1- Benzyl-2-hydroxy

Hexafluoropropyldiethylamine is a particularly useful reagent for conversion of secondary benzylic hydroxy esters into the corresponding secondary benzyl fluorides The reactions proceed with inversion of configuration and a high degree of stereospecificity [86, 87] (equation 53)... 

Fluormation of tertiary benzylic hydroxy esters with the Ishikawa reagent gives somewhat lower yields of fluorides because of the formation of dehydrated products, 2-aryl acrylates [87] (equation 54)... 

The white precipitate is presumably jV,jV-di benzyl hydroxy lamine, an intermediate oxidation product, which disappears after the third catalyst addition. 

N-Benzyl-hydroxy lamin 2 Zu2,42g(20 mMol) Benzaldehyd-oxim tropftman unter Riihren bei 0° 16m/ (32 mMol) 2 m Boran-Losung in abs. THF. Man riihrt 12 Stdn. bei 20 unter Stickstoff. engt i.Vak. ein, versetzt bei 0° mit 10 ml 20%iger Salzsaure, erhitzt 1 Stde. unter RiickfluB und stellt bei 0° mit 10%iger Kalilauge alkalisch. Die Mischung wird 90 Stdn. mit Pentan kontinuierlich extrahiert, im Stickstoff-Strom eingeengt und der Riick-stand bei 20°/0,2 Torr sublimiert Ausbeute 1,28 g (52% d.Th.) F 57°. 

An example of an exclusive chemoselective reduction of a benzylic hydroxy function in a polyfunctional compound is seen in the conversion of 23 into 24... 

It is possible to effect reduction of tertiary benzylic hydroxy functions in the presence of primary halogens. Treatment of 1,1-diphenyl-l-hydroxy-2-haloethanes in chloroform with a slight excess of triethylsilane and a 9- to 10-fold excess of trifluoroacetic acid yields the corresponding 2,2-diphenyl-1-haloethanes (Eq. 45). The yield of the chloride is 77% after one hour at —15°, whereas that of the bromide is 66% following one hour at 0°.184... 

The first example of syn stereoselective expoxidation of arene dihydrodiols was reported in 1981.11 The trans-dihydrodiols 11 and 12, when treated with a 10-fold excess of MCPBA in tetrahydrofuran (THF) at room temperature, gave stereoselectively the syn-diol epoxides 13 and 14, respectively. This stereoselectivity has been ascribed to the operation of steric control by the axial benzylic hydroxy group the equatorial hydroxy group does not exert such control. The isomeric 9,10-epoxides of 7,8-dihydroxy-7,8-dihydro-benzo[a]pyrene can be prepared by the same method.12... 

Imidazolium dichromate is a selective oxidant for allylic and benzylic hydroxy groups. (Allylic alcohols are oxidized faster than benzylic alcohols.) The selectivity over saturate alcohols is similar to that of 4-(dimethylamino)pyridinium chlorochromate. DMF is recommended as the solvent for oxidations, since it appears that the choice of solvent is critical to obtaining high yields. This reagent has also been observed to cause some ( )/(Z)-isomerization during the oxidation of allylic alcohols. 

Sodium periodate is known to oxidize 2-alkylphenols to the corresponding 2-hydroxycyclohexadi-enones. Phenolic benzhydrol-type coriqxiunds (63) follow a rearrangement pathway under foese conditions, and the results are shown in Scheme 17. The benzylic hydroxy group participates in the periodate... 

Amidals 1 were prepared by the reaction of secondary allylic alcohols with benzyl hydroxy-methylcarbamate in dichloromethane using 4-methylbenzenesulfonic acid as a catalyst. The cyclization proceeded by treating 1 with mercury(II) acetate (1.25-2.0 equiv) in acetonitrile at 20 °C for 12 hours, followed by addition of sodium acetate and sodium borohydride to give the corresponding oxazolidine 2 in 60-90% yield158. 

Reduction of l-(4-methylphenyl)ethanol affords a 4 1 mixture of the 2, 5 -dihydro derivative with 4-ethyltoluene," showing again the influence of an electron-releasing substituent in the para position. The result with 4-methoxybenzyl alcohol appears to be completely general. Benzylic hydroxy groups may also be preserved when the proximal aryl ring is hydroxylated, as in the formation of (207 Scheme 42) and in the reduction outlined in Scheme 45." ... 

Yoshikoshi recently reported a 1,3-diol fragmentation (Scheme 14a) under mild conditions, where a benzylic hydroxy group activated by the 2,6-dimethoxy-4-methylphenyl group proved to be a remarkably reactive nucleofuge. 

The hydroformylation of the orf/zo-prop-2-enylphenol 81 which contains no benzylic hydroxy group gives a mixture of the open-chain aldehyde 82 and the seven-membered cyclic hemiacetal 83 in a 82 83 ratio of approximately 40 60 (equation 34) °. The ben-zofuran epoxide 85 and its valence-isomeric quinone methide 86, both readily obtainable from benzofuran 84, rearrange thermally above —20°C to form the allylic alcohol 87 and the tautomeric phenol 88 (equation 35) . ... 

Rao s Alkaloid A (33), C24H27N05, contains four methoxy-groups and one benzylic hydroxy-group and furnishes on hydrogenolysis a tetramethoxy-phenanthroindolizidine isomeric with tylocrebrine (32). Alkaloid C is a phenolic demethyl derivative of A, since it can be converted into Alkaloid A by methylation.15 Hydrogenolysis of Alkaloid C gives Alkaloid B, which can be methylated to the same isomer of tylocrebrine as is obtained by hydrogenolysis of... 

Die hydrierende Aminierung gelingt in vielen Fallen auch unter Erhalt von Ester-, Acetal-, Halogen-, N-Benzyl-, Hydroxy-Gruppen und des Furan-Ringes. 

The first examples of syn stereoselective epoxidation of arene dihydro-diols have been reported with the preparation of (82) and (83) from the corresponding diolsThus unexpected -epoxidation has been interpreted as due to the exertion of steric control by the axial benzylic hydroxy-groups, whereas such control is usually exhibited by equatorial hydroxy-groups. 

Benzylic hydroxy lotion. The 11-oxoestrone derivative (1) is oxidized by DDQ in aqueous dioxane to the ketol (2) in 50% yield. The hydroxyl group has been shown to originate from water. The oxidation is believed to involve an intermediate quinone methide (a). 

As the benzylic hydroxy group in position 7 is removed easily, and further hydroxylation and/or oxidation in other positions can occiu, at least 15 D-ring modifications (5-19) can be distinguished (Fig. 1), which gave rise to nearly 500 natmal anthracyclines isolated to date. However, as the nitrogen-free sugar residues are split off easily already under weakly acidic conditions during the isolation process, not aU of them may be truly natoal. 

CH2OH R = H, CHj. Most D. are didepsides, such as, e.g., atranorin, chloroatranorin, gyrophoric acid, and lecanoric acid. In some D. (e. g., alectorialic acid and barbatolic acid) the acid part (S) is linked with a benzylic hydroxy group of the A part. The structures of about 100 D. isolated from lichens have been elucidated by hydrolysis and alcoholysis to the corresponding carboxylic acids or esters (S part) and to the phenols (A part), respectively. 

The use of Pd/CaCOs provided diol 149 from 148 in high yield without the loss of the benzylic hydroxy group (Scheme 46). Hydrogenolysis of the benzyUc hydroxy group, if necessary, can be accomplished with Pd/C at 75 °C. 

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