Cyclopropyl bromides reduction

Cyclopropyl carbanions are capable of maintaining their configuration whereas the CT-radical has been shown to reach inversion equlibrium with a rate constant of lO" s". ITie cyclopropyl bromide 13, and the corresponding iodide, are reduced in a single two-electron polarographic wave and the S +)-isomer yields the R(-)-hydrocarbon with 26% enantiomeric excess [67, 68]. Such a substantial retention of configuration during reduction of the carbon-bromine bond indicates a very fast second electron transfer process. Results from reduction of the cyclopropyl bro-... 

Aliphatic and alicyclic iodides and bromides are reduced at room temperature, while the aromatic, vinyl, and cyclopropyl bromides as well as the chlorides can be reduced only under reflux. For example, the selective reductions shown in Figure... 

The bromide was prepared from the cyclopropyl earblnol obtained by reduction and fxotu the halide a Grignard compound was formed. This/compound treated with formaldehyds gave among other products cydobutylcarblspl.8 Whether this is to be attributed to isomerization or to the presence of cyclobutanol in the cycloprop>l alcohol is uncertain. 

The unusual structure of cycloclavine as the first known pentacyclic clavine alkaloid was derived from physical data (mass spectrum M+ 238 NMR signals of the cyclopropyl methylene group = 0.46 and 1.60) and some chemical transformations (hydrogenation, reductive ring opening, and quaternization). The remaining details of its constitution were finally determined by an X-ray analysis of the metho-bromide. Thus it was shown that the chirality of 11 is 5B, 8R, 10R. 

Isopropyl anisole (171) was converted to bromide (172) by metalation, formylation and bromination. Alkylation with cyclopropyl ketoester produced (173) whose transformation to alcohol (174) was achieved by saponification, decarboxylation and reduction.. Its conversion to homoallylic bromide (175) was accomplished by the method of Julia et al. [56]. Alkylation of ethyl acetoacetate with bromide (175) furnished p-ketoester (176). It was subjected to cyclization with stannic chloride in dichloromethane. The resulting tricyclic alcohol provided the olefinic ester (177) by treatment with mesylchloride and triethylamine. Epoxidation followed by elimination led to the previously reported intermediate (146) whose conversion to triptolide (149) has already been described. 

In order to accomplish a total dehalogenation to hydrocarbons, dissolving metal reductions are most commonly employed. Cyclopropyl chlorides and bromides are satisfactorily reduced by alkali metal in alcohoF or in liquid ammonia. However, the fluorides are usually resistant to the hydrogenolysis. gem-Difluorides have been... 

Moreover, cyclopropyl radicals, generated by the NaBH4 reduction of cyclopropyl-mercuric bromide in the presence of excess olefins possessing one or two electron-withdrawing groups, yielded the addition product in good yields (60%) (Table 8). 

The almost negligible net retention observed in the reactions of the chloride 52-CI with LiN, NaN and KN excludes even the involvement of a cyclopropyl radical trapping reaction as being responsible for the distinct net retentions observed in the reductions of the bromide and the iodide 51-Br and 5(1-1, respectively. 

The electrochemical reduction of cyclopropyl halides has been widely investigated mainly in relation to its stereochemistry. No ring-opened products have been reported yet but substitution of the halogen by a hydrogen usually proceeds in high yields. Both monohalocyclopropanes, mostly bromide derivatives, and gem-dihalocyclopropanes were investigated. Several groups have studied the stereochemistry of the electroreduction... 

Cyclopropyl sulfones 3 are easily reduced to cyclopropanes 4 by treatment with sodium amalgam in refluxing ethanol. Yields above 80% have been reported.However, quite different reaction conditions are required to perform reductive desulfurization of cyclopropanesulfinic acids 5, i.e. the use of mercury(II) chloride, concentrated hydrochloric acid, and heat ethylmagnesium bromide followed by acid has also been used but yields were poor. ... 

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