Phenylethane-l,2-diol

The solvent-free 0-silylation reaction can also be accomplished selectively. For example, when l-methyl-l-phenylethane-l,2-diol (39) was treated with 27 at 60 °C for 5 h, its primary hydroxyl group was silylated to give 40 in 70% yield. 

The secondary benzylic alcohol l-phenylethan-l,2-diol requires 20 hours of treatment at room temperature to produce a 64% yield of 2-phenylethanol (Eq. 43).137 Under the same conditions, methyl mandelate fails to undergo reduction, presumably because of the greater carbocation-destabilizing effect of a neighboring carboalkoxy compared to a hydroxymethyl group (Eq. 43).137... 

Recently, Schaumann et al. 153,154 an(j Bienz et tf/.155,156 have developed dependable routes for the resolution of racemic functionalized organosilanes with Si-centered chirality using chiral auxiliaries, such as binaphthol (BINOL), 2-aminobutanol, and phenylethane-l,2-diol (Scheme 2). For instance, the successive reaction of BINOL with butyllithium and the chiral triorganochlorosilanes RPhMeSiCl (R = /-Pr, -Bu, /-Bu) affords the BINOL monosilyl ethers 9-11, which can be resolved into the pure enantiomers (A)-9-ll and (7 )-9-11, respectively. Reduction with LiAlFF produces the enantiomerically pure triorgano-H-silanes (A)- and (R)-RPhMeSiH (12, R = /-Pr 13, -Bu 14, /-Bu), respectively (Scheme 2). Tamao et al. have used chiral amines to prepare optically active organosilanes.157... 

The base-catalyzed hydration of 2-phenyloxirane involves nucleophilic attack preferentially at C(3) (0-C(3) cleavage), but with only partial regio-selectivity. Acid-catalyzed hydration is mainly by 0-C(2) cleavage. The hydration of 2-phenyloxirane catalyzed by epoxide hydrolase is characterized by its very high regioselectivity for the less-hindered, unsubstituted C(3) [175] [176], involving retention of configuration at C(2). In other words, (R)-and (5)-2-phenyloxirane are metabolized to (/ )- and (S)-l-phenylethane-l,2-diol (10.118), respectively. Substrate enantioselectivity was also character-... 

For instance, styrene oxide was resolved by whole cells of Aspergillus niger and Beauveria bassiana via two different pathways showing matching enantio- and regioselectivities with excellent results (Scheme 8). Combination of the two biocatalysts employing a deracemization process in a single reactor led to R) phenylethane-l,2-diol as the sole product in 98% ee and 85% isolated yield [58]. 

Phenylacetaldehyde can be obtained in high yield by vapor-phase isomerization of styrene oxide, for example, with alkali-treated silica-alumina [147]. Another process starts from phenylethane-l,2-diol, which can be converted into phenylacetaldehyde in high yield. The reaction is performed in the vapor phase in the presence of an acidic silica alumina catalyst [148]. 

To a flask containing 6.9 gm (0.05 mole) of phenylethane-l,2-diol in 25 ml of chloroform is added dropwise at room temperature 5.95 gm (0.05 mole) of thionyl chloride. After the initial reaction in which hydrogen chloride is evolved, the solution is refluxed for 1 hr. The solution is cooled, washed with water, then with 2 % sodium bicarbonate solution, dried, and distilled to afford 5.7 gm (62%) b.p. 62°-64°C (0.15 mm), n 4-6 1.5421. 

Stilbene is also converted into the epoxide and the preparation of the lsO-isomcr 3 in high isotopic purity can also be performed, while 1,1-diphenylethene is transformed to 1.1-di-phenylethane-l,2-diol (4),8 and (T)-stilbene to a mixture of benzophenone9 and //wo-2-fluoro-1.2-diphenylethanol. Fluoro-substituted alkenes can also be converted with a hypofluorous acid/acetonitrile mixture into epoxides 5 in high yield.10... 

Because organobismuth(V) compounds have found considerable use as oxidizing agents, the oxidizing ability of methyl di-l-naphthylbismuthinate [124066-66-6], C21H17Bi02, was investigated. Benzoin yields benzil, naphthalene, and metallic bismuth hydrazobenzene yields azobenzene, and 1,1,2,2-tetraphenylethanediol yields benzophenone. 1,2-Diphenyl-1,2-ethanedione dihydrazone gives diphenylacetylene in 50% yield. Cyclohexane-1,2-diol and 1-phenylethane-l,2-diol, however, were unaffected. 

Other 1,2-diols have also been examined. Phenylethane-l,2-diol has been oxidised using a colloid-derived Au/C catalyst (dAu = 7nm) to mandelic acid (C6HsCH(0H)C02H), an important pharmaceutical intermediate.84,85... 

Using phenylethane-l,2-diol as a substrate, however, a new selectivity scenario appeared owing to a strong induction effect of the phenyl group. In fact, according to Scheme 13.4, two abundant by-products, namely benzoate and phenylglyoxylate, were detected beside the expected mandelate, working in the presence of NaOH. 

Scheme 13.6 Reaction pathway of phenylethane-l,2-diol oxidation at pH 7.

Cyclohexanone oxime dissolved in ca. 2 M NaOH containing NaBH4, and refluxed 2 hrs. cyclohexanol. Y 87%. - Similarly via the Na-salt of the boric acid diester a-Hydroximinoacetophenone l-phenylethane-l,2-diol. Y 72-78%. -Oximes of conjugated carbonyl compds., such as cinnamaldehyde or acetophenone, do not react. F. e. s. K. H. Bell, Australian J. Chem. 23, 1415 (1970). 

Diphenylpropane-l, 2-diol, A51.8 l-Tolyl-2-phenylethane-l,2-diol, A"14.2, A"14.5 3-Methyl-2-(l-naphthyl)butyric acid, A"45.9 3-Methyl-2-(2-naphthyl)butyric acid, A"45.10 Catalpone, Y"15.4... 

TBDMSCl has been used to selectively protect the primary hydroxyl group of 1,2- and 1,3-diols under mild conditions, via dibutylstannylene acetal intermediates. For example, treatment of the dibutylstannylene acetal of l-phenylethane-l,2-diol with TBDMSCl in chloroform affords the primary ether in excellent yield (eq 27). This selectivity for the primary hydroxyl group is different from acylation or alkylation of dibutylstannylene acetal... 

A diphenylpolystyryldiethoxyphosphorane (24), prepared from a DF =1.0 PS-diphenylphosphine and diethyl peroxide, was more stable and easier to handle than the diethoxytriphenylphos-phorane. The polymeric reagent cyclodehydrated diols to three-, five- and six-membered ethers in yields as high as the solution reagent, and converted 1,2-diols to epoxides stereoselectively. For example, S( + )-phenylethane-l,2-diol gives 68% enantiomeric excess (ee) S(4-)-styrene oxide as shown in equation (8), whereas only the racemic product was obtained from the soluble reagent. 

Rui, L., Cao, L., Chen, W., Reardon, K.F. and Wood, T.K. (2005) Protein engineering of epoxide hydrolase from Agrobacterium radiohacter ADI for enhanced activity and enantioselective production of (R)-l-phenylethane-l,2-diol. Appl. Environ. Microbiol., 71,3995-4003. 

Phenylethane-l,2-diol, A22.13 Norbornenecarboxylic acids, A47.il 6-Hydroxycyclohex-2-ene-l-acetic acid lactone,... 

The matching enantiopreference and regioselectivity of B. bassiana and A. niger allowed the development of an elegant deracemization technique. Thus, combination of both strains in a single reactor led to the formation of (i )-phenylethane-l,2-diol as the sole product in 89% e.e. and 92% isolated yield from ( )-styrene oxide [98] (Scheme 10). 

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