P-quinols

Mejorado, L. H. Hoarau, C. Pettus, T. R. R. Diastereoselective dearomatization of resorcinols directed by a lactic acid tether unprecedented enantioselective access to p-quinols. Org. Lett. 2004, 6, 1535-1538. 

Hydroxylation at C-5 or C-l3 has also been successfully achieved by lead tetraacetate oxidation, which was extensively studied in connection with isoquinoline alkaloids by Umezawa s group. (+)-Govanine (96) and (+)-discretine (97) were oxidized with lead tetraacetate in acetic acid to afford 5-acetoxy products 100,101, and 102 via p-quinol acetates (e.g., 99) (Scheme 23)... 

Hydroxyprotoberberine 59a and ( )-corytencine (98) led to 13-acetoxy compounds 104,105, and 107 moreover, the 2,3,9,10,12-pentaoxy-genated protoberberine 108 was also obtained from 98 via the p-quinol acetate 106 through a retro-Mannich reaction followed by recyclization (74,75). Oxidation in dichloromethane instead of acetic acid proceeded differently, namely, 97 and 98 led to pentaoxygenated protoberberines 103 and 109 by introduction of an acetoxyl group at C-4 and C-12, respectively, via o-quinol acetates (76). 

Lead tetraacetate oxidation was applied to construct a benzo[c]-phenanthridine skeleton. The Hofmann degradation product 224 derived from the phenolic protoberberine 59a was oxidized with lead tetraacetate to afford the p-quinol acetate 225, which was cyclized to the benzo[c]-... 

Me3SiCN reacts with both saturated and unsaturated aldehydes and ketones to given silylated cyanohydrines. This reaction has been particularly useful for the regioselective protection of a carbonyl in p. quinones and p. quinol antibiotic metabolite has been prepared. 

Synonyms AI3-00072 Arctuvin p-Benzenediol 1,4-Benzenediol Benzohydroquinone Benzoquinol Black and white bleaching cream BRN 0605970 CCRIS 714 Dihydroxybenzene jO-Dlhydroxybenzene 1,4-Dihydroxybenzene p-Dioxobenzene EINECS 204-617-8 Eldopaque Eldoquin HQ Hydroquinol Hydroquinole a-Hydroquinone p-Hydroquinone 4-Hydroxy-phenol p-Hydroxyphenol NC1-C55834 NSC 9247 Quinol p-Quinol Quinone Tecquinol Tenox HQ Tequinol UN 2662 USAF EK-356. 

Lead tetraacetate in acetic acid oxidizes phenolic 1-benzylisoquinolines to p-quinol acetates which usually rearrange to aporphines in trifluoroacetic acid (25). However, Blasko et al. (24) recently reported that lead tetraacetate oxidized ( )-A -norlaudanosine (34) to dibenzopyrrocoline 35 in 16% yield. 

In the heterocyclic series, racemic 3-(fur-2-yl)alanine has been prepared from furfural using this approach. In addition, (3-(pyrid-3-yl)alanine, ° p-(quinol-3-yl)alanine, ° a p-(benzofuranyl)alanine derivative, 2-amino-3-(2,2 -bipyridi-nyl)propanoic acid, and some interesting derivatives of histidines—in particular 1-alkylhistidines with amphiphilic properties have all been synthesized using this methodology. The complete reaction sequence starting from an aldehyde and an A-acylamino acid derivative is shown in Scheme 7.150. 

Under different reaction conditions, phenols can be oxidized to p-quinones (equations 272600-602 and 273603), but in the case of phenol itself, insufficient selectivity has prevented, as yet, the commercial application of this potentially important synthesis of p-benzoquinone and hydroquin-one. The selectivity of p-benzoquinone, or p-quinol formation can be increased at the expense of oxidative coupling products by using a large excess of the copper reagent [Cu4Cl402(MeCN)3 or CuCl + 02 in MeCN] with respect to the phenolic substrate.604 The suggested mechanism involves the oxidation of the phenoxide radical (189) by a copper(II)-hydroxo species to p-quinol (190) which can rearrange (for R2 = H) to hydroquinone (191 Scheme 14), which is readily oxidizable to p-quinone.6... 

The Carroll rearrangement, a variation on the ester Claisen rearrangement, is a useful method for the preparation of y, 8-unsaturated ketones from allyl acetoacetates, and has been adapted to provide a method for the synthesis of a number of specific arylacetones. Thus, treatment of the p-quinol 1 with diketene and a catalytic amount of DMAP at room temperature gave a 72% yield of the arylacetone 2 together with 5% of the benzofuran 3. 

In general, EC reactions are typically observed according to the following general rank order (by relative ease of oxidation) o,p-quinol and o,p-aminophenol > tertiary amine > m-quinol rv phenol rv arylamine > secondary amine thiol > thioether primary amines, aliphatic alcohols. (HDVs) each redox active metabolite are obtained from the response across adjacent EC-Array sensors. These data are a reflection of the kinetic and thermodynamic components of electron transfer reactions. Since chemical structure is a critical determinant of an analyte s redox behavior, the intrinsic generation of an HDV with EC-Array provides qualitative information for each species. 

Efficient routes to epoxysorbicillinol (26) and bisorbicillinol (27) were developed by Pettus and co-workers [ 103]. The key step is the hypervalent iodine(III)-induced oxidative dearomatization to produce a stable and highly malleable p-quinol intermediate (146) (Scheme 17). 

A catalytic amount of hydrobromic acid with an excess of hydrogen peroxide is found to be an effective reagent for the facile regeneration of carbonyl compounds from their 1,3-dithiane and 1,3-dithiolane derivatives.136 Bromide-assisted oxidation of substituted phenols with hydrogen peroxide, catalysed by heterogenous WO42-ions, resulted in the formation of p-quinols and their ethers in almost quantitative yields.137... 

With water, the reaction was carried out in aqueous acetonitrile at 0°C, but the products (p-quinols) were formed in moderate yield better results were obtained with silylated phenols, especially with their tripropylsilyl ethers [13]. For fluorina-tion, pyridinium polyhydrogen fluoride was the source of fluoride this system was effective with a variety of substrates, including a phenolic steroid [15]. As with DIB, intramolecular cyclizations were also performed on several occasions. 

Dialkyl-l-naphtholsS The p-quinols 1, formed by addition of R Li to the monoadduct of 1,4-naphthoquinone with cyanotrimethylsilane (5, 722), can undergo a second addition of R Li or R2Li to provide the diol 2. Reduction of 2 with HI... 

A full paper has appeared describing the synthesis of the aporphines (34) and (35) through treatment of the p-quinol acetate (33) with trifluoroacetic acid.46 The non-identity of (35) with natural lirinine confirmed structure (36) for lirinine. 

Bunton and Hellyer studied the oxidation of p-hydroxyphenyl acetate and benzoate, 2,5-di-ierl.-butyl-p-quinol, and 3-ferf.-butyl-4-hydroxyphenyl acetate in aqueous solutions in the range pH 0.5-3.0 at 25 °C. The oxidations are second-order (first with respect to each reactant) and in the case of the esters the products are the p-quinone, iodate, and acetic or benzoic acids. The rates of oxidation of p-hydroxyphenyl acetate and benzoate are very similar. The steric effect of the rcrl.-butyl group, substituted into p-quinol and p-hydroxyphenyl acetate, is to reduce the rate by almost the same factor in both cases. Bunton and Hellyer concluded that the mechanisms of oxidation of quinol and its esters by periodate are the same, and that the rate-determining step is the electrophilic attack of either... 

K.L. Sorgi and co-workers prepared acetoacetates from substituted p-quinols and found that they underwent the Carroll rearrangement at room temperature to afford substituted arylacetones and related derivatives in moderate to good yields. ... 

The migration of oxygen from a quaternary center in a cyclohexadienone may be preferred to a carbon shift, when present as an ether or ester function rather than free hydroxy. Thus the p-quinol acetate (117) yields the orcinol monoacetate (118 79%) on treatment at room temperature with trifluoroacetic anhydride, and the p-quinol ether (119) forms the resorcinol diethyl ether (120 71%) in ethanolic sulfuric acid. In the second case, hemiketalization must intervene also some methyl shift (12%) is observed. With the quinol (121), treatment with acetic anhydride-sulfuric acid leads to the lactone (122) acetylation or lactonization probably precedes oxygen shift. A number of related examples can be found in the steroid area. - Thermal 1,3-shifts of p-quinol acetates can also be induced acetate (117) yields catechol acetate (123 50-60%, 45 °C) by way of isomerization of the first-formed acetate (124). In the o-quinol acetate series, 1,2-acetoxy shift is seen in (125) (126 92%) and in (127) (128 90%), both in... 

Upon wanning, the epoxy-p-quinols 3 were obtained. Interestingly, when the p-hy-droperoxide was dissolved in DMF containing t-BuOK, most of 2 reverted instantaneously to 1 with the liberation of oxygen. This indicates the reversibility of the dioxygen addition and the inherent instability of the peroxy anions in absence of suitable solvation. 

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