Stereocontrol in diels—alder cycloaddition to unsaturated sugars: reactivities of cis-dienophiles with cyclopentadiene
作者:Derek Horton、Dongsoo Koh、Yasushi Takagi
DOI:10.1016/0008-6215(93)84005-q
日期:1993.12
dienophile and give only the endo product. The same sequence starting from L-arabinose gave the enantiomer (7) of 3. In contrast, a related cis-dienophile (9) having a butenolide ring reacts with cyclopentadiene from the opposite (re) face giving mainly the endo adduct (5S,6R)-6-endo-(2,3,4-tri-O-acetyl)-D-arabino-tetritol-1-yl)bicycl o [2.2.1]hept-2-ene-5-endo-carboxylic acid 1,4-lactone (10), isolated
环戊二烯与D-阿拉伯糖衍生的顺-dienophile的环加成,甲基(Z)-4,5,6,7-四-O-乙酰基-2,3-二脱氧-D-阿拉伯糖基庚二烯酸(2 ),在热条件下基本生成单一的降冰片烯加合物,分离出的晶体收率为81%,通过NMR光谱和X射线晶体学鉴定为(5R,6S)-6-内-(1,2,3,4-四甲基) -O-乙酰基-D-阿拉伯糖醇-四糖醇-1-基)bic yclo [2.2.1]-庚-2-烯-5-内-羧酸盐(3)。二烯仅从亲二烯体的表面添加并且仅给出内产物。从L-阿拉伯糖开始的相同序列得到的对映异构体(7)为3。相反,具有丁烯内酯环的相关顺式-二烯亲和体(9)与来自另一面(re)的环戊二烯反应,主要得到内加合物(5S, 6R)-6-内-(2,3,4-三-O-乙酰基)-D-阿拉伯糖醇-四醇-1-基)二环[2.2。1]庚-2-烯-5-内羧酸1,4-内酯(10),分离出的晶体产率为70%,其结