Derivatives of Alcohols and Phenols

It is only with sufficiently sterically bulky ligands, such as 2,6-di-tertbutyl-4-methylphenolate (BHT), that monomeric A1 species are formed Me2Al(BHT) and MeAl(BHT)2 (12 and 13, Fig. 6) [106, 107]. The isolation of these monomeric compounds is undoubtedly attributable to the steric hindrance of the aryloxide precluding dimerization via bridging by the aryloxide moieties. For these compounds, the short Al-O distances and large Al-O-C bond angles observed in the solid state were proposed to arise from n-interaction between the vacant p orbital on aluminum and the lone pairs on the aryloxide oxygens (structure 14, Fig. 6). 

Although such a bonding scheme is compatible with the commonly accepted concept (i.e., the presence of any form of ft-bonding to a group 13 element would require a trigonal planar coordinatively xmsaturated metal center), the relative importance of jt-donation from the aryloxide to aluminum in this group of compounds has not achieved a consensus [106-109]. 

Despite steric hindrance, all monomeric aryloxide compounds reported to date have readily formed Lewis acid-base complexes, in which the aluminum is four-coordinate [106, 109, 110]. For their intrinsic attractive features, sterically hindered three-coordinate aluminum aryloxides have been developed and subsequently used as Lewis acid catalysts for stereo-, regio-, and chemo-selective carbon-carbon bond-forming reactions [111]. Compared with classical Lewis acids, these aluminum reagents coordinate strongly with various oxygen-containing substrates, and this coordination is affected by the steric environment of then-ligands. 

Undoubtedly, further studies will stimulate chemists to develop new ligand t)q)es, and thus to advance both fundamental and applied directions for this field of bifunctional catalysts. 

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We have found that this sequence can be generally applied to the synthesis of hydroxypropyl derivatives of alcohols and phenols yields are uniformly acceptable and products of the desired degree of chain extension can be prepared completely free of lower and higher oligomers. The compounds shown in Table I were prepared using this chemistry. 

See also page 47, Section 93 and page 49, Section 9.4, for reduction of sulfur-containing derivatives of alcohols and phenols and page 229, Section 4, for reduction of allylic sulfonates and sulfones with double bond transposition. 

Formates have been prepared by the reaction of chloromethyleneiminium salts with derivatives of alcohols and phenols. Yields are generally good. ... 

Among the reactions appended to this preparation, the foi-mation of phenylcaibiniide from phenyl mustard oil is desciibetl. It should be noted that phenyl carbimide, like the thiocarbiniide, unites with ammonia, amines, and more especially with alcohols and phenols. The bases yield urea derivatives the alcohols and phenols foim urethanes. 

Further examples of the reaction ROH -> RC02R are included in Section 107 (Esters from Acid Derivatives) and in Section 45 A (Protection of Alcohols and Phenols). 

REDUCTION OF ALCOHOLS AND PHENOLS AND THEIR SUBSTITUTION DERIVATIVES... 

After the sulfation of alcohols and phenols was reported to proceed efficiently with DCC/ H2S04, 75 76 Wieland et al. 81 applied this procedure for the sulfation of the tyrosine residue in D-Tyr6-a//-D-retro-antamanide. This contains no reactive group in addition to the phenolic group, and the desired product was obtained in satisfactory yields. Despite these promising initial results, this type of sulfation reaction has been adopted only sporadically, e.g. for sulfation of the CCK-8 derivative Boc-Asp(OtBu)-Tyr-Met-Gly-Trp(For)-Met-Asp-(OtBu)-Phe-NH2 with 70% yield1 2 or for the preparation of an intermediate fragment in the synthesis of CCK-related peptides (Scheme 3). 83 ... 

Selective oxidation of alkanes and benzene derivatives to alcohols and phenols, respectively, are among the most difficult reactions in oxidation catalysis. Therefore, the stoichiometric hydroxylation of alkenes and aromatics performed by a-oxygen at room temperature has aroused great interest as a potential way for developing new steady state catalytic processes for the preparation of these valuable products, similar to the hydroxylation of benzene to phenol. 

The study of structural differences of alcohols and phenols [8], using as a characteristic the ratio of the adjusted retention time of the alcohol or the phenol to that of its TMS derivative, can serve as an example of the first aspect. Alcohols, thiols and primary and secondary amines in food flavours were identified successfully after the preparation and GC analysis of different derivatives [9]. The third method is fairly frequent in the analysis of residues of pesticides (see p.177). 

III. Condensation of Alcohols and Phenols with Sugars and Sugar Derivatives.. 163... 

Parameters such as solvent, basic medium and reaction time, affecting the derivatization of alcohols and phenols with benzoyl chloride, were investigated. End analysis was by GC with UVD . a sensitive method proposed for trace determination of phenols in water consists of preconcentration by SPE with a commercial styrene-divinylbenzene copolymer, acylation with pentafluorobenzoyl chloride in the presence of tetrabutylammonium bromide and end analysis by GC with either ECD or ITD-MS. LOD was 3 to 20 ngL for ECD and 10 to 60 ngL for ITD-MS, with 500 mL samples . Acylation with the fluorinated glutaric acid derivative 43 was proposed for determination of urinary phenols, as indicative of exposure to benzene and other aromatic hydrocarbons. End analysis by GC-MS shows strong molecular ions of the derivatives by electron ionization. The proto-nated ions are the base peaks obtained by chemical ionization. LOD was 0.5 mgL and the linearity range 0-100 mg L for phenol . 

Dihydropyran, polystyrene supported AICI3, CH2CI2, rt, 89-97% yield. Considerable selectivity can be achieved by this method. The more electron rich alcohols react in preference to electron poor derivatives, primary alcohols react faster than 2" alcohols, alkanols react in preference to phenols and diols can be monoprotected efficiently. The catalyst A1C13-6H20 under solvent-free conditions gives THP ethers of alcohols and phenols in 74-96% yield. ... 

The Wang resin can also be used for anchoring of alcohols and phenols as ethers under Mitsunobu conditions [202,203] the ethers, unlike ethers derived from the Merrifield resin, can readily be cleaved using TFA-CH2CI2 (1 1). Treatment with TFA-THF (1 2) enabled selective cleavage of an enol ether with the phenol remaining anchored to the support. Alcohols and phenols can also be anchored as ethers by reaction with the trichloroacetimidate derivatives of Wang 5e and a related PEG resin [204,205] with products cleaved under similar conditions. 

In true sense, the acetylation of alcohols and phenols is really regarded as a specific instance of esterification by virtue of the fact that the resulting acetyl derivative... 

Since the lower phenols are volatile, they are best separated after conversion into involatile, coloured derivatives (azo dyes) (see p. 664) [37, 87, 154]. The TLC of the azo compounds derived from other simple alkyl phenols also has been described in these articles [37, 87]. Eaesel-guhr layers, impregnated with formamide, have been used as well as strongly alkaline silica gel layers. After separation, the coloured derivatives can be quantitatively eluted from the layer and determined [154]. Mixtures of alcohols and phenols can be satisfactorily chromatographed as their dinitrobenzoates [38]. Numerous phenolcarboxylic acids have been separated on mixed layers of silica gel G and cellulose, using the solvents toluene-ethyl formate-formic acid (50 + 40 + 10) and chloroform-acetic acid-water (80 + 20 + 20). Phenolcarboxylic acids differing little in polarity, can be better separated if the layers are saturated with moisture before use [158]. 

Another new reagent for the protection of alcohols and phenols is 2-trimethyl-silylethoxymethyl chloride (67), said to be readily available. The derived SEM ethers (Scheme 30) are stable to acidic conditions that remove 2-tetrahy-dropyranyl, 2-tetrahydrofurfuryl, and trialkylsilyl groups, but can be cleaved by fluoride ion. Phenylthiomethyl ethers may be used in the protection of phenols. They have been reported as more resistant to hydrolysis than aliphatic or aromatic methylthiomethyl ethers, and are removed with mercuric chloride. 

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