Epoxides deoxygenations, dimethyl diazomalonate

Deoxygenation of epoxides. In the presence of rhodium(II) acetate, dimethyl diazomalonate converts epoxides into the corresponding alkcnes with formation of dimethyl oxomalonate. Alkcne isomerization or cyelopropanation is not observed. Yields arc generally >80%. 

Carbenes or carbenoids have also been reported to deoxygenate epoxides. To generate these species, dimethyl diazomalonate/rhodium(II) acetate and 9-diazofluorene 44 have been employed both reagents show high stereoselectivity. For example, ciJ-2-butene oxide is converted to cir-alkene with more than 93% retention under irradiation (350 nm) using 9-diazofluorene, and functional groups, such as carbonyl, can survive using diazomalonate and rhodium(II) acetate (equation 49). 

Alkenes are converted to epoxides by oxidation with peroxy acids, and thereby they are protected with regard to certain chemical transformations. Alkaline hydrogen peroxide selectively attacks enone double bonds in the presence of other alkenes. The epoxides can be transformed back to alkenes by reduction-dehydration sequences or using triphenylphosphine, chromous salts, zinc, or sodium iodide and acetic acid. A more advantageous and fairly general method consists, however, of the treatment of epoxides with dimethyl diazomalonate in the presence of catalytic amounts of binuclear rhodium(II) car-boxylate salts. This deoxygenation proceeds under neutral conditions and without isomerization or cy-clopropanation of the liberated alkene (Scheme 97). Furthermore, epoxides can be converted to alkenes with the aid of various metal carbonyl complexes. Thus, they may be nucleophilically opened with... 

Deoxygenation of Epoxides. In the presence of catalytic rhodium(II) acetate, dimethyl diazomalonate deoxygenates epoxides under neutral conditions (eq 11). This reaction tolerates functionality such as ketones, esters, alkyl and silyl ethers and halogen substituents, although alcohols and aldehydes undergo competing insertion reactions. 

Deoxygenation of Epoxides. Rh -catalyzed deoxygenation of epoxides with dimethyl diazomalonate was shown to occur stereoselectively. This reaction feature was used for efficient inversion of double bond configuration in azacycloundecene fragment in the total s)mthesis of manzamine C (eq 32). ... 

C-H Insertion. Insertion of carbenoid species generated from dimethyl diazomalonate in the presence of Rh into activated C-H bonds proceeds in moderate yields (eq 33). Sometimes undesired insertion into the C-H bond adjacent to the heteroatom complicates the utilization of Ganem epoxide deoxygenation procedure (eq 34). ... 

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