Quinone Methide Intermediates from the Photolysis of Hydroxybenzyl Alcohols in Aqueous Solution

Diao, Li; Yang, Cheng; Wan, Peter

doi:10.1021/ja00124a024

Cited by 149 publications

(139 citation statements)

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“…Our observation of continuing acid catalysis of o-quinone methide hydration well up into the concentrated acid region is at variance with a report that flash photolytic generation of the α-phenyl derivative (4) in acidic solutions gave a signal that decreased in intensity with increasing acidity and was lost completely at acidities greater than pH = 1 [1,3]. This difference suggests that the hypothesis advanced on the basis of this signal loss, viz.…”

Section: Mechanism Of the Photoreactioncontrasting

confidence: 79%

“…We generated this substance using a photoreaction developed by Peter Wan, which, as shown in eq. 1, produces o-quinone methide by dehydration of o-hydroxybenzyl alcohol [1,3]. Flash photolysis of this alcohol in aqueous solution generated a transient species with the strong absorbance at λ = 400 nm that is characteristic of oquinone methide [4].…”

Section: O-quinone Methidementioning

confidence: 99%

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Reactive intermediates. Some chemistry of quinone methides

Chiang

Kresge

Zhu

2000

Pure and Applied Chemistry

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Quinone methides were produced in aqueous solution by photochemical dehydration of o-hydroxybenzyl alcohols (o-HOC 6 H 4 CHROH; R = H, C 6 H 5 , 4-CH 3 OC 6 H 4 ), and flash photolytic techniques were used to examine their rehydration back to starting substrate as well as their interaction with bromide and thiocyanate ions. These reactions are acid-catalyzed and show inverse isotope effects (k H+ /k D+ < 1), indicating that they occur through preequilibrium protonation of the quinone methide on its carbonyl carbon atom followed by rate-determining capture of the benzyl carbocations so formed by H 2 O, Br -, or SCN -. With some quinone methides (R = C 6 H 5 and 4-CH 3 OC 6 H 4 ) this acid catalysis could be saturated, and analysis of the data obtained in the region of saturation for the example with R = 4-CH 3 OC 6 H 4 produced both the equilibrium constant for the substrate protonation step and the rate constant for the rate-determining step. Energy relationships comparing the quinone methides with their benzyl alcohol precursors are derived.

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Section: Mechanism Of the Photoreactioncontrasting

confidence: 79%

Section: O-quinone Methidementioning

confidence: 99%

Reactive intermediates. Some chemistry of quinone methides

Chiang

Kresge

Zhu

2000

Pure and Applied Chemistry

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“…as obtained by chemical synthesis or flash photolysis of the corresponding phenols (22)(23)(24)(25)(26). However, spectra of the p-quinone methides of vanillyl alcohol and 4-(methoxymethyl)phenol have never been described.…”

Section: Discussionmentioning

confidence: 99%

Catalytic Mechanism of the Oxidative Demethylation of 4-(Methoxymethyl)phenol by Vanillyl-Alcohol Oxidase

Fraaije

Berkel

1997

Journal of Biological Chemistry

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The catalytic mechanism for the oxidative demethylation of 4-(methoxymethyl)phenol by the covalent flavoprotein vanillyl-alcohol oxidase was studied. ). The kinetic data for the oxidative demethylation of 4-(methoxymethyl)phenol are in accordance with a ternary complex mechanism in which the reduction rate is rate-limiting. It is proposed that, upon reduction, a binary complex is produced composed of the p-quinone methide of 4-(methoxymethyl)phenol and reduced enzyme.

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“…It thus appears very likely that transient X can indeed be assigned as a mixture of probably two stereoisomers of neutral iminoquinone methide 3. These intermediates are therefore, in fact, surprisingly short-lived species (τ ഠ 30 µs), [46] much shorter lived than o-quinone methide, [12,13] and even shorter lived than didehydroazepine 5. This was also observed in the low-temperature studies presented previously: [1] If an organic glass containing both the didehyScheme 5 droazepine 5 and iminoquinone methides sa-3 ϩ aa-3 is thawed, sa-3 and aa-3 disappear before 5.…”

Section: Identification Of Transient Xmentioning

confidence: 99%

“…[23] In order to obtain absolute kinetic data on this interesting system, an efficient photochemical precursor for o-quinone methide would be required. The hydroxybenzyl alcohols used by Wan et al, [12,13,24,25] however, require excitation with λ exc ϭ 248 or 266 nm, which precludes quenching studies with DNA bases. Aryl azides, on the other hand, may be conveniently excited using the 3rd harmonic of an Nd-YAG laser at λ exc ϭ 355 nm.…”

Section: Introductionmentioning

confidence: 99%

A Laser Flash Photolysis Study on 2-Azido-N,N-diethylbenzylamine − The Reactivity of Iminoquinone Methides in Solution

Bucher¹

2001

Eur. J. Org. Chem.

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Photolysis of 2‐azido‐N,N‐diethylbenzylamine (1) in acetonitrile solution in the presence of various quenchers yields products of common nitrene chemistry (that is, derived from a didehydroazepine or a triplet nitrene), together with products arising from trapping of stereoisomeric iminoquinone methides. These intermediates are formed in a monophotonic process, by dediazotation of the precursor combined with a 1,4‐hydrogen shift. The reactivity of the iminoquinone methides (IQM) towards a variety of quenchers, including dienophiles and various nucleophiles, has been explored, using acetonitrile, DMF, and n‐hexane as solvents. IQM reacts efficiently with electron deficient dienophiles [kq(maleic anhydride) = 2.4·107 M−1 s−1], but not with simple olefins such as cyclohexene. IQM shows low to medium reactivity towards simple primary or secondary amines [kq(n‐propylamine) = 6.4·104 M−1 s−1], medium reactivity with sterically unhindered simple alcohols [kq(methanol) = 4.6·106 M−1 s−1], and high to very high reactivity towards thiols [kq(n‐dodecanethiol) = 1.1·109 M−1 s−1], diols, and triols [kq(glycerol) = 1.5·108 M−1 s−1], and sugars [kq(D‐glucose) = 1.0·109 M−1 s−1]. IQM also reacts rapidly with cytosine: kq(cytosine) = 3.4·108 M−1 s−1, while the reaction with adenine or thymine is less efficient [kq(adenine) = 6.4·107 M−1 s−1, kq(thymine) = 7.7·106 M−1 s−1].

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Quinone Methide Intermediates from the Photolysis of Hydroxybenzyl Alcohols in Aqueous Solution

Cited by 149 publications

References 0 publications

Reactive intermediates. Some chemistry of quinone methides

Reactive intermediates. Some chemistry of quinone methides

Catalytic Mechanism of the Oxidative Demethylation of 4-(Methoxymethyl)phenol by Vanillyl-Alcohol Oxidase

A Laser Flash Photolysis Study on 2-Azido-N,N-diethylbenzylamine − The Reactivity of Iminoquinone Methides in Solution

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