Cyclopropane cyclopropyl bromide

Cyclophanes, 24 37-38 Cyclopropanes, 13 654 26 654 Cyclopropenyl acids, 5 28 Cyclopropylamine (CPA) in nevirapine synthesis, 15 741-742 physical properties of, 2 498t Cyclopropyl bromide, physical properties of, 4 350t... 

Since the carbon-carbon bonds in strained cyclopropane rings have large s-character, cyclopropyl bromides underwent smooth bromine-magnesium exchange by the action of lithium tributylmagnesate (equation 27)". 

Among transition metal complexes, the ubiquitous dicarbonylcyclopentadienyliron (Fp) complexes are the first, and perhaps the best, representatives to demonstrate the utility of metal-halogen exchange reactions in metallacyclopropane synthesis. Thus, reaction of the readily available sodium dicarbonylcyclopentadienyliron [Cp(CO)2Fe]Na (FpNa) with the parent cyclopropyl bromide " and derivatives " gave in moderate yields the corresponding cyclopropane-Fp complexes (equation 3). 

The reaction of hot bromine atom with cyclopropane and cyclopropyl bromide... 

This step cannot be followed up since it does not lead to radioactive organic products. However, the fact that the sum of CH2=CHCH Br and CHf Br is almost independent of the pressure indicates that this last step is of small imprortance in the case of Br + cyclopropane. This step, however, is important in the case of Br-I-cyclopropyl bromide. For Br -f cyclopropyl bromide Saeki and Tachikawa found that the increase of total pressure led also to a decrease in the yield of tHf Br and increase in the yield of CH2 =CHCH Br. However, while the yield of CH Br decreased from 3.1 % to 2.1 % (when the pressure was changed from 1.37 to 13.4 kPa), the yield of CH2=CHCH2Br increased from 3.0 to 12.3%. The difference between the decomposition of c-CaHf Br formed by either Br for H reaction or Br for Br reaction was explained by Saeki and Tachikawa as due to the higher energy (above 4 eV) left in the molecule in the Br-for-H reaction which... 

The effect of the electron scavenger, CS2, is explained as due to preventing the neutralization of the cations in the system and subsequent reaction of in the state with cyclopropane or with the radiolytic products of the substrate. In the presence of CS2 the major product is methyl iodide similarly to the major product of Br found by De Jong and coworkers . However the analog to the main product in the case of I2 or O2 as scavenger, namely, n-propyl bromide was not found at all by De Jong and co workers. They found the second and third major products to be allyl bromide and cyclopropyl bromide while Certout and Schleifer did not find the respective iodides at all. It is not clear if this is due to the difference between Br and I or due to the different amount of radiolysis induced by each of them. 

The most general entry into functionalized sulfur-containing cyclopropanes is the addition reactions of cyclopropanones and thiols (see Section 5.2.3.5.4.). Thus, reaction of cyclo-propanone with thiols in dichloromethane affords l-(alkylsulfanyl)cyclopropanols 39 which are readily transformed into the corresponding cyclopropyl bromides 40 and cyclopropyl chlorides 41 upon reaction with anhydrous hydrogen bromide and hydrogen chloride, respectively. ... 

Cyclopropanation, 40, 172 Cyclopropanes, 420-421,453-454 Cyclopropanone dithioketals, 306 Cyclopropenation, 434-435 Cyclopropylacetic acid, 377 Cyclopropyl alcohols, 445 Cyclopropyl bromides, 291 Cyclopropylidenetriphenylphosphoiane, 339... 

Whereas photosensitized bromination of cyclopropane affords 1,3-dibromo-propane, bromination with NBS gives cyclopropyl bromide. Thus, whereas Br reacts exclusively by attack on carbon to give ring-opening, the succinimidyl radical abstracts hydrogen to give a cycloprop radical, which rapidly combines with a bromine atom. ... 

The Hunsdiecker process has the disadvantage of requiring dry silver salts. As a consequence, other methods have been sought, and it has been found that some carboxyhc acids undergo oxidative decarboxylation on formation of mercury (Hg), lead (Pb), or copper (Cu) salts. For example, cyclopropane carboxyhc acid, on treatment with bromine (Br2) in the presence of red mercury(II) oxide (HgO), yields hydrogen bromide (HBr), carbon dioxide (CO2), and bromcxyclopropane (cyclopropyl bromide) as shown in Equation 9.84. 

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... 

Not surprisingly, the enthalpy of reaction for cyclopropyhnagnesium bromide, —282.8 kJmol , is somewhat of an outlier, given the numerous anomalies associated with this small ring . For example, cyclopropane is the most olefinic and most acidic of the cycloalkanes—which correctly suggests that cyclopropyl forms the most polar C—Mg bond and, accordingly, is the thermodynamically most stable cycloalkylmagnesium species. 

Alternatively, the reaction of cyclopropylethynylmagnesium bromide with cyclo-propanone hemiacetal gives l-(cyclopropylethynyl)cyclopropanol (equation 152)232. The reaction of cyclopropanone acetal with other alkynyl Grignard reagents serves as a general route to alkynylcyclopropanols. Similarly, alkynyllithium derivatives of vitamin D were coupled with cyclopropane carbonyl isoxazolidine to give the corresponding alkynyl-cyclopropyl ketones (equation 153). 

Cyclopropyl sulfones 3 are easily reduced to cyclopropanes 4 by treatment with sodium amalgam in refluxing ethanol. Yields above 80% have been reported.However, quite different reaction conditions are required to perform reductive desulfurization of cyclopropanesulfinic acids 5, i.e. the use of mercury(II) chloride, concentrated hydrochloric acid, and heat ethylmagnesium bromide followed by acid has also been used but yields were poor. ... 

Conversion of (Cyclopropyl)triphenylphosphonium Bromides to Cyclopropanes General Procedure ... 

The a proton of a substituted cyclopropane is also rendered acidic if the substituent is attached to the ring by C-P bonds. A few reports have appeared on a-substitution in such compounds.(Cyclopropyl)triphenylphosphonium bromide was converted to a (1-ethoxy-carbonylcyclopropyl)triphenylphosphonium salt 18 in 80% yield by sequential treatment with lithium diisopropylamide and ethyl chloroformate. Furthermore, some diethyl cyclopropyl-phosphonates were converted, in some cases in excellent yield, to diethyl (1-hydroxymethyl-cyclopropyl)phosphonates by treatment with lithium diisopropylamide followed by addition of an aldehyde." Thus, typically, diethyl 2-hexylcyclopropylphosphonate gave diethyl 2-hexyl-l-[hydroxy(phenyl)methyl] cyclopropylphosphonate (19b) in 90% yield on reaction with benzaldehyde. ° Other electrophiles such as acetone, acetyl chloride, acetic anhydride, and ethyl acetate, were not sufficiently reactive to undergo addition to the anion. 

Substitution of a halomercury group attached to a cyclopropane has also been carried out via a cyclopropyl anion. When cii-2-(diisopropylaminocarbonyl)-2-methylcyclopropyltnercury chloride (2) was treated sequentially with an excess of methyllithium or methylmagnesium bromide and then with carbon dioxide, acidic aqueous workup gave, in very good yield, cis-2-(diisopropylaminocarbonyl)-2-methylcyclopropanecarboxylic acid (3a, 74% from 2), which was esterified with diazomethane to give methyl cw-2-(diisopropylaminocarbonyl)-2-methyl-cyclopropanecarboxylate (3b, 90% from 2 when 3a was not isolated). ... 

Acetyl methansulfonate proved to be very efficient in opening the cyclopropane ring in cyclopropyl ketones with simultaneous attack by a nucleophile such as bromide, iodide, or methanesulfonate to yield substituted enol acetates. This reaction was successfully applied to polycyclic systems. ... 

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