SUBSTITUTED CYCLOPROPANES

Transition metals 172 a-bonded to cyclopropanes, substituted on the a-carbon with a halogen atom, are interesting intermediates for cyclopropylidene complexes 173 or allene ones 174 [88]. The former complexes are also supposed to be precursors of the above-mentioned nickel enolates. (Scheme 65)... 

Bromo- and iodocyclopropanes cannot be prepared by the direct halogenation of cyclopropanes. Substituted chloro- and bromocyclopropanes have been synthesized by the photochemical decomposition of a-halodiazomethanes in the presence of olefins iodocyclopropanes have been prepared from the reaction of an olefin, iodoform and potassium f-butoxide followed by the reduction of diiodocyclopropane formed with tri-w-butyl tin hydride. The method described employs a readily available light source and common laboratory equipment, and is relatively safe to carry out. The method is adaptable for the preparation of bromo- and chlorocyclopropanes as well by using bromodiiodomethane or chlorodiiodomethane instead of iodoform. If the olefin used will give two isomeric halocyclopropanes, the isomers are usually separable by chromatography. ... 

A primary alcohol and amines can be used as an aldehyde precursor, because it can be oxidized by transfer hydrogenation. For example, the reaction of benzyl alcohol with excess olefin afforded the corresponding ketone in good yield in the presence of Rh complex and 2-amino-4-picoline [18]. Similarly, primary amines, which were transformed into imines by dehydrogenation, were also employed as a substrate instead of aldehydes [19]. Although various terminal olefins, alkynes [20], and even dienes [21] have been commonly used as a reaction partner in hydroiminoacylation reactions, internal olefins were ineffective. Recently, methyl sulfide-substituted aldehydes were successfully applied to the intermolecu-lar hydroacylation reaction [22], Also in the intramolecular hydroacylation, extension of substrates such as cyclopropane-substituted 4-enal [23], 4-alkynal [24], and 4,6-dienal [25] has been developed (Table 1). 

Conjugate addition to cyclopropanes.1 In the presence of C2H5A1C12, allyltrimethylsilane undergoes conjugate addition to cyclopropanes substituted by gem-alkoxycarbonyl groups. 

Cyclopropyl carbanions. Attempts to deprotonate cyclopropanes substituted by a electronegative group result in dimerization or trimerization. The desired carbanions can be generated in situ by desilylation of an a-(trimethylsilyl)cyclopropane derivative with BU4NF or C(,H,CH,N(CH,),F and used to effect aldol condensations. 

It was suggested that the failure to detect stabilization due to conjugative interactions in substituted cyclopropanes may arise from other destabilizing interactions such as unfavorable electronic interactions or steric effects. Thus even though conjugation could favor certain structures, other unfavorable interactions in cyclopropanes substituted with electronegative groups could result in a situation where there was no net stabilization. 

Proton removal from mixed cyclopropylisopropylphosphonium salts to form phos-phoranes gave only the products 182 resulting from proton removal from the isopropyl groupsHowever, sulfur ylids such as 183 may be prepared and have found wide application in synthesis Equilibrium acidities of cyclopropanes substituted with a variety of sulfonyl-type substituents have also been measured ... 

The chemistry of cyclopropanes substituted with C(0)R groups goes back to the turn of the century. Kohler and his group studied the reaction of the cyclopropane 195 with sodium methoxide which eventually leads to the formation of 197. 

Cyclopropanes Substituted with Phenyl(Aryl) Groups... 

The reaction of selenium ylides stabilized by a carbonyl function with a,jS-unsaturated ketones afforded cyclopropanes substituted with two ketone functions, e. g. formation of 19 ° (see also refs 161 and 162). 

In most cases, treatment of allylic halides containing one ASG with a nucleophile does not result in formation of electrophilic cyclopropanes (MIRC product) instead, other reaction pathways are followed, e.g. addition, substitution, rearrangement and elimination reactions.However, with certain alkenes or nucleophiles or under the appropriate conditions a conjugate addition-nucleophilic substitution pathway is favored, resulting in cyclopropanes substituted with one ASG. Representative examples are compiled in Tables 20 and 21 where organometallic compounds or active methylene compounds are used as the nucleophilic species in combination with allyl bromides containing an ester or a sulfone as ASG. 

Cyclopropanes substituted with four or less functional groups were synthesized in reasonable yield using -vinylsulfoximine derivatives and mono- or di-activated (Table 27) or even nonac-tivated (Table 28) carbon nucleophiles. 

During the preparation of l-chloro-l-(2-furyl)cyclopropanes a small amount (up to 12%) of 5-tert-butoxy-2-chloromethylene-2,5-dihydrofuran, the addition product of potassium tert-butoxide to the bipolar structure of chloro(2-furyl)carbene, was formed.Cyclopropanes substituted at C 3 in the thiophene ring are sometimes unstable to column chromatography. The sterically more crowded chloro(3-phenyl-2-thienyl)carbene failed to undergo addition to 2,3-dimethylbut-2-ene. ... 

Cyclopropane (and its derivatives) can undergo thermally induced ring opening to a 1,3-diradical with subsequent H-shift to propene. Stereochemical, kinetic and mechanistic aspects of this reaction for cyclopropane, substituted cyclopropanes and cyclopropane-containing polycyclic structures have been exhaustively reviewed. ... 

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