- A novel Suzuki-type cross-coupling reaction of cyclopropylboronic esters with benzyl bromides
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The Suzuki-type coupling reaction of cyclopropylboronic acids (esters) with benzyl bromides readily takes place by using Ag2O with KOH as the base. The reaction rate and the cross-coupling product yields of cyclopropylboronate esters of ethylene glycol or propane-1,3-diol were higher and better than those of cyclopropylboronic acids. However, the coupling reaction of the cyclopropylboronate esters of glycol with larger substituents was sluggish. The highly optically active benzyl-substituted cyclopropanes could be obtained by the coupling reactions of corresponding optically active cyclopropylboronate esters with benzyl bromides. A novel, ideal method for preparing stereo-defined benzyl-substituted cyclopropanes, especially optically active benzyl-substituted cyclopropanes, is described here.
- Chen, Han,Deng, Min-Zhi
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- Direct gem-difluoromethylenation of sp3-hybridized carbon center through copper-mediated radical/radical cross-coupling for the construction of a CH2-CF2 linkage
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Efficient direct gem-difluoromethylenation of an sp3-hybridized carbon center in benzyl bromides using benzo-1,3-azolic (oxa-, thia- or aza-) difluoromethyl bromides for construction of a CH2-CF2 linkage has been developed through radical/radical C-C cross-coupling via two separate single electron transfer processes (SET) under the promotion of different copper sources.
- Jiang, Haizhen,Xu, Minjun,Lu, Wenjun,Tian, Wenfeng,Wan, Wen,Chen, Yunrong,Deng, Hongmei,Wu, Shaoxiong,Hao, Jian
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- Photolysis of naphtho[b]cyclopropene. Detection of a diradical intermediate
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Photolysis of naphtho[b]cyclopropene in hydrocarbons leads to products derived from hydrogen abstraction by a diradical. Photolysis in a cryogenic matrix allows ESR detection of this diradical, which has zero field splitting parameters D/hc = 0.057, E/hc -1.
- Pan, Weitao,Jones Jr., Maitland,Esat, Burak,Lahti, Paul M.
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- One-Shot Radical Cross Coupling Between Benzyl Alcohols and Alkenyl Halides Using Ni/Ti/Mn System
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A “one-shot” cross coupling between benzyl alcohols and alkenyl halides has been established. A combination of low-valent Ti-mediated C?OH homolysis and the prominent chemistry of Ni-based radical catalysis afforded the desired cross-coupled product with good efficiency. The reaction proceeded regardless of the electronic property of benzyl alcohols, and Ar?B bond remained intact throughout the reaction. Alkenyl bromides with various substitution patterns were applicable to this reaction. Attempts for utilizing sterically demanding tri-substituted alkenes indicated that the steric hinderance mainly inhibited the radical-trapping by Ni species. This reaction can be a simple and efficient strategy for synthesizing densely substituted allylbenzene derivatives. (Figure presented.).
- Suga, Takuya,Takahashi, Yuuki,Ukaji, Yutaka
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supporting information
p. 5622 - 5626
(2020/10/22)
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- Ni-Catalyzed Iterative Alkyl Transfer from Nitrogen Enabled by the in Situ Methylation of Tertiary Amines
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Current methods to achieve transition-metal-catalyzed alkyl carbon-nitrogen (C-N) bond cleavage require the preformation of ammonium, pyridinium, or sulfonamide derivatives from the corresponding alkyl amines. These activated substrates permit C-N bond cleavage, and their resultant intermediates can be intercepted to affect carbon-carbon bond-forming transforms. Here, we report the combination of in situ amine methylation and Ni-catalyzed benzalkyl C-N bond cleavage under reductive conditions. This method permits iterative alkyl group transfer from tertiary amines and demonstrates a deaminative strategy for the construction of Csp3-Csp3 bonds. We demonstrate PO(OMe)3 (trimethylphosphate) to be a Ni-compatible methylation reagent for the in situ conversion of trialkyl amines into tetraalkylammonium salts. Single, double, and triple benzalkyl group transfers can all be achieved from the appropriately substituted tertiary amines. Transformations developed herein proceed via recurring events: The in situ methylation of tertiary amines by PO(OMe)3, Ni-catalyzed C-N bond cleavage, and concurrent Csp3-Csp3 bond formation.
- Nwachukwu, Chideraa Iheanyi,McFadden, Timothy Patrick,Roberts, Andrew George
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p. 9979 - 9992
(2020/09/03)
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- Nickel-Catalyzed Amination of α-Aryl Methyl Ethers
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α-Aryl amines are prevalent in pharmaceutically active compounds and natural products. Herein, we describe a Ni-catalyzed protocol for their synthesis from readily available α-aryl ethers. While α-aryl ethers have been used as electrophiles in Ni-catalyzed C-C bond formations, their use in C-heteroatom bond formation is much less prevalent. Preliminary mechanistic insight suggests that oxidative addition is facilitated by an anionic ligand and that reductive elimination is a reversible process.
- Patel, Purvish,Rousseaux, Sophie A. L.
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p. 492 - 496
(2020/03/13)
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- Low-Valent Titanium-Mediated Radical Conjugate Addition Using Benzyl Alcohols as Benzyl Radical Sources
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A concise method to directly generate benzyl radicals from benzyl alcohol derivatives has been developed. The simple and inexpensive combination of TiCl4(collidine) (collidine = 2,4,6-collidine) and manganese powder afforded a low-valent titanium reagent, which facilitated homolytic cleavage of benzylic C-OH bonds. The application to radical conjugate addition reactions demonstrated the broad scope of this method. The reaction of various benzyl alcohol derivatives with electron-deficient alkenes furnished the corresponding radical adducts.
- Suga, Takuya,Shimazu, Shoma,Ukaji, Yutaka
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p. 5389 - 5392
(2018/09/12)
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- Reductive coupling of benzyl oxalates with highly functionalized alkyl bromides by nickel catalysis
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Coupling reactions involving non-sulfonated C-O electrophiles provide a promising method for forming C-C bonds, but the incorporation of functionalized or secondary alkyl groups remains a challenge due to the requirement for well-defined alkylmetal specie
- Yan, Xiao-Biao,Li, Chun-Ling,Jin, Wen-Jie,Guo, Peng,Shu, Xing-Zhong
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p. 4529 - 4534
(2018/05/28)
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- Intra- and Intermolecular Nickel-Catalyzed Reductive Cross-Electrophile Coupling Reactions of Benzylic Esters with Aryl Halides
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Nickel-catalyzed cross-electrophile coupling reactions of benzylic esters and aryl halides have been developed. Both inter- and intramolecular variants proceed under mild reaction conditions. A range of heterocycles and functional groups are tolerated under the reaction conditions. Additionally, the first example of a stereospecific cross-electrophile coupling of a secondary benzylic ester is described. Crossed off: Nickel-catalyzed cross-electrophile coupling reactions of benzylic esters and aryl halides have been developed. Both inter- and intramolecular variants proceed under mild reaction conditions, and a range of heterocycles and functional groups are tolerated. Additionally, the first example of a stereospecific cross-electrophile coupling of a secondary benzylic ester is described.
- Konev, Mikhail O.,Hanna, Luke E.,Jarvo, Elizabeth R.
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supporting information
p. 6730 - 6733
(2016/06/09)
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- A clean and selective radical homocoupling employing carboxylic acids with titania photoredox catalysis
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A titania photoredox catalysis protocol was developed for the homocoupling of C-centered radicals derived from carboxylic acids. Intermolecular reactions were generally efficient and selective, furnishing the desired dimers in good yields under mild neutral conditions. Selective cross-coupling with two acids proved unsuccessful. An intra-molecular adaptation enabled macrocycles to be prepared, albeit in modest yields. (Chemical Equation Presented).
- Manley, David W.,Walton, John C.
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supporting information
p. 5394 - 5397
(2015/02/19)
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- Unconventional titania photocatalysis: Direct deployment of carboxylic acids in alkylations and annulations
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Under dry, anaerobic conditions, TiO2 photocatalysis of carboxylic acid precursors resulted in carbon-carbon bond-forming processes. High yields of dimers were obtained from TiO2 treatment of carboxylic acids alone. On inclusion of electron-deficient alkenes, efficient alkylations were achieved with methoxymethyl and phenoxymethyl radicals. In reactions with maleic anhydride or maleimides, phenoxyacetic acid produced chromenedione derivatives in addition to adducts. These photocatalytic reactions are simple and cheap to perform, and the TiO2 is easily removed by filtration. The anaerobic photocatalysis strategy offers a range of synthetic possibilities.
- Manley, David W.,McBurney, Roy T.,Miller, Phillip,Howe, Russell F.,Rhydderch, Shona,Walton, John C.
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supporting information; experimental part
p. 13580 - 13583
(2012/10/08)
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- Facile reductive coupling of benzylic halides with ferrous oxalate dihydrate
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Facile reductive coupling of benzylic halides is reported with ferrous oxalate dihydrate in DMF or HMPA under nitrogen atmosphere at 155-160°C. The coupling is proposed to proceed by two successive oxidative additions of benzylic halides to ferrous oxalate to give an intermediate organoiron complex which undergoes concerted dimerization to give the corresponding reductively coupled dimers in high yields.
- Khurana, Jitender M.,Chauhan, Sushma,Maikap, Golak C.
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p. 1737 - 1740
(2007/10/03)
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- Mechanistic investigation of a novel vitamin B12-catalyzed carbon-carbon bond forming reaction, the reductive dimerization of arylalkenes
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In the presence of catalytic vitamin B12 and a reducing agent such as Ti(III)citrate or Zn, arylalkenes are dimerized with unusual regioselectivity forming a carbon-carbon bond between the benzylic carbons of each coupling partner. Dimerization products were obtained in good to excellent yields for mono- and 1,1-disubstituted alkenes. Dienes containing one aryl alkene underwent intramolecular cyclization in good yields. However, 1,2-disubstituted and trisubstituted alkenes were unreactive. Mechanistic investigations using radical traps suggest the involvement of benzylic radicals, and the lack of diastereoselectivity in the product distribution is consistent with dimerization of two such reactive intermediates. A strong reducing agent is required for the reaction and fulfills two roles. It returns the Co(II) form of the catalyst generated after the reaction to the active Co(I) state, and by removing Co(II) it also prevents the nonproductive recombination of alkyl radicals with cob(II)alamin. The mechanism of the formation of benzylic radicals from arylalkenes and cob(I)alamin poses an interesting problem. The results with a one-electron transfer probe indicate that radical generation is not likely to involve an electron transfer. Several alternative mechanisms are discussed.
- Shey, Justin,McGinley, Chris M.,McCauley, Kevin M.,Dearth, Anthony S.,Young, Brian T.,Van der Donk, Wilfred A.
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p. 837 - 846
(2007/10/03)
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- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
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Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
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- Fragmentation of anion radicals with elimination of aryloxy groups
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4-Vinylbenzyl phenyl ether, 4-phenylbenzyl phenyl ether, 1- and 2-naphthylmethyl phenyl ethers react with sodium thiophenolate under photochemical stimulation with replacement of the phenoxy group. The composition of reaction products and relation of reactivity to the structure of substrates is consistent with anion-radical mechanism. The corresponding methoxy and cyano derivatives do not undergo the reaction.
- Dneprovskii,Fedosov
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p. 1438 - 1443
(2007/10/03)
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- A novel photorearrangement of aryl naphthylmethyl ethers. Formation of cyclohexa-2,4-dienone derivatives
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Irradiation of a benzene solution containing 1-methoxycarbonyl-2- naphthylmethyl 2,6-dimethyl substituted phenyl ethers (1a,b) afforded cyclohexa-2,4-dienone derivatives (2a,b) as initial rearranged products via C-O bond cleavage and meta substituted phenols (3a,b) which were formed by subsequent photorearrangement of 2a,b.
- Yoshimi, Yasuharu,Sugimoto, Akira,Maeda, Hajime,Mizuno, Kazuhiko
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p. 4683 - 4686
(2007/10/03)
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- Studies in the Cycloproparene Series: Electron Transfer Induced Dimerizations of Cyclopropanaphthalene
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Attempts to characterize the radical anion from 1H-cyclopropanaphthalene (1) by conventional electron transfer techniques has led instead to detection of the pentacene radical anion (10).- and the pentaphene analogue (11).- by ENDOR spectroscopy.Reactions of (1) with potassium in tetrahydrofuran on a preparative scale depend upon the surface, and 6,13-dihydropentacene (8), 6,7-dihydropentaphene (9), pentacene (10), 2-methylnaphthalene (12) and 1,2-di(2'-naphthyl)ethane (13) are formed.
- Cooney, Mark J.,Halton, Brian,Baumgarten, Martin,Gherghel, Lileta
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p. 1167 - 1174
(2007/10/02)
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- CLEVEAGE RATES FOR RADIOLYSIS-PRODUCED RADICAL ANIONS OF NAPHTHYLMETHYL PHENYL ETHERS AND NAPHTHYL BENZYL ETHERS
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Cleveage reactions of α- and β-naphthylmethyl phenyl ethers and of α- and β-naphthyl benzyl ethers were studied by pulse radiolysis.Transient spectra indicate that reactions occur via electron capture followed by cleavage of the resultant radical anions to give arylmethyl radicals and aryloxide ions.Product studies of extensively irradiated samples are consistent with this scheme and show patterns which are informative for radiation studies in general.The reactions were studied in several solvents.The behavior of transient spectra obtained in acetonitrile for these ethers shows clearly that radical anions of the naphthylmethyl ethers cleave more rapidly than do the radical anions of the naphthyl benzyl ethers.
- Guthrie, Robert D.,Patwardhan, Manjiri,Chateauneuf, John E.
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p. 147 - 152
(2007/10/02)
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- W(CO)6 Mediated C-S Bond Cleavage Reactions
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W(CO)6-mediated reactions of thioethers in refluxing chlorobenzene yielded mainly the corresponding dimers.Optically active thioethers give the respective racemic products.Mercaptans, on the other hand, predominantly afford the corresponding reduced products.A deuterium labeling experiments suggest that the SH group is the hydrogen source in the latter reduction reactions.A free-radical mechanism is suggested.
- Ng, Chi Tat,Wang, Xiaojun,Luh, Tien-Yau
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p. 2536 - 2539
(2007/10/02)
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- Electron Apportionment in Cleavage of Radical Anions. 2. Naphthylmethyl Phenyl Ethers vs. Naphthyl Benzyl Ethers
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Naphthylmethyl phenyl ethers and naphthyl benzyl ethers were found to undergo scission of the H2C-O bond when treated with radical anions of anthracene or fluoranthene.Under comparable conditions, ethers of the naphthylmethyl phenyl series (α and β) reacted more than 10E4 times faster than ethers of the naphthyl benzyl series (α and β).This preference for regioconservation of spin density in the scission process is interpreted in terms of ?-bond polarization at the transition state.
- Maslak, Przemyslaw,Guthrie, Robert D.
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p. 2637 - 2640
(2007/10/02)
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- SPECTROSCOPIC CHARACTERIZATION OF 2-NAPHTHYLCARBENE
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The 308 nm excimer laser flash photolysis of 2-naphthyldiazomethane produces triplet 2-naphthylcarbene (λmax=362 nm) which decays with the observed pseudo-first-order rate constants (kexptl) of 5.54+/-0.03E6; 3.33+/-0.4E6; 1.64+/-0.02E7; and 3.05+/-0.4E6 s-1 in n-pentane, 2,2,4-trimethylpentane (2,2,4-TMP), benzene and Freon 113 respectively.In hydrocarbon solvents the observed decay of triplet 2-naphthylcarbene is correlated with the pseudo-first-order growth of the 2-naphthylmethyl radical (λmax=378 nm).Direct kinetic measurements of the reaction of triplet 2-naphthylcarbene in 2,2,4-TMP with cyclohexane, styrene, meth anol and carbon tetrachloride yielded bimolecular quenching rate constants of 1.48+/-0.04E6; 4.33+/-0.1E7; 7.25+/-0.5E6; and 3.35+/-0.07E6 M-1s-1.It is also found that 2-naphthylcarbene reacts with acetonitrile (kq=5.28+/-0.1E5 M-1s-1) to form a nitrile ylide intermediate with a λmax=372 nm.These results are interpreted in terms of a rapid singlet-triplet-2-naphthylcarbene equilibrium.
- Horn, Keith A.,Chateauneuf, John E.
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p. 1465 - 1470
(2007/10/02)
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- Photoextrusion of SO2 from Arylmethyl Sulfones: Exploration of the Mechanism by Chemical Trapping, Chiral, and CIDNP Probes
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The photochemistry of eight benzylic sulfones, all of which efficiently extrude sulfur dioxide, was studied by a variety of methods.Optically active sulfones (S)-(-)-8, (S)-(-)-11, (S)-(-)-12, (S)-(+)-13, and (R)-(+)-14 were employed to measure the extent of the "hidden" return of the initial photogenerated intermediates by the stereoequilibration of the chiral center.By comparison of the regioisomeric methyl sulfones 11 vs. 13 and 12 vs. 14, preferential C-S bond fragmentation on the naphthyl side was established for the singlet excited sulfones.Added nucleophilic and proton trapping agents had no effect on the course of the reaction, ruling out ionic intermediates.The three hydrocarbon products of photodesulfonation from the unsymmetrical sulfones 8-14 provided a measure of the cage effects, which were highly structure and multiplicity dependent.Rate constants for reaction, and fluorescence, as well as the energy transfer rates from benzophenone were determined.The reaction rate constant for singlet reactivity from the 1-naphthyl sulfones was about three times greater than that for the 2-naphthyl derivatives.CIDNP studies showed a strong product signal for the 1-naphthyl sulfones from desulfonation of a triplet caged radical pair.Naphthaldehyde formation, a very minor, triplet process, was also detected by the CIDNP study of sulfones 9-12.
- Givens, Richard S.,Hrinczenko, Borys,Liu, Jerry H.-S.,Matuszewski, Bogdan,Tholen-Collison, Joan
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p. 1779 - 1789
(2007/10/02)
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- MECHANISTIC STUDIES OF THE PHOTODECOMPOSITION OF ARYLMETHYL SULFONES IN HOMOGENEOUS AND MICELLAR SOLUTIONS.
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The mechanism of photodecomposition of aryl sulfones has been investigated by using both steady-state and time-resolved techniques. Direct evidence for radical and triplet-state intermediates is provided. A correlation is found between the dynamics of reaction of the intermediate triplet states with the stabilities of the intermediate radicals.
- Gould,Tung,Turro,Givens,Matuszewski
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p. 1789 - 1793
(2007/10/02)
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- Synthesis and Reactions of o-Naphthothioquinone Methides
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Photochemical reactions of naphthodithiole-3-thione (7), naphthodithiole-1-thione (10), and naphthodithiole-3-thione (16) with cyclohexene and 2,3-dimethyl-2-butene afford the corresponding naphthothioquinone methides.The thioquinone methide from 7 exists only as a monomeric form and is the first isolable o-thioquinone methide, while that from 16 exists as a dimer of type in the solid state although the chemical behavior suggests the presence of a monomeric form in solution to a very minor extent.In the case of the thioquinone methide from 10, there exists an equilibrium between a monomer and a dimer of type.Some cycloadditions of these thioquinone methides are also described.
- Okazaki, Renji,Sunagawa, Kazuhiko,Kotera, Mitsuharu,Kang, Kyung-Tae,Inamoto, Naoki
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p. 243 - 246
(2007/10/02)
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- THE CHEMISTRY OF QUINOMETHANES. VI. REACTION OF TETRACYANOQUINODIMETHANE WITH METHYL DERIVATIVES OF AROMATIC COMPOUNDS
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In the reaction of tetracyanoquinodimethane with methyl derivatives of aromatic compounds at elevated temperatures, 1,4-bis(dicyanomethyl)benzene and diarylethanes are formed in addition to the normal products from 1,6-addition in the quinoid system of quinodimethane ArCH2C(CN)2C6H4CH(CN)2.Acenaphthene is dehydrogenated by tetracyanoquinodimethane to acenaphthylene.
- Bespalov, B. P.,Getmanova, E. V.
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p. 2017 - 2020
(2007/10/02)
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