Stereoselective Monoalkylation of α-Halocyclopropyllithiums. A Versatile Method for the Synthesis of α-Alkylcyclopropyl Acetates and Alkylidenecyclopropanes
作者:Katuzi Kitatani、Tamejiro Hiyama、Hitosi Nozaki
DOI:10.1246/bcsj.50.3288
日期:1977.12
The title carbenoids (7 and 8) prepared by the action of butyllithium on dihalocyclopropanes are smoothly methylated with methyl iodide. The product ratio of cis-methylated product (3)/trans-methylated one (4) (or endo-methylated product (5)/exo-methylated one (6) is found to depend on the aging period of the carbenoids; thermodynamic equilibration gives almost 3 or 5. This procedure has been extended to general alkylation by utilizing HMPA co-solvent. The resulting α-alkylated cyclopropyl halides are converted into allylic acetates or cyclopropyl acetates upon acetolysis and also into alkylidenecyclopropanes upon base treatment. The protonolysis of 8 gives trans- or exo-bromocyclopropanes stereoselectively.
通过二卤环丙烷与丁基锂作用制备的碳宾(7和8)能顺利地用甲基碘进行甲基化。顺式甲基化产物(3)/反式甲基化产物(4)(或内型甲基化产物(5)/外型甲基化产物(6)的产率比取决于碳宾的老化时间;热力学平衡几乎给予3或5。该方法已通过利用六甲基磷酰胺(HMPA)作为共溶剂扩展到一般烷基化。得到的α-烷基化环丙基卤代物在乙酰解后转化为烯丙基乙酸酯或环丙基乙酸酯,并且在碱处理下转化为烷基亚甲基环丙烷。8的质子分解选择性地得到反式或外型溴代环丙烷。