Alkyl Bromide Links

In 2008, the same authors reported the synthesis of polyfunctionalized /V-alkyl-[S-lac tains with high stereoselectivity in an efficient manner performing the same reaction with allyl bromide and heteroarylidene N-alkyl-amines. Interestingly, by modulating the type of alkyl group linked to the nitrogen atom, it is possible to influence the reaction stereoselectivity [164]. 

Cyclization by direct reduction of alkynes linked to halides is usually ineffective. Phenyl-substituted alkynes are more easily reduced than alkyl chlorides but more difficult to reduce than alkyl bromides and iodides. Simple alkynes are more difficult to reduce than any of the halides. Consequently, direct reduction of 6-bromo-l-phenyl-1-hexyne at a potential of cleavage of the C Br bond only affords 12% yield of benzylidenecyclo-pentane, whereas the corresponding chloride gives the saturated benzylcyclopentene in 45% yield [241], or at low substrate concentrations (< 2 mM) the benzylidene cyclopentane (80%) [242]. 

The catalytic activity of cross-linked polymeric sulfoxides differing in the functionality of the polystyrene matrix (the general formula is ( -(CH20CH2) -R, whereby (P) is the polystyrene matrix cross-linked by divinylbenzene, R = H or CH3, and n = 1, 2 or 3), has been studied in nucleophilic substitution reactions between alkyl bromides (1-bromobutane and 1-bromooctane) and phenoxides, iodides, thiocyanates or cyanides of alkaline metals under the conditions of catalytic three-phase reactions in the liquid-solid-liquid system [66]. The reaction is carried out in a toluene-water medium between 70-100°C. In the systems the rate of anion transfer from the liquid phase to the organic phase decreases in the sequence PhO > J > SCN > CN . 

The tetrakis-sulphoxides (67) have been reported as a new type of PT catalyst in a solid-liquid mode, for example in 5n reactions of 1-bromo-octane. Nucleophilic substitutions of 1-bromo-octane and benzyl bromide are again the test reactions in a report on the use of the sucrose-ethylene oxide adducts (68a) as PT catalysts in both solid-liquid and liquid-liquid modes. The methacrylate ester derivative (68b) has been polymerized to a cross-linked gel that acts in a TC capacity for the same reactions. In a related approach some modified dextran anion exchangers carrying lipophilic substituents, such as the modified hydroxypropylated dextran gel shown in (69), have been synthesized and shown to catalyse displacement reactions including the alkyl bromide to iodide transformation under TC conditions. ... 

In solution aliphatic esters are acylated or alkylated at the a position by treatment with a hindered organolithium base at dry ice temperature to generate an enolate, followed by addition of a carboxylic acid chloride or an alkyl bromide. At higher temperatures the ester self-condenses rapidly during the time of enolate generation. When the ester is bound to a slightly swellable 10-20% cross-linked PS, acylations and alkylations proceed at room temperature with 73-90% yields and little or no competing self-condensation of the ester as shown in Scheme 26. Self-condensation is retarded because it requires reaction of two polymer-bound species with each other. 

Fig. 10.8 A where the R substituents are alkyl or heterocyclic radicals to give compounds such as cetyltrimethylammonium bromide (cetrimide), cetylpyridinium chloride and benzalkonium chloride. Inspection of the stmctures of these compounds (Fig. 10.8B) indicates the requirement for good antimicrobial activily of having a chain length in the range Cg to Cig in at least one of the R substituents. In the pyridinium compounds (Fig. 10.8C) three of the four covalent links may be satisfied by the nitrogen in a pyridine ring. Polymeric quaternary ammonium salts such as polyquatemium 1 are finding increasing use as preservatives.

B., Hebestreit, K., and Platt, U. Short-lived alkyl iodides and bromides at Mace Head, Ireland Links to biogenic sources and halogen oxide production, J. Geophys. Res.-A., 104,1679-1689,... 

The ring closure to form butenolides by palladium(O) catalysis can be combined with C,C bond linking, as shown by Ma and co-workers. If using tetrakis (triphenyl -phosphane)palladium(O), the products 272 are obtained from 268 (R1 = alkyl, R2 = H) and vinyl iodides or aryl bromides and iodides R3X [304]. The authors assume that... 

Currently available BAS include cholestyramine, colestipol and colesevelam hydrochloride (colestimide). Cholestyramine comprises a long-chain polymer of styrene with divinylbenzene trimethylbenzylammonium groups, whereas colestipol is a long-chain polymer of l-chloro-2,3-epoxypropane with diethylenetriamine. Colesevelam HCl is poly(allylamine hydrochloride) cross-linked with epichlorohydrin and alkylated with 1-bromodecane and 6-bromo-hexyl-trimethylammonium bromide. Bile-acid binding is enhanced and stabilised in the latter compound by long hydrophobic sidechains, increased density of primary amines, and quaternary amine sidechains. For this reason, colesevelam HCl exhibits increased affinity, specificity and capacity to bind bile acids compared with the other BAS. Colesevelam HCl also binds dihydroxy and trihydroxy bile acids with equal affinity, contrasting with cholestyramine and colestipol that preferentially bind dihydroxy bile acids (CDCA and deoxycholic acid). The latter BAS can lead to an imbalance towards trihydroxy bile acids and a more hydrophilic bile-acid pool. 

The most important point about the alkyl halide reactivities in triphase catalysis is that the reactions which have the highest intrinsic rates are the most likely to be limited by intraparticle diffusion. The cyanide ion reactions which showed the greatest particle size and cross-linking dependence with 1-bromooctane had half-lives of 0.5 to 2 h and with benzyl bromide had half-lives of 0.13 to 0.75 h. The reactions of 1-bromooctane and of benzyl chloride which were insensitive to particle size and cross-linking had half-lives of 14 h and 3 h respectively. Practical triphase liquid/ liquid/solid catalysis with polystyrene-bound onium ions has intraparticle diffusional limitations. 

Alkylation of 2-naphthoxide ion (Eq. (6)) occurs mainly on carbon in aqueous solvents and mainly on oxygen in aprotic solvents. The product distribution is often used as a probe of the solvent environment in heterogeneous reactions. Brown and Jenkins 54) found that 40-100 % RS spacer chain catalysts 15 and 16 gave up to 98 % O-benzylation of 2-naphthoxide ion with benzyl bromide. The shorter spacer chain catalyst 16 gave 85% O-alkylation, and a conventional benzyltrimethylammonium ion resin 2 gave about 70 % O-alkylation. Because of low activity, product distribution data were obtained with varied amounts of catalyst and were extrapolated to equimolar amounts of catalyst and substrate to obtain the catalyzed O/C product ratios. Interpretation of the data also was complicated by independent evidence that catalysts 15 adsorbed 2-naphthoxide ion, in addition to that bound by ion exchange54). Essentially the same results were obtained with catalysts 24 which lack the ester link in the spacer chain 106). 

The first attempts to use macroporous polystyrene supports for onium ion catalysts were reported in the early papers of Brown and Jenkins 54) and of Regen 89). The lightly cross-linked macroporous Rohm and Haas XE-305, 46 % RS as spacer chain catalyst 15, gave O- and C-alkyl products from 2-naphthoxide ion and benzyl bromide... 

Carpenter LJ, Sturges WT, Penkett SA, Liss PS, Alicke B, Hebestreit K, Platt U (1999) Short-Lived Alkyl Iodides and Bromides at Mace Head, Ireland Links to Biogenic Sources and Halogen Oxide Production. J Geophys Res 104 1679... 

With these anthracene-linked dimeric cinchona-PTCs, the Najera group investigated the counterion effect in asymmetric alkylation of 1 by exchanging the classical chloride or bromide anion with tetrafluoroborate (BF4 ) or hexafluorophosphate (PF6-) anions (Scheme 4.10) [17]. They anticipated that both tetrafluoroborate and hexafluorophosphate could form less-tight ionic pairs than chloride or bromide, thus allowing a more easy and rapid complexation of the chiral ammonium cation with the enolate of 1, and therefore driving to a higher enantioselectivity. However, when... 

In bromination of anilines, the ortholpara ratio is significantly increased in presence of cetyltrimethylammonium bromide (CTAB) but is not altered with a symmetrical ammonium salt (TBAB). Surprisingly, increasing steric hindrance in the ortho position by N-alkylation has resulted with higher ortho-selectivity. This phenomenon is linked to the orientation of the aniline at the surface of the micellar aggregates1017. 

Azidophenacyl)thioJuridine 5 -triphosphate (134) has been prepared by alkylation of 5-thlouridine 5 -triphosphate with 4-azidophenacyl bromide. This analogue is a substrate for E.coli RNA polymerase and once incorporated into RNA can be used to study RNA-protein or RNA-nucleic acids interactions by photo-activated cross-linking. Unlike other photoaffinity labels the cross-linking... 

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