27820-29-7Relevant academic research and scientific papers
Photochemistry of the Stilbenes in Methanol. Trapping the Common Phantom Singlet State
Saltiel, Jack,Gupta, Shipra
, p. 6089 - 6099 (2018)
A comparative study of the photochemistry of cis- and trans-stilbene in methanol shows that both isomers undergo methanol photoaddition giving similar yields of α-methoxybibenzyl in competition with cis-trans photoisomerization. Methanol addition occurs primarily following torsional relaxation of the lowest excited singlet states of each isomer, 1c? and 1t?, to a common twisted singlet excited state intermediate, 1p?, initially called the phantom singlet state. The addition is consistent with the zwitterionic character of 1p?. Ether forms by direct 1,2-addition of CH3OH to the central carbon atoms and by 1,1-addition following rearrangement to 1-benzyl-1-phenylcarbene. Use of CD3OD and GC/MS (gas chromatographic/mass spectroscopic) analysis of the ether products revealed that the ratio of carbene/direct addition pathways is higher starting from cis-stilbene. We conclude that 1p? formed from 1c? is hotter than 1p? formed from 1t?. Surprisingly, except for favoring the carbene pathway, the use of higher energy photons (254 vs 313 nm) does not affect the overall ether quantum yield starting from cis-stilbene but significantly enhances both pathways starting from trans-stilbene. It appears that carbene formation and direct methanol addition to higher trans-stilbene excited state(s) compete with relaxation to S1. Substitution of D for the vinyl Hs of stilbene enhances the direct addition pathway more than 2-fold and strongly suppresses the carbene insertion pathway, revealing a large, kpcd0/kped2 = 6.3, primary deuterium isotope effect in the carbene rearrangement. The 2-fold increase in the ether quantum yield is due primarily to a 2.75-fold increase in the lifetime of 1p? on deuterium substitution of the vinyl hydrogens.
Electrochemical oxidative decarboxylation and 1,2-aryl migration towards the synthesis of 1,2-diaryl ethers
Bu, Faxiang,Hu, Xia,Lei, Aiwen,Lu, Lijun,Wang, Shengchun,Zhang, Heng
, p. 10000 - 10004 (2020/10/06)
Carboxylic acid compounds are important chemicals and are widely present in various natural products. They are not only nucleophiles, but also radical precursors. Classic transition-metal-catalyzed and photochemical decarboxylation have shown their excellent site selectivity in radical chemistry. However, electrochemical decarboxylation with a long history hasn't got enough attention in recent years. In this work, the electrochemical oxidative decarboxylation and 1,2-aryl migration of 3,3-diarylpropionic acids have been introduced to construct C-O bonds with alcohols. Remarkably, this transformation can proceed smoothly without metal catalysts and external oxidants.
The photoredox-catalyzed meerwein addition reaction: Intermolecular amino-arylation of alkenes
Prasad Hari, Durga,Hering, Thea,K?nig, Burkhard
, p. 725 - 728 (2014/01/23)
A variety of amides are efficiently accessible under mild conditions by intermolecular amino-arylation using a photo Meerwein addition with visible light. The reaction has a broad substrate scope, tolerates a large range of functional groups, and was applied to the synthesis of a 3-aryl-3,4- dihydroisoquinoline. From elimination to addition: A variety of amides are efficiently accessible under mild conditions by intermolecular amino-arylation using a photo Meerwein addition with visible light. The reaction has a broad substrate scope, tolerates a large range of functional groups, and was applied to the synthesis of 3-aryl-3,4-dihydroisoquinoline. Copyright
Oxyarylation and aminoarylation of styrenes using photoredox catalysis
Fumagalli, Gabriele,Boyd, Scott,Greaney, Michael F.
supporting information, p. 4398 - 4401 (2013/09/24)
A three-component coupling of styrenes is reported, using photoredox catalysis to achieve simultaneous arylation and C-O or C-N bond formation across the styrene double bond.
Gold-catalysed oxyarylation of styrenes and mono- and gem-disubstituted olefins facilitated by an iodine(III) oxidant
Ball, Liam T.,Lloyd-Jones, Guy C.,Russell, Christopher A.
supporting information; experimental part, p. 2931 - 2937 (2012/04/23)
1-Hydroxy-1,2-benziodoxol-3(1H)-one (IBA) is an efficient terminal oxidant for gold-catalysed, three-component oxyarylation reactions. The use of this iodine(III) reagent expands the scope of oxyarylation to include styrenes and gem-disubstituted olefins, substrates that are incompatible with the previously reported Selectfluor-based methodology. Diverse arylsilane coupling partners can be employed, and in benzotrifluoride, homocoupling is substantially reduced. In addition, the IBA-derived co-products can be recovered and recycled. The I's have it: The unprecedented use of an iodine(III) reagent as the terminal oxidant for gold-catalysed oxyarylation allows the substrate scope to be significantly expanded; in addition to monosubstituted olefins, styrenes and gem-disubstituted olefins are well tolerated (see scheme). With benzotrifluoride as solvent, unproductive homodimerisation of the arylsilane coupling partner is effectively suppressed. Copyright
"Cation pool" method based on C-C bond dissociation. Effective generation of monocations and dications
Okajima, Masayuki,Suga, Seiji,Itami, Kenichiro,Yoshida, Jun-Ichi
, p. 6930 - 6931 (2007/10/03)
The "cation pools" of alkoxyarylcarbenium ions were effectively generated by the oxidative C-C bond dissociation using low temperature electrolysis. The present method is especially effective for the generation and accumulation of dications, which react with carbon nucleophiles. Copyright
The photochemical addition of 2,2,2-trifluoroethanol to methoxy-substituted stilbenes
Roberts, Jeffrey C.,Pincock, James A.
, p. 4279 - 4282 (2007/10/03)
The excited-state lifetime of the trans-stilbene chromophore in acetonitrile is prolonged by methoxy substituents in the meta positions. The long-lived singlet excited state of trans-3,5-dimethoxystilbene (trans-2d) is quenched upon the addition of 2,2,2-trifluoroethanol (TFE), and the Markovnikov ether is observed as the major product from steady-state irradiations. The results indicate that the reaction pathway proceeds through a carbocation intermediate.
Photolysis of α-azidoacetophenones: Direct detection of triplet alkyl nitrenes in solution
Singh, Pradeep N. D.,Mandel, Sarah M.,Robinson, Rachel M.,Zhu, Zhendong,Franz, Roberto,Ault, Bruce S.,Gudmundsdottir, Anna D.
, p. 7951 - 7960 (2007/10/03)
We report the first detection of triplet alkyl nitrenes in fluid solution by laser flash photolysis of α-azido acetophenone derivatives, 1. Azides 1 contain an intramolecular triplet sensitizer, which ensures formation of the triplet alkyl nitrene by bypassing the singlet nitrene intermediate. At room temperature, azides 1 cleave to form benzoyl and methyl azide radicals in competition with triplet energy transfer to form triplet alkyl nitrene. The major photoproduct 3 arises from interception of the triplet alkyl nitrene with benzoyl radicals. The triplet alkyl nitrene intermediates are also trapped with molecular oxygen to yield the corresponding 2-nitrophenylethanone. Laser flash photolysis of 1 reveals that the triplet alkyl nitrenes have absorption around 300 nm. The triplet alkyl nitrenes were further characterized by obtaining their UV and IR spectra in argon matrices. 13C and 15N isotope labeling studies allowed us to characterize the C-N stretch of the nitrene intermediate at 1201 cm-1.
Excited Precursor Reactivity, Fast 1,2-H Shifts, and Diffusion-Controlled Methanol Insertion in 1,2-Diphenylalkylidenes
Motschiedler, Krista,Gudmundsdottir, Anna,Toscano, John P.,Platz, Matthew,Garcia-Garibay, Miguel A.
, p. 5139 - 5147 (2007/10/03)
The photochemistry of several arylalkyldiazo compounds has been investigated by steady-state direct and triplet sensitized irradiations and by nanosecond laser flash photolysis. Steady-state photolyses in methanol yielded methyl ethers and alkenes as the only significant products. Ethers were formed by denitrogenation of the diazo compound followed by carbene insertion into the MeO-H bond, and alkenes were obtained by 1,2-R (R = H,Ph) migrations both in the free carbene and in the singlet excited state of the diazo precursor. Evidence for the exited-state precursor reaction came from differences in product yields as a function of excitation wavelength and excited-state multiplicity. The yields of methyl ethers increased with increasing excitation wavelengths and were greatest upon triplet-state sensitization but were never the sole products formed despite expected diffusion-controlled insertion rates. Accordingly, the formation of pyridine ylides analyzed by laser flash photolysis in the presence of high concentrations of the base yielded relatively modest transient absorptions. The kinetics of the 1,2-H reaction, analyzed by time-resolved detection of stilbene in the case of 1,2-diphenylethylidenes, displayed fast and slow components. The fast component was attributed to stilbene that formed from the excited-state precursor and from the originally formed singlet carbene within the 20 ns pulse. The long-lived component was attributed to a spin-state equilibrated carbene with a lifetime of 70-80 ns in fluorocarbon solvents. Analysis of the long-lived component by a Stern-Volmer treatment upon addition of MeOH gave a lower limit for the reaction rate constant with a value of k1,2-H > 5 × 109 s-1 in a mixed Freon-methanol solvent. It is concluded that the combined effect of phenyl substituents at the carbon bearing the migrating group and high solvent polarity can lead to intramolecular 1,2-H shifts and 1,2-Ph migrations that are fast enough to compete with diffusion-controlled intermolecular MeO-H insertion in concentrated MeOH solutions.
