Cyclopropanation chromium chloride

Perfluoroalkyl)methyl-substituted electrophilic cyclopropanes are synthesized in excellent yields by a chromium (III) chloride/iron powder-promoted reaction of perfluoroalkyl iodides with allylamalonic ester and its analogues (equation 51)67. Oxidative coupling of... 

Cyclopropanation reactions of nonheteroatom-stabilized carbenes have also been developed. The most versatile are the cationic iron carbenes that cyclopropanate alkenes with high stereospecificity under very mild reaction conditions. The cyclopropanation reagents are available from a number of iron complexes, for example, (9-alkylation of cyclopentadienyl dicarbonyliron alkyl or acyl complexes using Meerwein salts affords cationic Fischer carbenes. Cationic iron carbene intermediates can also be prepared by reaction of CpFe(CO)2 with aldehydes followed by treatment with TMS-chloride. Chiral intermolecular cyclopropanation using a chiral iron carbene having a complexed chromium tricarbonyl unit is observed (Scheme 61). 

Chromium(II) chloride reduction of 9a-bromo-A -3-oxosteroids 19 leads to 5,9-cyclosteroids 20. The formation of these eyclosteroids is explained by assuming a one-electron transfer in the cleavage of the C-Hal bond with chromium(II) chloride to give a carbon radical, followed by a second one-electron transfer from Cr to give a carbanionic intermediate that intra-molecularly undergoes addition to the enone moiety and thus forms the cyclopropane ring. 

For other 6-substituted derivatives, the proportions of the two products were reversed when zinc(II) chloride in methanol, or chromium(II) sulfate in aqueous dimethylformamide, was used as reductant. Lithium/ammonia reduction of ethyl 5-oxotetracyclo[5.4.0.0 . 0 ]un-dec-lO-ene-8-carboxylate (30) gave a higher proportion of the sinularene-type product, ethyl 2-methyl-4-oxotricyclo[4.4.0.0 ]decane-7-carboxylate (31), than the longifolene-type, ethyl 5-oxotricyclo[5.4.0.0 ]undecane-8-carboxylate (32). Once again, these proportions were reversed for other 8-substituted substrates when zinc metal/zinc(II) chloride in methanol, or chromium(II) sulfate in aqueous dimethylformamide, was used to induce cyclopropane cleavage. ... 

In the system at hand, diosgenin (7-2) is first converted to its 3-toluenesulfonate 10-1 by reaction with /i-toluenesulfonyl chloride (Scheme 2.10). Solvolysis of this compound under weakly acidic conditions leads to displacement of the excellent leaving group / -toluenesulfonate and formation of the cyclopropane-containing derivative 10-2. The newly formed hydroxyl group is next oxidized with chromium trioxide to give the 6-ketone... 

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