Benzyl alcohol bromide

J.M.J. Frechet (C. J. Hawker, 1990) replaced the divergent synthesis by a convergent growth of a dendritic polymer. The repeatedly employed monomer, 5-hydroxymethyl-l, 3-benzenediol, was 1,3-O-dibenzylatcd with 3,5-bis(benzyloxy)benzyl bromide. The resulting benzyl alcohol containing 7 benzene rings was converted to the benzyl bromide which was... 

HBr, AcOH, reflux, 30 min, 85%. The efficiency of this method is significantly improved if a phase transfer catalyst ( -Ci6H33P Bu3 Br ) is added to the mixture. Methods that use HBr for ether cleavage can give bromides in the presence of benzylic alcohols. ... 

In 1983, Nozaki, Takai, Hiyama, and their coworkers disclosed that vinyl and aryl iodides or bromides are reduced with chromium(n) chloride, and that the resulting organochromium(in) species react smoothly with a host of aldehydes to give allylic or benzylic alcohols in excellent yields.6 As shown in Scheme 1, the chromium(n) chloride-mediated carbonyl addition can be conducted efficiently at... 

Benzyl alcohol, a-vinyl- [Benzene-methanol, a-ethenyl-), 106 Bcnzylamine-polystyrene [Benzene, di-ethenyl-, polymer with ethenyl-benzene, aminomethylated), 95 Benzyl bromide [Benzene, (bromo-methyl)-, 78... 

The common microwave oven has been brought into the laboratory. Using special Teflon reaction vessels, components are mixed together, the vessel sealed and put into the microwave oven. Reaction times are greatly accelerated in many reactions, and reactions that took hours to be complete in refluxing solvents are done in minutes. Benzyl alcohol was converted to benzyl bromide, for example, using microwaves (650 W) in only 9 min on a doped Montmorillonite K-10 clay. This is a growing and very useful technique. 

DMSO or other sulfoxides react with trimethylchlorosilanes (TCS) 14 or trimefhylsilyl bromide 16, via 789, to give the Sila-Pummerer product 1275. Rearrangement of 789 and further reaction with TCS 14 affords, with elimination of HMDSO 7 and via 1276 and 1277, methanesulfenyl chloride 1278, which is also accessible by chlorination of dimethyldisulfide, by treatment of DMSO with Me2SiCl2 48, with formation of silicon oil 56, or by reaction of DMSO with oxalyl chloride, whereupon CO and CO2 is evolved (cf also Section 8.2.2). On heating equimolar amounts of primary or secondary alcohols with DMSO and TCS 14 in benzene, formaldehyde acetals are formed in 76-96% yield [67]. Thus reaction of -butanol with DMSO and TCS 14 gives, via intermediate 1275 and the mixed acetal 1279, formaldehyde di-n-butyl acetal 1280 in 81% yield and methyl mercaptan (Scheme 8.26). Most importantly, use of DMSO-Dg furnishes acetals in which the 0,0 -methylene group is deuter-ated. Benzyl alcohol, however, affords, under these reaction conditions, 93% diben-zyl ether 1817 and no acetal [67]. 

In one accident, benzyl bromide had been stored on zeolites. The bottle detonated after eight days because of the overpressure resulting from the formation of large quantities of hydrogen bromide. This accident was put down to the Friedel-Crafts reaction (see on p.256) of benzyl bromide, itself catalysed by zeolites. This is an identical behaviour to the one described with benzyl alcohol on p.256. 

The low yields, which are observed among styrenyl adducts, reflect a combination of the poor reactivity of the styrene at the low temperature of the reaction. For example, the combination of t-butyl Grignard with the 2,4-bis-OBoc-benzyl alcohol 15 affords the corresponding benzopyran 50 in only 50% yield even when carried out in the presence of 5-10 equivalents of the styrene (method H, Fig. 4.27).27 Yields for substituted benzopyran styrene adducts are still lower (method G, Fig. 4.27). For example, addition of methyl lithium to 2,4-bis-OBoc-benzylaldehyde 5 followed by the addition of the dienophile and magnesium bromide affords benzopyran 51 in a paltry 27% yield. Method F is entirely ineffective in these cases, because the methyl Grignard reagent competes with the enol ether and with styrene 1,4-addition of methyl supercedes cycloaddition. 

As expected, other enol ethers work well in these procedures. For example, Jones and Selenski find that implementation of method F, which occurs by addition of MeMgBr to benzaldehyde 5 in the presence of dihydropyran (DHP) at 78 °C affords a 66% yield of the corresponding tricyclic ketal 59 with better than 50 1 endo diastereoselectivity (Fig. 4.31).27 On the contrary, Lindsey reports use of method H with the benzyl alcohol 35 and diethylketene acetal. The cycloaddition reaction occurs almost instantaneously upon deprotonation of the benzyl alcohol 35 by f-butyl-magnesium bromide in the presence of the ketene acetal and yields the corresponding benzopyran ortho ester 60 in a 67% yield.29... 

The above section already introduced the influence of leaving groups at the benzylic position that eliminate to form and regenerate QM3, and the trend extends beyond adducts formed by the deoxynucleosides as expected. The standard benzylic acetate of QMP4 eliminates completely from the deprotected phenol under neutral aqueous conditions and ambient temperature within approximately 20 h, while an equivalent benzyl bromide eliminates completely within 5 min.48 Benzylic phosphates are also extremely labile, and, if the phosphate backbone of DNA is able to trap QM, the resulting products are likely to be too labile for standard detection.53,54 In contrast, amines and thiols are much less susceptible to elimination from the benzylic position and require forcing conditions to regenerate the parent QM.26,30 The benzylic alcohol derivative also appears stable under almost all thermal conditions and only eliminates routinely to form a QM after photochemical excitation.55... 

See Benzyl chloride Catalytic impurities Benzyl alcohol Hydrogen bromide, Iron... 

Benzyl alcohol Hydrogen bromide, Iron l,2-Bis(chloromethyl)benzene Catalytic impurities See other gas evolution incidents, polycondensation reaction incidents... 

Benzyl alcohol contaminated with 1.4% of hydrogen bromide and 1.1% of dissolved iron(II) polymerises exothermally above 100°C. Bases inhibit the polymerisation reaction. In a laboratory test, alcohol containing 1% of HBr and 0.04% of Fe polymerised at about 150° with an exotherm to 240° C. Formation and iron-catalysed poly-condensation of benzyl bromide seems to have been implicated. See Benzyl bromide Molecular sieve, or Catalytic impurities See Other BENZYL COMPOUNDS, POLYCONDENSATION REACTION INCIDENTS... 

Acetyl-3-methyl-4,5-dihydrothiophen-4-one Benzyl alcohol, Hydrogen bromide, Iron Benzyl bromide, Molecular sieve Benzyl chloride, Catalytic impurities Benzyl fluoride l,2-Bis(chloromethyl)benzene Ethylene oxide, Contaminants Furoyl chloride... 

Benzene bromide, see Bromobenzene Benzene carbinol, see Benzyl alcohol Benzenecarboxylic acid, see Benzoic acid Benzene chloride, see Chlorobenzene Benzene-1,4-diamine, see p-Phenylenediamine... 

Figure 10. Cyclic voltammetric response at the NPyeCME for the oxidation/ reduction reaction of benzyl alcohol (32 mM)/C10 in aqueous 4.1 mol NaOCl (A) and nonaqueous CH2CI2 (B) solutions at a scan rate of 50 mV/s. (C) Cartoon for the NPyeCME. Inset (A) corresponds to an enlarged version of the oxidation part without (a) and with (b) benzyl alcohol. In order to marntam the electrical conductivity, 0.1 M tetrabutylammonium bromide (TBAB) is added into the CH2CI2 solution.

Other hydrides used for the conversion of esters to alcohols are magnesium aluminum hydride in tetrahydrofuran [89, 577] and magnesium bromohydride prepared by decomposition of ethylmagnesium bromide at 235° for 2.5 hours at 0.5mm [7055]. They do not offer special advantages (the latter giving only 35% yield of benzyl alcohols from ethyl benzoate). 

The construction of the oiganometallic dendron required two synthetic transformations. Selective alkylations of the phenolic hydroxyl groups in the presence of potassium carbonate and I8-crown-6 afforded the ether dimetallic derivative 35. This first generation benzyl alcohol 35 was converted to the benzyl bromide 36 by... 

The reaction of o-nitrobenzaldehydes with some benzene derivatives in the presence of strong acid (H2S04, PPA) is a classical synthesis of acridinol N-oxides (373) (37BSF240) The synthesis works for benzyl alcohol, benzene, toluene and halobenzenes, but not for benzoic acid, benzonitrile, dimethylaniline, or nitrobenzene. Isoquinoline N-oxides (374) have been obtained from o-bromobenzaldoxime or the acetophenone derivative, and active methylene compounds with copper bromide and sodium hydride (77S760). The azobenzene cobalt tricarbonyl (375) reacts with hexafluorobut-2-yne to give a quinol-2-one (72CC1228), and the 3,4,5-tricyanopyridine (376) is formed when tetracyanoethylene reacts with an enaminonitrile (80S471). 

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