Alkenes dimethyl diazomalonate

Deoxygenation of epoxides.1 In the presence of rhodium(II) acetate, dimethyl diazomalonate converts epoxides into the corresponding alkenes with formation of dimethyl oxomuionate. Alkene isomerization or cyclopropanation is not observed. Yields are 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... 

Upon direct irradiation of dimethyl diazomalonate in various (Z)-alkenes, the corresponding CM-disubstituted cyclopropanes are obtained with a stereoselectivity of only 90% ° conversely, a cisjtrans ratio of 10 90 is obtained when ( )-but-2-enes are cyclopropanated. The stereochemical integrity of the alkene was lost to an even greater extent when 2-diazo-l-phenylethanone" was utilized giving cyclopropanes 3. 

Catalytic cyclopropanation of alkenes with diazomalonates is sometimes carried out with copper powder, but it appears that copper(I) halide/trialkyl phosphite complexes (for a procedure see Houben-Weyl Vol. E19b, p 1113), bis(acetylacetonato)copper(II), " ° and tet-raacetatodirhodium can be employed more advantageously (Table 13, entries 7-9). For the cyclopropanation of styrene with dicyclohexyl diazomalonate, however, copper(I) triflate was the catalyst of choice, while intramolecular C —H insertion at the cyclohexyl ring took place in the presence of tetraacetatodirhodium. A detailed comparison of copper catalysts for the cyclopropanation of cyclohexene, 1-methyl- and 1,2-dimethylcyclohexene, (Z)- and ( )-hept-2-ene with dimethyl diazomalonate, including competitive reaction pathways such as allylic C-H insertion and carbene dimer formation, is available. The catalyzed interaction between diazomalonic esters and enol ethers leads to cyclopropanes in some cases (e.g. ethoxymethylenecyclohexane to dimethyl 2-ethoxyspiro[2.5]octane-l,l-dicarboxylate ) and to different products in other cases (e.g. 1-methoxycyclohexene, 2-methoxy-3,4-dihydro-2/7-pyran ). This behavior is attributed to the occurence of stabilized dipolar intermediates in these reactions. 

The rhodium- or copper-catalyzed interaction of dimethyl diazomalonate with 2-(l-al-kenyl)thiophenes yields either a dimethyl 2-(2-thienyl)cyclopropane-l,l-dicarboxylate, a thiophenium ylide, or a dimethyl [5-(l-alkenyl)-2-thienyl]malonate, depending on the substituents at the alkene bond and the heterocyele. ... 

Cyclopropanation. Decomposition of dimethyl diazomalonate by direct photolysis or by transition metal catalysis in the presence of alkenes leads to cyclopropanation (eq 1). The use of alkynes to trap the carbenoid species affords cyclopropenes (eq 2). Rhodium(II) acetate-catalyzed reaction with allenes allows ready access to methylenecyclopropanes, which form the basis for a methylenecyclopentane annulation protocol (eq 3). ... 

Alkenation. Alkenation of thiolactones can be achieved by rhodium(II) acetate-catalyzed reaction with dimethyl diazomalonate (eq 12). Recently, an efficient alternative alkenation protocol has been demonstrated to be applicable to a variety of ketones and aldehydes by reaction with tributylstibine and dimethyl diazomalonate in the presence of copperfT) bromide (eq 13). This process is proposed to occur via tributylstibonium bis(methoxycarbonyl)methylide. 

NHCbz (36) Alkenylation. Rtf -catalyzed reaction of dimethyl diazomalonate with thioketones and dithiolactones leads to the formation of sulfur ylides, which rearrange into thiiranes followed by spontaneous desulfurization to alkenes (eqs 39 and 40). ... 

Cyclopropanation. Rhodium complexes have been extensively employed for catalytic carbenoid cyclopropanation of alkenes. In the presence of [Rh2(S-TBSP)4], treatment of 2-aryl-substituted 2//-chromenes with dimethyl diazomalonate furnished the desired cyclopropanes in good yields (eq 41). The cyclopropane product with a terf-butyl ester group underwent rearrangement upon treatment with Sn(OTf)2 to from a y-lactone. OMe... 

Notably, [Rh2(esp)2] (esp = a,a,a, a -tetramethyl-l,3-benzenedipropanaote) was also found to exhibit catalytic activity in the cyclopropanation reaction of styrene-type alkenes with dimethyl diazomalonate at room temperature with very low catalyst loading (0.1 mol%) (eq 42). The corresponding cyclopropanes were formed in good yields. In this reaction, alkene is employed as the limiting reagent, which is in contrast to many related reactions that an excess (>5 equiv) of alkenes was employed. 

Transition-metal mediated carbene transfer from 205 to benzaldehyde generates carbonyl ylides 211 which are transformed into oxiranes 216 by 1,3-cyclization, into tetrahydrofurans 212, 213 or dihydrofurans 214 by [3 + 2] cycloaddition with electron-deficient alkenes or alkynes, and 1,3-dioxolanes 215 by [3 + 2] cycloaddition with excess carbonyl compound120 (equation 67). Related carbonyl ylide reactions have been performed with crotonaldehyde, acetone and cyclohexanone (equation 68). However, the ylide generated from cyclohexanone could not be trapped with dimethyl fumarate. Rather, the enol ether 217, probably formed by 1,4-proton shift in the ylide intermediate, was isolated in low yield120. In this respect, the carbene transfer reaction with 205 is not different from that with ethyl diazoacetate121, whereas a close analogy to diazomalonates is observed for the other carbonyl ylide reactions. 

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