1977 Volume 50 Issue 12 Pages 3288-3294
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.
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