Formation and fate of benzimidazole-based quinone methides. Influence of pH on quinone methide fate

1992 ◽  
Vol 57 (22) ◽  
pp. 5874-5878 ◽  
Author(s):  
Edward B. Skibo
Keyword(s):  
Quinone Methide ◽  
Quinone Methides ◽  
Influence Of Ph

A new dehydrogenative [4 + 1] annulation between para-quinone methides (p-QMs) and iodonium ylides for the synthesis of 2,3-dihydrobenzofurans

2018 ◽  
Vol 5 (23) ◽  
pp. 3483-3487 ◽  
Author(s):  
Yan-Jie Xiong ◽  
Shao-Qing Shi ◽  
Wen-Juan Hao ◽  
Shu-Jiang Tu ◽  
Bo Jiang
Keyword(s):  
Quinone Methide ◽  
Quinone Methides ◽  
Iodonium Ylides

A new dehydrogenative [4 + 1] annulation of para-quinone methides (p-QMs) with acyclic and cyclic iodonium ylides has been established, delivering a variety of functionalized 2,3-dihydrobenzofurans with the retention of the quinone methide unit in generally good yields.

Solvolysis and ring closure of quinone methides photogenerated from biaryl systems

2005 ◽  
Vol 83 (9) ◽  
pp. 1306-1323 ◽  
Author(s):  
Yijian Shi ◽  
Peter Wan
Keyword(s):  
Ring Closure ◽  
Quinone Methide ◽  
High Yield ◽  
Nanosecond Laser ◽  
Quinone Methides ◽  
Molecular Mechanics Calculations ◽  
Fluorescence Studies ◽  
Long Wavelength ◽  
Thermal Chemistry ◽  
Nanosecond Laser Photolysis

A variety of biaryl quinone methides have been photogenerated with a range of efficiencies from biaryl precursors 4–6 and 8, 10, and 11, all having hydroxyl and hydroxymethyl substituents on alternate rings. These novel biaryl quinone methides, which cannot be readily generated via thermal chemistry, are trapped by added nucleophiles such as MeOH and ethanolamine; two that cannot undergo electrocyclic ring closure (from 8 and 11) are readily observable by nanosecond laser photolysis, with long wavelength maxima (λmax) of 600 and 520 nm, respectively. Photogenerated o,o′-biaryl quinone methides undergo electrocyclic ring closure to give the corresponding chromene (pyran) products in high yield. Since the precursor biaryl alcohols have highly twisted structures in the ground state (dihedral angle of up to 90° by molecular mechanics calculations), a significant twisting motion to planarity is required to achieve reaction. Using steady-state fluorescence studies, we present evidence to suggest that the mechanism of quinone methide formation may occur via one of the following mechanisms: (i) dissociation of the proton from ArOH that precedes twisting; or (ii) ArOH dissociation and twisting taking place either simultaneously or in quick succession.Key words: biaryl quinone methide, photosolvolysis, photodeprotonation, photocyclization.

[4+n] Annulation Reactions Using ortho-Halomethyl Anilines as Aza-ortho-Quinone Methide Precursors

Synthesis ◽  
2021 ◽  
Author(s):  
Xiao-Yu He ◽  
Yu-Hong Ma ◽  
Qing-Qing Yang ◽  
Wen-Jing Xiao
Keyword(s):  
Convenient Method ◽  
Reactive Intermediates ◽  
Quinone Methide ◽  
Synthetic Chemistry ◽  
Important Class ◽  
Quinone Methides ◽  
Aniline Derivatives

Aza-ortho-quinone methides are an important class of reactive intermediates, which have found broad applications in synthetic chemistry. Recently, 1,4-elimination of ortho-halomethyl aniline derivatives has emerged as a new powerful and convenient method for aza-ortho-quinone methide generation. This review will highlight their recent applications as aza-ortho-quinone methide precursors in annulation reactions to access various biologically important nitrogen-containing heterocycles. The general mechanisms are briefly discussed as well.

Moving Past Quinone-Methides: Recent Advances toward Minimizing Electrophilic Byproducts from COS/H2S Donors

2021 ◽  
Vol 21 ◽  
Author(s):  
Michael Pluth
Keyword(s):  
Hydrogen Sulfide ◽  
Carbonic Anhydrase ◽  
Therapeutic Potential ◽  
Carbonyl Sulfide ◽  
Quinone Methide ◽  
Quinone Methides ◽  
On Demand ◽  
Physiological Processes ◽  
Recent Approach ◽  
Alternative Approaches

: Hydrogen sulfide (H2S) is an important biomolecule that plays key signaling and protective roles in different physiological processes. With the goals of advancing both the available research tools and the associated therapeutic potential of H2S, researchers have developed different methods to deliver H2S on-demand in different biological contexts. A recent approach to develop such donors has been to design compounds that release carbonyl sulfide (COS), which is quickly converted to H2S in biological systems by the ubiquitous enzyme carbonic anhydrase (CA). Although highly diversifiable, many approaches using this general platform release quinone methides or related electrophiles after donor activation. Many such electrophiles are likely scavenged by water, but recent efforts have also expanded alternative approaches that minimize the formation of electrophilic byproducts generated after COS release. This mini-review focuses specifically on recent examples of COS-based H2S donors that do not generate quinone methide byproducts after donor activation.

1995 Merck Frosst Award Lecture Quinone methides: relevant intermediates in organic chemistry

1996 ◽  
Vol 74 (4) ◽  
pp. 465-475 ◽  
Author(s):  
Peter Wan ◽  
Beverly Barker ◽  
Li Diao ◽  
Maike Fischer ◽  
Yijian Shi ◽  
...  
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Aqueous Media ◽  
Laser Flash ◽  
Alder Reaction ◽  
Quinone Methide ◽  
Quinone Methides ◽  
Chemical Systems ◽  
The One ◽  
Chroman Ring

ortho and para-Quinone methides (2-methylene-3,5-cyclohexadien-1-one and 4-methylene-2,5-cyclohexadien-1-one, respectively) are intermediates in a variety of important chemical systems. In particular, o-quinone methides are useful in synthesis for the construction of chroman ring systems. A brief account of the relevance of quinone methide chemistry will be provided. This is followed by a review of recent studies from our laboratory on efficient methods for the photogeneration of quinone methides, concentrating on the use of hydroxy-substituted benzyl alcohols in aqueous media. It is shown that this method is general since it provides access to o-, m-, and p-quinone methide isomers. When appropriately substituted, all of these quinone methide isomers have been spectroscopically characterized by laser flash photolysis, making this technique the one of choice for studying the dynamics of these reactive intermediates. The mechanism of photochemical generation from hydroxybenzyl alcohols and extensions of the reaction to photogeneration of fluorenyl and biphenyl quinone methides will also be presented. Key words: quinone methide, biphenyl quinone methide, carbocation, photosolvolysis, photodehydroxylation, hetero-Diels–Alder reaction.

Synthesis of indenofurans, benzofurans and spiro-lactones via Hauser–Kraus annulation involving 1,6-addition of phthalide to quinone methides

2020 ◽  
Vol 18 (29) ◽  
pp. 5677-5687
Author(s):  
Pallabita Basu ◽  
Nishikant Satam ◽  
Irishi N. N. Namboothiri
Keyword(s):  
Ring Opening ◽  
Ring Closure ◽  
Quinone Methide ◽  
Quinone Methides ◽  
Oxygen Heterocycles ◽  
Multiple Ring

Base mediated 1,6-addition–Dieckmann cyclization of phthalide with quinone methide leads to oxygen heterocycles such as indenofurans, spiro-lactones and benzofurans through a cascade of rearrangements involving multiple ring opening and ring closure.

Excited state intramolecular proton transfer in 1-hydroxypyrene

2011 ◽  
Vol 89 (3) ◽  
pp. 433-440 ◽  
Author(s):  
Matthew Lukeman ◽  
Misty-Dawn Burns ◽  
Peter Wan
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Intramolecular Proton Transfer ◽  
Quinone Methide ◽  
Acid Base ◽  
Quinone Methides ◽  
Marked Enhancement ◽  
Theoretical Predictions ◽  
Important Pathway ◽  
Acetonitrile Solutions

1-Hydroxypyrene (1) shows unusual acid–base chemistry in its singlet excited state. Whereas most hydroxyarenes experience a marked enhancement in their acidity when excited, and rapidly deprotonate to give the corresponding phenolate anion, this is not an important pathway for 1, despite theoretical predictions that 1 should experience enhanced acidity as well. In this work, we demonstrate that 1 undergoes a competing excited state intramolecular proton transfer from the OH to carbon atoms at the 3, 6, and 8 positions of the pyrene ring to give quinone methide intermediates. When the reaction is carried out in D2O, reversion of these quinone methides to starting material results in replacement of the ring hydrogens with deuterium, providing a convenient handle to follow the reaction with NMR spectroscopy and mass spectrometry. The quantum yield for the reaction is 0.025 and appears to not be strongly dependent on the water content when aqueous acetonitrile solutions are used. 1-(2-Hydroxyphenyl)pyrene (19) was prepared and studied and shows similar reactivity to 1.

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