Novel generation of an o-quinone methide from 2-(2′-cyclohexenyl)phenol by excited state intramolecular proton transfer and subsequent C–C fragmentation

2002 ◽  
pp. 2636-2637 ◽  
Author(s):  
Julio Delgado ◽  
Amparo Espinós ◽  
M. Consuelo Jiménez ◽  
Miguel A. Miranda
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Intramolecular Proton Transfer ◽  
Quinone Methide

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.

Photogeneration of 1,5-naphthoquinone methides via excited-state (formal) intramolecular proton transfer (ESIPT) and photodehydration of 1-naphthol derivatives in aqueous solution

2004 ◽  
Vol 82 (2) ◽  
pp. 240-253 ◽  
Author(s):  
Matthew Lukeman ◽  
Duane Veale ◽  
Peter Wan ◽  
V Ranjit N. Munasinghe ◽  
John ET Corrie
Keyword(s):  
Aqueous Solution ◽  
Excited State ◽  
Proton Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Intramolecular Proton Transfer ◽  
Photochemical Reactions ◽  
Quinone Methide ◽  
Phenol Derivatives ◽  
Naphthol Derivatives

The photochemistry of naphthols 1, 2, 4, 5 and 9, and phenol 10 has been studied in aqueous solution with the primary aim of exploring the viability of such compounds for naphthoquinone and quinone methide photogeneration, along the lines already demonstrated by our group for phenol derivatives. 1-Naphthol (1) is known to be substantially more acidic than 2-naphthol (2) in the singlet excited state (pKa* = 0.4 and 2.8, respectively) and it was expected that this difference in excited-state acidity might be manifested in higher reactivity of 1-naphthol derivatives for photochemical reactions requiring excited-state naphtholate ions, such as quinone methide formation. Our results show that three types of naphthoquinone methides (26a, 26b, and 27) are readily photogenerated in aqueous solution by irradiation of 1-naphthols. Photolysis of the parent 1-naphthol (1) in neutral aqueous solution gave 1,5-naphthoquinone methide 26a as well as the non-Kekulé 1,8-naphthoquinone methide 26b, both via the process of excited-state (formal) intramolecular proton transfer (ESIPT), based on the observation of deuterium exchange at the 5- and 8-positions, respectively, on photolysis in D2O–CH3CN. A transient assignable to the 1,5-naphthoquinone methide 26a was observed in laser flash photolysis experiments. The isomeric 2-naphthol (2) was unreactive under similar conditions. The more conjugated 1,5-naphthoquinone methide 27 was formed efficiently via photodehydroxylation of 4; isomeric 5 was unreactive. The efficient photosolvolytic reaction observed for 4 opens the way to design related naphthol systems for application as photoreleasable protecting groups by virtue of the long-wavelength absorption of the naphthalene chromophore.Key words: photosolvolysis, excited-state intramolecular proton transfer, quinone methide, photorelease, photoprotonation.

Observation of excited state proton transfer reactions in 2-phenylphenol and 2-phenyl-1-naphthol and formation of quinone methide species

2015 ◽  
Vol 17 (14) ◽  
pp. 9205-9211 ◽  
Author(s):  
Jiani Ma ◽  
Xiting Zhang ◽  
Nikola Basarić ◽  
Peter Wan ◽  
David Lee Phillips
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Transient Absorption ◽  
Intramolecular Proton Transfer ◽  
Quinone Methide ◽  
Transfer Reactions ◽  
Quinone Methides ◽  
Time Resolved ◽  
Excited State Proton Transfer ◽  
Proton Transfer Reactions

Excited state intramolecular proton transfer from a phenol (naphthol) to a carbon atom of the adjacent aromatic ring and formation of quinone methides was studied by femtosecond time-resolved transient absorption.

Mechanistic studies of photohydration of m-hydroxy-1,1-diaryl alkenes

2002 ◽  
Vol 80 (1) ◽  
pp. 46-54 ◽  
Author(s):  
John G Cole ◽  
Peter Wan
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Parent Compound ◽  
Laser Flash ◽  
Intramolecular Proton Transfer ◽  
Quinone Methide ◽  
Quantum Yields ◽  
Nanosecond Laser

The photohydration of a variety of m-hydroxy-1,1-diaryl alkenes (8–10) and related systems (11 and 12) has been studied in aqueous CH3CN solution. All of these alkenes photohydrate efficiently in 1:1 H2O–CH3CN, to give the corresponding 1,1-diarylethanol (Markovnikov addition) products with high chemical and quantum yields. The aim of this study was to further probe the mechanism of photohydration reported for the parent m-hydroxy-α-phenylstyrene (5), which has been proposed as consisting of a water trimer-mediated excited state (formal) intramolecular proton transfer (ESIPT) from the phenolic proton to the β-carbon of the alkene moiety to give an observable (by laser flash photolysis (LFP)) m-quinone methide intermediate 6. For this purpose, derivatives of 5 with substituents (methyl or methoxy) on the α-phenyl ring as well as related model compounds were explored. Product studies, quantum yields, fluorescence, and nanosecond laser flash data are reported that are consistent with two distinct mechanisms for photohydration of these compounds: one involving water-mediated ESIPT (8, 9), as observed for the parent compound 5, and one involving direct protonation of the β-carbon by solvent water (11 and 12), with compound 10 possibly operating via both mechanisms.Key words: photohydration, solvent-assisted excited state intramolecular proton transfer (ESIPT), m-quinone methide, diarylmethyl carbocation.

scholarly journals An enhanced sampling QM/AMOEBA approach: The case of the excited state intramolecular proton transfer in solvated 3-hydroxyflavone

2021 ◽  
Vol 154 (18) ◽  
pp. 184107
Author(s):  
Michele Nottoli ◽  
Mattia Bondanza ◽  
Filippo Lipparini ◽  
Benedetta Mennucci
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Intramolecular Proton Transfer ◽  
Enhanced Sampling
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