Cyclopropane, bromo

Cyclopentene-l,2-diol, 42, 51 2-Cyclopentene-1,4-dione, 42, 36 2-Cycloeentene-1-one, 42, 38 2-Cycloeentenone, 42,38 Cyclopropane, bromo-, 43, 9 Cyclopropanecarboxylic add, conversion to bromocyclopropane, 43, 9... 

Dimethoxy-(2-methyl-2-vinyl-cyclo-propyl)- 1298 CgH. Br Cyclopropane Bromo-pentamethyl- 2321... 

Alkali metal and other iodides are effective catalysts in reactions involving aUphatic chloro and bromo compounds, such as the preparation of cyclopropane from 1,3-dichloropropane andmetaUic 2inc (141). 

Bromo-l-propenyl phenyl sulfone (104) can serve as a Michael acceptor to Grignard reagents to give cyclopropyl phenyl sulfones in good yields, (equation 85)70. Cyclopropanes prepared by this method are listed in Table 8. However, with methyl, ethyl or t-butyl... 

Malonic acid, amino-, diethyl ester, HYDROCHLORIDE, 40, 24 Malonic acid, bts(hydroxymethyl)-, DIETHYL ETHER, 40, 27 Malonitrile, condensation with tetra-cyanoethylene, 41, 99 2-Mercaptopyrimidine, 43, 6S hydrochloride of, 43, 68 Mercuric oxide in preparation of bromo-cyclopropane, 43, 9 Mesityl isocyanide, 41,103 5-Methallyl-l,2,3,4,5-pentachlorocyclo-pentadiene, 43, 92 Methane, dimesityl-, 43, 57 Methanesiileinyl chloride, 40, 62 Methanesulfonic acid, solvent for making peroxybenzoic acid from benzoic acid, 43, 93... 

Easily available copper(II) tartrate has also been used for an enantioselective cyclopropanation. From 3-methoxystyrene and 4-bromo-l-diazo-2-butanone, the cyclopropanes cis/trans-204 were obtained the mainly formed frans-isomer displayed an enantiomeric excess of 46% i99>. This reaction constituted the opening step of asymmetric total syntheses of equilenin and estrone. 

An interesting variation appears when furan reacts with the allenic carbene generated by the action of potassium ter-butoxide upon l-bromo-3,3-dimethylallene. Though the yield is only 9%, one product is reasonably assigned a structure (Scheme 52) that could hardly be approached by way of a cyclopropane intermediate. The authors comment that in an allenic carbene in the singlet state two electrons will be accommodated in the sp... 

It appears that neither the lithium carbenoid pathway nor the cyclopropanation of buta-trienes are general routes to [3]radialenes. More successful is the cyclotrimerization of 1,1-dihaloalkenes via copper or nickel carbenoids, provided the substituents at the other end of the C=C double bond are not too small. Thus, tris(fluoren-9-ylidene)cyclopropane 27 was formed besides butatriene 28 from the (l-bromo-l-alkenyl)cuprate 26 generated in situ from (9-dibromomethylene)fluorene (Scheme 3)10. The cuprate complexes formed... 

The reactive substrate (0.1 mol), CHBrI2 (10.3 g, 0.03 mol) TEBA-C1 (0.4 g, 1.7 mmol) in CH,C12 (50 ml) are stirred with aqueous NaOH (50%, 60 ml) for 17 h at room temperature. The reaction mixture is worked up as described in 7.1.11 to give a mixture of cyclopropanes (-20%) in which the 1-bromo-l-iodo derivative predominates over the 1,1-dibromo derivative by a ratio of ca. 2 1. The di-iodo compound is observed in only trace amounts (when CHBr2I is used, the dibromo derivative predominates). 

Mann and Barnes [45] have discussed the mechanism of reduction of substituted and optically active 1-bromo-and 1-iodocyclopropanes, and Hazard and coworkers [46] have investigated the reduction of l-bromo-l-carboxy-2,2-diphenyl-cyclopropane. At mercury cathodes, electrolyses of 1-bromo- and 1-iodonorbornane proceed via two-electron cleavage of the carbon-halogen bond to give mainly nor-bomane, plus a small amount of bis(l-norbomyl)mercury [47]. 

Cleavage Gem-dihalides and monohalides have been dehalogenated to chiral monohalides in the presence of alkaloids [397, 398]. l,l-Diphenyl-2-bromo-2-carboxyl (bromo or methyl carboxylate) cyclopropanes are cathodically debromi-nated in the presence of alkaloid cations with enantioselectivities up to 45% ee. A mechanism is proposed whereby the alkaloid is adsorbed at the Hg cathode, which protonates face selectively the carbanion generated by 2e reduction from the bromide [399]. 

Cyclopropanation of a tandem-radical [2 + 1] cycloaddition occurs by a Ni complex-catalyzed electroreduction of 2-bromo-or 2-iodo-l,6-diene derivatives [285]. 

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. ... 

More recent reports from Cordova [155] and Wang [156] have described the cyclopropanation of a, P-unsaturated aldehydes 99 with diethyl bromomalonates 100 and 2-bromo ethyl acetoacetate catalysed by a series of diaryIprolinol derivatives. Both describe 30 as being the most efficient catalyst in many cases and optimal reaction conditions are similar. Some representative examples of this cyclopropanation are shown in Scheme 40. The transformation results in the formation of two new C-C bonds, a new quaternary carbon centre and a densely functionalised product ripe for further synthetic manipulation. Triethylamine or 2,6-lutidine are required as a stoichiometric additive in order to remove the HBr produced during the reaction sequence. The use of sodium acetate (4.0 equivalents) as an additive led to subsequent stereoselective ring opening of the cyclopropane to give a,P-unsaturated aldehydes 101. It can be envisioned that these highly functionalised materials may prove useful substrates in a variety of imin-ium ion or metal catalysed transformations. 

Some variations of the method have been used to prepare cyclopropyl and cyclobutyl halides. Simultaneous addition of bromine and 3-bromocyclobutanecarboxylic acid to the suspension of mercuric oxide gives 1,3-dibromocyclobutane in good yield.7 Similarly, cyclopropanecarboxylic acid gives bromo-cyclopropane,9 and 3-(bromomethyl)cyclobutanecarboxylic acid gives 3-(bromomethyl)cyclobutyl bromide.10 In the latter reaction, it was found desirable to remove the water from the reaction as it is formed in order to obtain high yields. Another variation is the addition of a mixture of the acid and mercuric oxide to excess bromine in bromotrichloromethane.6... 

A review of neighbouring-group effects in natural products includes steroidal examples. The 19-acetoxy-5a-bromo-6-oxo-steroids (228) fragment with base to give the 6-oxo-A -compounds (229) which are regarded as potentially useful intermediates in prostanoid synthesis.The preparation and properties of the 6-spirocyclopropane (230) have been reported. Attempts to cleave the cyclopropane symmetrically were unsuccessful although other cleavages are discussed. ... 

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