Cyclopropane carboxylates, cycloadditions

R and R may be H, methyl, cyclopropyl, cyano, or ester groups. The phenylcarbene formed on irradiation of trans-l,2-diphenyloxirane has been trapped and identified in the form of a cyclopropane derivative in methanol in the presence of benzyl methyl ether and alkenes. Photolysis in the presence of 2,3-dimethyl-2-butene proceeds by cycloaddition with the formation of cyclopropane-carboxylic acid and oxetane derivatives (Eq. 368). ... 

An instructive example for pathway 6-37 A was found by Franck-Neumann and Miesch (1984). Reaction (6-38) demonstrates that the cycloaddition with 2-diazopropane takes place, as expected, at the double bond of methyl 5-methyl-hexa-2,4-dienoate (6.87) substituted by the (electron-withdrawing) ester group. The intermediate dihydropyrazole can be isolated. It is interesting, however, that in the subsequent azo-extrusion leading to the substituted cyclopropane carboxylate 6.88 (trivial name crysanthemic ester), the cis/trans ratios of the thermal, of the photolytic (high pressure Hg lamp), and of the benzophenone-sensitized photolytic methods are very different, in spite of the yield being the same (90%). 

Ring-Fluorinated Pyrazolines Fluorinated olefins undergo 1,3-dipolar cycloaddition reactions with diazomethane to produce fluorinated pyrazolines. In some cases, these are not isolated but are directly converted to fluorinated cyclopropanes by extrusion of nitrogen, either thermally or photochemically. For example, reaction of a series of 2-aryl-3-fluoroacrylates with diazomethane produced intermediate fluorinated pyrazolines that were ponverted to a series of 1-aryl-l-cyclopropane carboxylates by irradiation at 3500 A (Fig. 3.75). The esters in turn were... 

Ring contraction reactions of the Faworski-type have been extensively investigated to synthesize pyrethroid cyclopropane-carboxylic acids, using the smooth 2 + 2 cycloaddition of haloketenes to olefins [60] (Reaction schemes 30, 31) forming 2-halocyclobutanones 45-49, which in an alkahne medium rearrange to cyclopropane carboxyUc acids. 

Recently, cyclopropane derivatives were produced by a ruthenium-catalyzed cyclopropanation of alkenes using propargylic carboxylates as precursors of vinylcarbenoids [51] (Eq. 38). The key intermediate of this reaction is a vinylcarbene complex generated by nucleophilic attack of the carboxylate to an internal carbon of alkyne activated by the ruthenium complex. Then, a [2+1] cycloaddition between alkenes and carbenoid species affords vinylcyclo-propanes. 

Dihydro-2-isopropyl-3.6-dimethoxypyrazine, a bis(lactim)ether, is converted into the 5-di-azo compound 1 by lithiation and diazo group transfer. The intermediate diazo compound reacts at room temperature with olefins such as cyclohexene to produce the cyclopropane derivatives with excellent diastereoselectivity . The derivative from cyclohexene is hydrolyzed by acid treatment to give methyl 7-cv(cfo-aminobicyclo[4.1.0]hcptane-7-carboxylate. The bis(lac-tim)ether diazo compound 1 is also involved in an exceptional asymmetric [2 + 1J cycloaddition producing cnantiomerically pure cyclopropenc derivatives4. Thus, reactions of the diazo compound with monosubstituted alkynes afford the spiro compounds as one diastereomer. Hydrolytic removal of the auxiliary and protection of the amino group provides enantiomerically pure methyl l-amino-2-arylcyclopropene-l-carboxylates in moderate overall yield. 

Menthol [(—)-l] has been used as a chiral ligand for aluminum in Lewis acid catalyzed Diels-Alder reactions with surprising success2 (Section D.l.6.1.1.1.2.2.1). The major part of its application is as a chiral auxiliary, by the formation of esters or ethers. Esters with carboxylic acids may be formed by any convenient esterification technique. Esters with saturated carboxylic acids have been used for the formation of enolates by deprotonation and subsequent addition or alkylation reactions (Sections D.l.1.1.3.1. and D.l.5.2.3.), and with unsaturated acids as chiral dienes or dienophiles in Diels-Alder reactions (Section D. 1.6.1.1.1.), as chiral dipolarophiles in 1,3-dipolar cycloadditions (Section D.l.6.1.2.1.), as chiral partners in /(-lactam formation by [2 + 2] cycloaddition with chlorosulfonyl isocyanate (SectionD.l.6.1.3.), as sources for chiral alkenes in cyclopropanations (Section D.l.6.1.5.). and in the synthesis of chiral allenes (Section B.I.). Several esters have also been prepared by indirect techniques, e.g.,... 

General Methods.— The cyclopropanation of alkenes with diazocarbonyl compounds is one of the most widely used procedures for the synthesis of functionalized cyclopropanes. This year has seen the introduction of molybdenum hexacarbonyl/ palladium(ii) carboxylate, and iodorhodium(lll) mesotetraphenylporphrin as useful catalysts for this method of cyclopropanation. Reactions between diazomethane and alkenes often lead to pyrazolines [e.g, (1)] by 1,3-dipolar cycloaddition. Whereas thermolyses of these pyrazolines lead mostly to olefinic products [e.g, (3)], Martelli and Gree have now shown that Ce ions in acetone at 0 °C catalyses their decomposition to give largely cyclopropanes [e.g. (2)]. ... 

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