Allyl ketene acetal Claisen rearrangement of urinoc acid derivatives with furanoside structure was studied. Reproducibility of the observed stereodiscrimination was confirmed in the conversion of enantiomeric starting materials. From X-ray structural data of the major reaction product obtained from a cis-pentenyl uronate, the transition state was proven to preferentially adopt a chair-like geometry. Alterations in the protecting group pattern led to a significant decrease in total yields. Use of β-deoxygenated starting material allowed a greater extent of variation, but was accompanied by the total loss of stereodiscrimination. For the first time, the reaction was applied to pyranoid starting material structures. The conversion of a gluco-configurated compound remaining unsuccessful, with the corresponding galacto and 4-deoxy derivatives an interesting stereoselectivity could be observed. This was lost by further structural simplification to a 1,4-dideoxypyranoid ring. This way, however, a substantial improvement in yield could be achieved.
研究了具有
呋喃糖苷结构的
尿囊酸衍
生物的
烯丙基
乙缩醛克莱森重排。在对映体起始材料的转化过程中,观察到的立体区分的可
重复性得到了证实。从顺式
戊烯基
尿苷酸的主要反应产物的 X 射线结构数据来看,过渡态被证明优先采用椅子状几何结构。保护基团模式的改变导致总产率显著下降。使用δ-
脱氧起始原料可以实现更大范围的变化,但同时也完全丧失了立体区分性。该反应首次应用于
吡喃起始原料结构。
葡萄糖构型化合物的转化仍未成功,但相应的半
乳糖和 4-
脱氧衍
生物却出现了有趣的立体选择性。如果进一步将结构简化为 1,4-二
脱氧吡喃环,这种立体选择性就会消失。不过,通过这种方法,可以大大提高产率。