The (E)- and (Z)-isomers (2E and 2Z) of 3-O-benzyl-5,6-dideoxy-1,2-O-isopropylidene-α -d-xylo-hept-5-eno-1,4-furanose were subjected to Claisen rearrangement with triethyl orthoacetate. Possible two diastereomers were obtained as a 1 to 1 mixture from both of 2Z and 2E, and also from their 3-hydroxy or 3-siloxy derivatives. On the other hand, the rearrangement of the corresponding d-ribo derivative (13Z) and its 3-O-(t-butyldiphenylsilyl) derivative proceeded with a high level of diastereoselectivity. By contrast, the (E)-isomer of 13Z showed no significant stereoselectivity, resulting in the formation of a diastereomeric mixture. The configurations of the introduced stereogenic centers by the rearrangements were unambiguously established by chemical transformations.
3-O-苄基-5,6-二脱氧-1,2-O-异亚丙基-α-d-
呋喃木-5-烯糖-1,4-糖的(E)和(Z)异构体(2E和2Z)与三乙基
原甲酸酯进行了克莱森重排反应。从2Z和2E以及它们的3-羟基或3-
硅氧基衍
生物中,得到了可能的两种非对映异构体的1:1混合物。另一方面,相应的d-
呋喃核糖衍
生物(13Z)及其3-O-(叔丁基二苯基
硅基)衍
生物的重排反应具有高度的非对映选择性。相比之下,13Z的(E)异构体显示出较弱的立体选择性,形成了非对映异构体混合物。通过
化学转化明确确定了重排引入的手性中心的构型。