Alcohols aralkyl

Boron trifluoride etherate (in HOAc, 60-80°, 15 min, high yields) also catalyzes formation of 5-diphenylmethyl and 5-triphenylmethyl thioethers from aralkyl alcohols. 

The aralkyl alcohols and more highly substituted aliphatic alcohols (Fig. 10.2) are used mostly as preservatives. These include ... 

In the author s laboratories the polymerization of aldehydes, ketones, and alcohols by liquid hydrogen fluoride has been repeatedly noted. Acetaldehyde polymerizes and acetone forms polymeric substances on standing for a period of time in solution in hydrogen fluoride. If the solution is separated shortly after mixing, the acetone may be recovered. The same is true of tertiary alcohols. The peculiar action of tertiary chlorides (Simons et al., 35) probably results at least in part from polymerization. The products obtained most likely come from destruction of the polymers in the process of distillation. Benzaldehyde forms a shellac like resin when treated with hydrogen fluoride. A rather interesting polymerization reaction occurs upon treating aralkyl ketones with... 

Systematic investigations into this reaction have been undertaken and showed that for straight-chain aralkyl hydroperoxides and their cyclic analogues the (R)-alcohol forms, whereas the stereoselection is the opposite for branched hydroperoxides. The reaction could be applied to functionalized hydroperoxides such as a- and (3-hydroperoxy esters or hydroperoxy alcohols with good to excellent diastereo- and enantioselectivities. Up to 99% ees were obtained for small, sterically non-hindered substrates, whereas for tertiary hydroperoxides and for substrates with substituents at the co-position neither good ees nor useful turnover numbers have been reported. HRP reacts very sluggishly also with sterically demanding silyl-substituted allyl hydroperoxides. 

The N-alkylation of nitriles with aralkyl alcohols, a special case of the Ritter reaction, is a novel general reaction. The following compounds were prepared by this procedure in the corresponding yields N-benzylacetamide (48%), N-(2,4-di-methylbenzyl)-acctamide (40%), N-(4-methoxybenzyI)-acetam-ide (60%), N,N -diacrylyl-/> Xylene-a-o -diamine (64%), N,N -diacetyl-4,6-dimethyl-jM-xyleue-a, -diamine (62%). 

The rearrangement products derived from aromatic and non-aromatic heterocyclic amines crystallize readily from the lower alcohols. Unlike those of many of the A-substituted glycosylamines, the crystals are not solvated. On the other hand, the ketose derivatives of aralkyl- and alkyl-amines, such as 2-phenylethylamine, ethanolamine, diethanolamine, glycine ethyl ester, and phenylalanine (see Table II), are hydrated or alcoholated, or both, and are difficult to isolate in pure crystalline form. The crystals which have been isolated were hygroscopic. Alcohols, aqueous alcohols, and water are the most commonly used solvents for crystallization. Acetone, ether, or benzene have been added to the alcoholic media in order to increase the yield of crystalline compound. The use of solvents that contain peroxides promotes decomposition of the crystals during storage. ... 

Selenium dioxide converts aryl and aralkyl allyl ethers into aldehydes and the corresponding alcohols. Allyl benzyl ether refluxed with selenium dioxide in acetic acid and dioxane for 1 h gives a 50% yield of benzyl... 

A ketone added to the aged solution is reduced effectively, but a carboxylic acid or ester is not reduced. This weak hydride donor is thus useful for the selective reduction of a keto acid to the corresponding hydroxy acid. Both intermolecular 2md intramolecular competition experiments with tetrakis-(N-dihydropyridyl)-aluminate showed that diaryl ketones are more reactive to this reagent than either dialkyl or aralkyl ketones. This relationship is the opposite of that found by H. C. Brown for reduction with sodium borohydride in isopropyl alcohol, where the order of reactivity is acetone > acetophenone > benzophenone. 

Reagents that encompass both the alcohol and the amine functional groups of a commercially available aminoalcohol are very usefirl. Ephedrine 1.61 (R = Me), pseudoephedrine 1.78, norephedrine 1.61 (R=H) and their Aralkyl and N-acyl derivatives are commonly used, [253, 290, 320-324], as are aminoalcohols 1.79. Also popular are aminoalcohols formed from the natural aminoadds (S)-alaninol... 

Synthetic alkyl and aralkyl glycosides of N-acylneuraminic acid, obtained by the method of Koenigs and Knorr,191 are split with neuraminidase, like the natural glycosides of N-acylneuraminic acid. In contrast, the /3-D anomers (70), obtained from N-acylneuraminic acid and the appropriate alcohol in the presence of hydrogen ion, are resistant to neuraminidase.191,199 200... 

Thiols from alcohols. In toluene or DME the Lawesson s reagent directly converts aralkyl and cycloalkyl alcohols to thiols. 

When the desired product is an alkyl or aralkyl hydroperoxide or peracid, careful control of metal concentration is required to minimize hydroperoxide cleavage. When the reactant is an alcohol, the hydroperoxide is the hydrogen peroxide adduct of an aldehyde or ketone, i.e. 

The outcome of a yeast-catalysed reduction of a ketone can be predicted with some confidence. For simple dialkyl or aralkyl ketones, the product obtained is almost invariably the (S)-alcohol (Figure 4.1). 

Carbonates 822, particularly asymmetrical carbonates, with at least one simple group R can be easily obtained by reaction of an alcohol R -OH with chloroformates of the type R O—CO—Cl (R = alkyl, aralkyl, aryl), most of which are commercially available and cheap products (see also Section 4.2.1 Chloroformates ). 

The fourth item in the table, phenol (hydroxybenzene), is alkylated on oxygen, forming an ether, methoxybenzene (anisol), with the powerful alkylating agent trimethyloxonium tetrafluoroborate [(CH30)3 BFt]. Other alkoxonium tetrafluo-roborates are also commercially available and can be used to the same end with phenols, enols, and alcohols, forming aryl ethers, enol ethers, and dialkyl ethers, respectively. In contrast to dialkyl, diaryl, and aralkyl ethers, which are quite inert and are often used as solvents, enol ethers are capable of acid-catalyzed hydrolysis to produce ketones (or their equivalent enol) and the alcohol from which the enol ether is formed (Scheme 8.47). 

The Amadori rearrangement also occurs for the glycosylamine derivatives of some secondary alkylamines and of primary and secondary aralkyl-amines it occurs in alcoholic solution in the presence of compounds such as ethyl malonate and acetylacetone which contain active hydrogen atoms 66), The direct reaction product from D-glucose and dibenzylamine was actually 1-dibenzylamino-l-deoxy-D-fructose (XI) 66) and not VjV-di-benzyl-D-glucosylamine (XII) as indicated earlier by Kuhn and Birkofer 76), This rearrangement was effected without benefit of acid catalysis 70) or by the use of ethyl malonate 66), The true V,i T-dibenzylglu-cosylamine (XII) could not be isolated. 

The enzyme oxinitrilase also catalyzes the addition of prussic acid to 3-phenoxy benzaldehyde 2S0 in a moderate enantioselective manner to give the unsuitable R-enantiomer of299 [640,641]. An artificial enzyme proved to be much more efRcient. The cyclic dipeptide cyclo-(R-Phe-R-His) 300 catalyzes the enantioselective HCN-addition onto aldehydes [642] (Reaction scheme 213). In the case of 3-phenoxy benzaldehyde the desired S-enantiomer 299 is created with a high optical and chemical yield [643-646] optimally in the absence of water in aprotic solvents, catalyzed by some cyanohydrine [647] or aralkyl-alcohol [618]. Rigorous exclusion of traces of basic by-products and a preceding acidic purification step [649] gives additional improvement. 

Not surprisingly, trifluoromethanesulphonic acid can be used effectively as catalyst for the Fischer glycosidation of free sugars, and phosphorus oxychloride catalyses the reaction between sugar peracetates and alcohols. For aryl, alkyl and aralkyl D-glucoside esters /9-anomers (the kinetic products) are favoured if the reactions are carried out in benzene solution, whereas the more stable o-products predominate if no solvent is used. °... 

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