30 アノメリック炭素上でのカルバニオン転位による糖質の新変換法(口頭発表の部)

抄録

Carbohydrates are inexpensive and frequently easy to obtain in the pure form, thus they are widely used as chiral blocks for various natural product synthesis. They are also used as the chiral auxiliaries for asymmetric synthesis . Among the chiral centers on carbohydrates, the anomeric carbon has special characteristics, i. e., it is easily epimerable and its stereochemistry is controlled by the anomeric effect and steric effect of other chiral centers. Here we wish to report new conversion methods of carbohydrates based on carbanion rearrangements at anomeric centers. 1)Asymmetric transmission from the anomeric center of glucose via [2,3]-Wittig rearrangement In the interest of using the anomeric center of carbohydrates as the chiral source and developing a new type of conservative asymmetric synthesis in the [2,3]-Wittig rearrangement, we have undertaken a project to investigate the [2,3]-Wittig rearrangement of a glucose derivative. The rearrangement of glucose derivative 1 was carried out under the standard conditions. The rearrangement was found to proceed with a high degree of diastereoselectivity. 2) [1.2]-Wittig rearrangement of acetal systems and its application to C-glycosydation. Despite the great potential of the [1,2]-Wittig rearrangement as a tool for the conversion of an ether bond to a C-C bond, its synthetic use has been extremely limited so far. To use this rearrangement for practical C-C bond formation, we attempted the Wittig rearrangement of cyclic acetal systems. Upon treatment with BuLi, cyclic acetals which were prepared from lactol and benzylalcohol or (E)-3-trimethylsilyl-2-propene-1-ol underwent highly stereoselective rearrangements affording products in good yield. The application of the present Wittig variants of acetal systems to C-glycosylation will be presented.