Stereoselective Connection of a C<sub>2</sub>- and a Linear C<sub>n</sub>-Unit to a Cyclopropane by a Formal Twofold Nucleophilic Substitution
作者:Elmar Vilsmaier、Thomas Stamm、Gisbert Michels
DOI:10.1055/s-1988-27730
日期:——
Bicyclo[4.1.0]heptan-7-one O,N-acetals such as 7-methoxy-7-morpholinobicyclo[4.1.0]heptane can be easily converted into 7-substituted 7-(2-oxoalkyl)bicyclo[4.1.0]heptanes via a formal twofold nucleophilic substitution. In the first reaction step, the methoxy group of the O,N-acetal is replaced by the 2,2-dimethyl-4,6-dioxo-1, 3-dioxan-5-yl group by reaction with Meldrum's acid; in the second step, the morpholino group is replaced by a 2-oxoalkyl group by reaction with a 2-alkanone or an enamine. The resultant 2,2-dimethyl-4,6-dioxo-5-[7-(2-oxoalkyl)bicyclo [4.1.0]hept-7-yl]-1,3-dioxanes can be selectively reduced to the corresponding 2-hydroxyalkyl derivatives which readily undergo lactone formation with degradation of the Meldrum's acid moiety, or they can be thermally degradated in the presence of morpholine to give 7-(2-oxoalkyl)bicyclo[4.1.0]heptane-7-acetic acid morpholides. Thus, starting from the O,N-acetal, a C2-unit and a linear or cyclic Cn-unit can be stereospecifically introduced into position 7 of the bicyclo[4.1.0]heptane system.
双环[4.1.0]庚烷-7-
酮 O,N-
乙缩醛(如 7-甲
氧基-7-
吗啉基
双环[4.1.0]庚烷)可以通过形式上的两重亲核取代反应轻松转化为 7-取代的 7-(2-
氧代烷基)
双环[4.1.0]庚烷。在第一步反应中,O,N-
缩醛的甲
氧基通过与梅尔德鲁姆酸反应被
2,2-二甲基-4,6-二
氧代-1,3-二
氧杂
环戊烷-5-基取代;在第二步反应中,
吗啉基通过与 2-烷
酮或
烯胺反应被 2-
氧代烷基取代。最后得到
2,2-二甲基-4,6-二
氧代-5-[7-(2-
氧代烷基)双环 [4.1.0]庚-7-基]-1,3-二
氧杂
环戊烷可以选择性地还原成相应的 2-羟烷基衍
生物,这些衍
生物很容易在梅氏酸分子降解后形成内
酯,或者在
吗啉存在下进行热降解,得到 7-(2-
氧代烷基)
双环[4.1.0]庚烷-7-
乙酸吗啉化物。因此,从 O,N-
缩醛开始,一个 C2-单元和一个线性或环状 Cn-单元可以立体定向地引入到
双环[4.1.0]庚烷体系的第 7 位。