Aryl vicinal diols

A vicinal diol 1, when treated with a catalytic amount of acid, can rearrange to give an aldehyde or ketone 3 by migration of an alkyl or aryl group. The prototype of this reaction is the rearrangement of pinacol (R = r2 = = r4 = CH3) to... 

A couple of ortho- and mefa-substituted structures that were regarded as particularly interesting were chosen for re-synthesis on a slightly larger scale with thorough chemical characterization of the isolated inhibitors. In order to decrease the formation of side products detected in the initial library syntheses, it was decided to protect the central vicinal diols of the aryl halide... 

A compound containing an oxygen atom bonded to two alkyl or aryl groups, (p. 500) Synonymous with diol. The term glycol is most commonly applied to the 1,2-diols, also called vicinal diols. (p. 496)... 

All classes of vicinal diols (primary, secondary, tertiary, alkyl- or aryl-substituted) will undergo the pinacol rearrangement, and many acids and solvents have been used for this purpose. Various procedural modifications have been introduced over the years for particular glycols, but sulfuric acid remains the most commonly employed catalyst. The use of 25% H2SO4, as recommended in the procedure of Adams, affords pinacolone in essentially quantitative yield. In some instances better results are obtained when cold concentrated acid is used as the solvent. The choice of reagents and conditions is important, and can completely alter the course of the reaction. For example, pinacol also serves as the starting material for the synthesis of 2,3-dimethylbutadiene, formed by slow distillation of a mixture of the diol and catalytic HBr. ... 

Finally, the hydroxy group may be protected as the tetrahydropyranyl ether, an aryl or alkylllthium reagent added to the carbonyl, and the resulting vicinal diol cleaved to obtain the corresponding g-hydroxy ketone (e.g., eq 4). ... 

In addition to direct oxygenation, e.g. by aryl hydrocarbon hydroxylase, oxidative N- or 0-dealkylation is another process catalyzed by components of the Cytochrome P-450 System (mixed-function oxidases). Reduction also occurs in this system NADPH-cytochrome P-450 reductase has an activity similar to microsomal nitroreductase, i.e. transformation of aronaatic nitro compounds into the corresponding arylamines takes place. The oxidation may be followed by other enzymic reactions, e.g. epoxides are hydrated to vicinal diols by microsomal epoxide hydratase or they are coupled with glutathione by glutathione-S-epoxide transferase. 

Our first elDA was developed for chiral or-hydroxy-carboxylates (Figure 35) and vicinal diols using chiral aryl-boronic acids as receptors. The reversible interaction between arylboronic acids and a-hydroxycarboxylates or diols has been described in the previons section. Our original design is based on the hypothesis that the incorporated stereocenters near the postulated B-N dative bond in the receptors would induce enantioselectivity for the binding between the receptor and two enantiomers of the analyte. However, extensive studies reveal that the proposed B-N dative bond does not exist to an appropriate extent in protic sol vents.A small library of achiral and chiral phenylboronic acids (66, 78-80) was synthesized, and... 

Feringa and coworkers reported a copper-catalyzed O-arylation of dialkyl phosphonates and phosphoramidates with diaryliodonium triflates and 2,6-di-ferf-butylpyridine (DTBP), giving easy access to mixed alkyl aryl phosphonates via elimination of one of the alkyl groups as the alkyl triflate prior to arylation (Scheme 10a) [133]. Aryl(mesityl)iodonium salts reacted in a chemoselective way. Copper-catalyzed arylations of hydroxamic acids [134] and carboxylic acids [135] have also been reported, the latter utilizing thiophosphoramides as cooperative catalysts to allow arylation at room temperature. Onomura s group discovered a Cu-catalyzed monoarylation of vicinal diols in toluene at 100 °C. Only traces of product were obtained with alcohols lacking the vicinal hydroxyl group [136]. 

A three-component synthesis of pyrroles, which unites enolisable ketones, primary amines, and vicinal diols, was reported by Beller. Remarkably, these reactions generate two C-N bonds, one C-C bond, liberate one equivalent of H2, and two equivalents of water in a single synthetic operation. A broad range of substituents is tolerated, including heteroaromatics, esters, amides, and aryl halides. Primary drawbacks of these methods include high reaction temperatures and the inability to access certain regio-isomers, such as 2-ff-3-allqrl pyrroles. 

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