Cycloalkyl bromides, reaction

Evidence for a free radical pathway in the foregoing cycloalkyl bromide reactions was secured by San Filippo and coworkers, who found that cis and iraws-4-r-butylcydohexyl bromide afford nearly identical product mixtures with MesSnLi, MesSnNa and MesSnK under a given set of conditions (Table 7)45. Of the various combinations examined, that of di-bromide and Me3SnLi appeared to be most favorable to S/v2 displacement. 

An effect of the ring-size in addition to that observed in the elimination taking place in the reduction of vicinal dibromides, has been observed for medium-sized ring compounds which carry the electro-active group either in the side-chain or directly attached to the ring. The half-wave potentials of cycloalkyl bromides can be correlated with the half-wave potentials of cyclic ketones and their derivatives (Fig. 29). The observed relation indicates that the relative effect of ring-size on the reactivity is similar in all the reaction series compared. 

The data of Friswell et al. [51] for the reactions of the cycloalkyl bromides with sodium at 520°K can be compared with the competitive method data [35, 37] for the reaction of cycloalkyl chlorides with potassium at the same temperature (see Table 4). 

The utility of SCFs for PTC was demonstrated for several model organic reactions - the nucleophilic displacement of benzyl chloride with bromide ion (26) and cyanide ion (27), which were chosen as model reversible and irreversible Sn2 reactions. The next two reactions reported were the alkylation and cycloalkylation of phenylacetonitrile (28,29). Catalyst solubility in the SCF was very limited, yet the rate of reaction increased linearly with the amount of catalyst present. Figure 5 shows data for the cyanide displacement of benzyl bromide, and the data followed pseudo-first order, irreversible kinetics. The catalyst amounts ranged from 0.06 (solubility limit) to 10% of the limiting reactant, benzyl chloride. 

The enthalpies of formation of the cycloalkylmagnesium bromides that have been determined by reaction calorimetry are listed in Table 3. As with other functionalized cycloalkanes and the cycloalkanes themselves, there is no regularity to these values with respect to carbon number as there are for their acyclic analogs because of the influence of ring strain on the enthalpies. Unfortunately, there are no enthalpies of formation for the bromocycloalkanes with which to compare these values there are, however, enthalpies of formation for liquid phase cycloalkanes. Figure 3 is a plot of the enthalpies of formation for the cycloalkyl-MgBr vs. those for cycloalkyl-H. There is a linear relationship with... 

Reduction of aryl and alkyl halides. This reaction can be conducted in generally good yield with LiAlHi by a free-radical process initiated by irradiation of di-t-butyl peroxide. The order of reactivity of aryl halides is Arl > ArBr > ArCI > ArF. Alkyl and cycloalkyl halides are reduced efficiently, but vinyl bromides are reduced in only modest yield. 

With dibromoalkanes, the diethyl l,l-cycloalkyl-l-(ethoxycarbonyl)methylphosphonates are readily obtained by two successive alkylations in fair to good yields using NaH in THF-DMSO (Scheme 8.17), ° K2CO3 in MeCN-DMSO, NaOH (50%)/benzyl tributylammonium bromide or EtONa/EtOH, EtiO. By contrast, reaction of the potassium salt of diethyl 1-(ethoxycarbonyl)methylphosphonate with 1,3-dibromopropane leads to the formation of 1,2-oxaphosphorinane, resulting from alkylation at the methylene carbon and at phosphorus. ... 

The replacement of OH on carbon adjacent to phosphorus by Br or I using allyl bromide or Mel in the presence of carbonyldiimidazole, has been reported. The electrolysis of diisopropyl (trichloromethyl)phosphonate in DMF containing the alkyl halide RX with a carbon cathode and magnesium anode affords diisopropyl (l,l-dichloroalkyl)phosphonates (132) interestingly, the corresponding diethyl esters may be reduced further. A similar reaction leading to (l-chloro-l-cycloalkyl)phosphonic diesters (133) has already been referred to. ... 

In addition, during the course of recent mechanistic studies, new methodology for the functionalization of saturated hydrocarbons based on Gif-type protocol has been invented. These reactions are of interest as mechanistic probes and also from the point of view of synthetic utility. Thus, cycloalkanes are transformed with vaiying efficiency into mono-substituted cycloalkyl derivatives (chlorides, bromides, azides, cyanides, thiocyanates, dicycloalkyl sulfides, or nitroalkanes) by conducting iron or copper catalyzed reactions in the presence of alkali metal salts (scheme). 

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