axial substituents (axial-rich chair form). This realization was experimentally revealed by the conformational study of the synthetic myo-inositol derivatives possessing two tert-butyldimethylsilyl (TBS), two triisopropylsilyl (TIPS), or two tert-butyldiphenylsilyl (TBDPS) groups on an adjacent trans-diol. Among them, the cyclohexane rings of the 4,5-bis-O-TIPS-myo-inositol, 4,5-bis-O-TBDPS-myo-inositol, and 1,2,3,6-tetra-O-benzyl-4,5-bis-O-TBDPS-myo-inositol were in the axial-rich chair form. Comparison of the ring conformations also revealed that the order of the repulsion was OTBDPS/OTBDPS>OTIPS/OTIPS>OTBS/OTBS, and the silyloxy/silyloxy repulsion was enhanced when the two silyloxy groups were placed in the center of the contiguous four equatorial substituents. |
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Keywords: | Ring conformation Myo-inositol Axial-rich chair Silyl protecting groups |
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