- Photochemistry of trans-10,11-Dibromodibenzosuberone: A Near-UV Photoacid Generator
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Pulsed laser irradiation of trans-10,11-dibromodibenzosuberone, I, in room-temperature benzene and acetonitrile solutions resulted in efficient debromination to yield dibenzosuberone, II.In benzene, the transient absorption due to the bromine atom (Br.)-benzene ?-complex was observed, while in acetonitrile with added Br- the transient absorption due to Br2.- was detected.In both cases, transient production was instantaneous, indicating that Br. is a primary photoproduct.Transient actinometric experiments using the benzophenone triplet state as a standard and Br2.- as the Br. probe allowed the determination of the quantum yield for Br. production, Φ = 2.4 +/- 0.6.In acetonitrile, in the presence of the H-atom donor, 2-propanol, Br.-Br. recombination to give Br2 competes with H-atom abstraction to yield the acid HBr.Under high-intensity laser irradiation, recombination and H-atom abstraction are competitive, while under low flux laser or UV lamp irradiation, H-atom abstraction is very efficient.In the presence of 1-3 M 2-propanol, acid formation was found to be nearly quantitative.
- Gannon, T.,McGimpsey, W. G.
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- Visible light mediated selective oxidation of alcohols and oxidative dehydrogenation of N-heterocycles using scalable and reusable La-doped NiWO4nanoparticles
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Visible light-mediated selective and efficient oxidation of various primary/secondary benzyl alcohols to aldehydes/ketones and oxidative dehydrogenation (ODH) of partially saturated heterocycles using a scalable and reusable heterogeneous photoredox catalyst in aqueous medium are described. A systematic study led to a selective synthesis of aldehydes under an argon atmosphere while the ODH of partially saturated heterocycles under an oxygen atmosphere resulted in very good to excellent yields. The methodology is atom economical and exhibits excellent tolerance towards various functional groups, and broad substrate scope. Furthermore, a one-pot procedure was developed for the sequential oxidation of benzyl alcohols and heteroaryl carbinols followed by the Pictet-Spengler cyclization and then aromatization to obtain the β-carbolines in high isolated yields. This methodology was found to be suitable for scale up and reusability. To the best of our knowledge, this is the first report on the oxidation of structurally diverse aryl carbinols and ODH of partially saturated N-heterocycles using a recyclable and heterogeneous photoredox catalyst under environmentally friendly conditions.
- Abinaya, R.,Balasubramaniam, K. K.,Baskar, B.,Divya, P.,Mani Rahulan, K.,Rahman, Abdul,Sridhar, R.,Srinath, S.
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p. 5990 - 6007
(2021/08/24)
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- Substituted 9-Anthraldehydes from Dibenzocycloheptanol Epoxides via Acid-Catalyzed Epoxide Opening/Semipinacol Rearrangement
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Starting from benzaldehyde derivatives, the corresponding dibenzocycloheptenol could be prepared in five steps. Under both substrate (secondary vs tertiary alcohol and the substituents on the aromatic ring(s)) and condition control, the subsequent epoxidation and acid-catalyzed epoxide opening/semipinacol rearrangement/aromatization afforded the corresponding 9-anthraldehydes in good yields, up to 88% over two steps. The presence of the electron-withdrawing group(s) on the aromatic ring(s) suppressed the rate of the epoxidation while the subsequent semipinacol rearrangement step required heating; the presence of the electron-donating group(s), on the other hand, frequently led to the decomposition during the epoxidation. From the mechanistic studies, the semipinacol rearrangement of the epoxide could precede the ionization at the bisbenzylic position, yielding the aldehyde intermediate. The ensuing dehydrative aromatization led to the formation of 9-anthraldehyde. Conversely, nucleophilic addition to the aldehyde and dehydrative aromatization with concomitant loss of formic acid led to anthracene.
- Phumjan, Tanawat,Songthammawat, Poramate,Jongcharoenkamol, Jira,Batsomboon, Paratchata,Ruchirawat, Somsak,Ploypradith, Poonsakdi
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p. 13322 - 13349
(2021/09/13)
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- Nitrosoarene-Catalyzed HFIP-Assisted Transformation of Arylmethyl Halides to Aromatic Carbonyls under Aerobic Conditions
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A rare metal-free nucleophilic nitrosoarene catalysis accompanied by highly hydrogen-bond-donor (HBD) solvent, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), organocatalytically converts arylmethyl halides to aromatic carbonyls. This protocol offers an effective means to access a diverse array of aromatic carbonyls with good chemoselectivity under mild reaction conditions. The activation of arylmethyl halides by HFIP to generate stable carbocation and autoxidation of in situ generated hydroxylamine to nitrosoarene in the presence of atmospheric O2 are the keys to success.
- Pradhan, Suman,Sharma, Vishali,Chatterjee, Indranil
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supporting information
p. 6148 - 6152
(2021/08/03)
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- BROMINE FREE PREPARATION OF 5H-DIBENZO [A,D] CYCLOHEPTEN-5-ONE
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The invention relates to a convenient procedure for the preparation of 5H- Dibenzo[a,d] cyclohepten-5-one in high yield an purity from 10,11-Dihydro-5H-dibenzo[a,d]cyclohepten-5-one. The procedure is not only convenient to be adopted on an industrial scale but also safe and environment friendly.
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Page/Page column 6
(2020/03/23)
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- CO2-Catalyzed oxidation of benzylic and allylic alcohols with DMSO
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CO2-catalyzed transition-metal-free oxidation of alcohols has been achieved. Earlier, several methodologies have been explored for alcohol oxidations based on transition-metal catalysts. However, owing to the cheaper price, easy separation and nontoxicity, transition-metal-free systems are in high demand to the pharmaceutical industries. For this reason, various primary and secondary alcohols have been selectively oxidized to the corresponding carbonyl compounds using CO2 as a catalyst in the presence of different functional groups such as nitrile, nitro, aldehyde, ester, halogen, ether, and so on. At the end, transition-metal-free syntheses of pharmaceuticals have also been achieved. Finally, the role of CO2 has been investigated in detail, and the mechanism is proposed on the basis of experiments and DFT calculations.
- Riemer, Daniel,Mandaviya, Bhavdip,Schilling, Waldemar,G?tz, Anne Charlotte,Kühl, Torben,Finger, Markus,Das, Shoubhik
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p. 3030 - 3034
(2018/04/14)
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- Rapid and efficient debromination of vic-dibromides with VCl3/indium system
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The VCl3/In system was found to be a new protocol for debromination of a variety of vic-dibromides to the corresponding alkenes in high yields with short reaction times under mild conditions. This new methodology is highly chemose-lective, tolerating several functional groups such as chloro, bromo, fluoro, keto, ester, carboxyl, and methoxy groups.
- Woo Yoo, Byung,Yeon Park, Jee,Jong Shin, Hyo
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p. 275 - 278
(2018/08/21)
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- Metal-free oxidation of secondary benzylic alcohols using aqueous TBHP
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We report a simple, yet efficient metal-free oxidation of secondary benzylic alcohols in the presence of t-butyl hydroperoxide (70% TBHP) with high yields of up to 98%. This type of reaction can be carried out using a wide variety of substrates, requires no other organic solvent, and proves to be tolerant toward a variety of different functional groups.
- Wu, Jianglong,Liu, Yan,Ma, Xiaowei,Liu, Ping,Gu, Chengzhi,Dai, Bin
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supporting information
p. 1747 - 1758
(2016/10/30)
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- Activation of DMSO for Swern-type oxidation by 1,1-dichlorocycloheptatriene
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A new dimethylsulfoxide activation method employing 1,1-dichlorocycloheptatriene has been developed for a mild Swern-type oxidation of a variety of alcohols. The carbonyl products can be obtained in good to excellent yields from this operationally simple and efficient method. This work is the first report of dimethylsulfoxide activation by a simple chlorinated hydrocarbon reagent, which has the unique ability of equilibrating to its reactive aromatic cationic form.
- Nguyen, Thanh Vinh,Hall, Michael
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supporting information
p. 6895 - 6898
(2015/01/09)
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- Photocatalytic dehalogenation of vicinal dibromo compounds utilizing sexithiophene and visible-light irradiation
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The reductive dehalogenation of a variety of vicinal-dibromide compounds has been accomplished through the use of α-sexithiophene as an organophotocatalyst. This photocatalytic system brings about the desired transformations in good yields, using low catalyst loadings and short reaction times. To help shed light on the efficiency of this process, we have studied the kinetics of the key mechanistic steps utilizing a combination of steady-state/time-resolved fluorescence and laser flash photolysis techniques.
- McTiernan, Christopher D.,Pitre, Spencer P.,Scaiano, Juan C.
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p. 4034 - 4039
(2015/02/19)
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- Photolysis of dibenzo[a,d]cycloheptene dimer
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Photolysis reaction of dibenzo[a,d]cycloheptene dimer 3 provides three dibenzo[a,d]cycloheptyl dimmers 4, 5 and 6 under different irradiation conditions via the intramolecular degradative cyclodimerization. A tetracyclic benzo[4,5]cyclohepta[1,2,3-de]naphthalene core is also synthesized.
- Chang, Meng-Yang,Huang, Yu-Ping
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p. 632 - 638
(2013/10/22)
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- Iodine-catalyzed disproportionation of aryl-substituted ethers under solvent-free reaction conditions
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Iodine was demonstrated to be an efficient catalyst for disproportionation of aryl-substituted ethers under solvent-free reaction conditions. Variously substituted 1,1,1′,1′-tetraaryldimethyl ethers were transformed into the corresponding diarylketone and diarylmethane derivatives. I 2-catalyzed transformation of 4-methoxyphenyl substituted ethers yielded mono- and dialkylated Friedel-Crafts products as well. Treatment of trityl alkyl and trityl benzyl ethers with a catalytic amount of iodine produced triphenylmethane and the corresponding aldehydes and ketones. The electron-donating substituents facilitated the reaction, while the electron-withdrawing groups retarded it; the difference in reactivity is not very high. Such an observation may be in favour of hydride transfer, predominantly from the less electron rich side of the ether with more stable carbocation formation. With the isotopic studies it was established that a substantial portion of the C-H bond scission took place in the rate-determining step, while the carbonyl oxygen atom originated from the starting ether, and not from the air. The transformation took place under air and under argon, and HI was not a functioning catalyst.
- Jereb, Marjan,Vrazic, Dejan
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p. 1978 - 1999
(2013/05/22)
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- Facile and efficient method for the debromination of vic-dibromides to alkenes with BiCL3/Ga system
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BiCl3/Ga was found to be a mild, efficient, and chemoselective system for the debromination of a series of functionally and structurally various vic-dibromides. A broad range of functional groups (ester, carboxy, aldehyde, methoxy, chloro, and ketone) was tolerated under the reaction conditions and only trans olefins were obtained in good yields. Copyright Taylor & Francis Group, LLC.
- Yoo, Byung Woo,Kim, Seo Hee,Park, Young Kwang
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experimental part
p. 1632 - 1636
(2012/05/05)
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- Efficient synthesis of carbonyl compounds: Oxidation of azides and alcohols catalyzed by vanadium pentoxide in water using tert-butylhydroperoxide
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Catalytic amount of vanadium reagent with tert-butylhydroperoxide as the oxidant was found to be an excellent oxidizing agent in aqueous medium. Vanadium pentoxide with aq tert-butylhydroperoxide readily oxidizes primary benzylic azides to the corresponding acids and secondary benzylic azides to the corresponding ketones in excellent yields. Further, vanadium pentoxide and aq tert-butylhydroperoxide combination turned out to be an effective catalyst for the oxidation of alcohols. Using vanadium pentoxide and aq tert- butylhydroperoxide primary alcohols were oxidized to the corresponding acids, whereas secondary alcohols underwent a smooth transformation to furnish corresponding ketones in excellent yields. All the oxidations are performed in water.
- Alagiri, Kaliyamoorthy,Prabhu, Kandikere Ramaiah
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experimental part
p. 8544 - 8551
(2011/11/13)
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- Determination of hydride affinities of various aldehydes and ketones in acetonitrile
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Chemical equations presented. The hydride affinities of 21 typical aldehydes and ketones in acetonitrile were determined by using an experimental method, which is valuable for chemists choosing suitable reducing agents to reduce them. The focus of this paper is to introduce a very facile experimental method, which can be used to determine the hydride affinities of various carbonyl compounds in solution.
- Zhu, Xiao-Qing,Chen, Xi,Mei, Lian-Rui
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supporting information; experimental part
p. 2456 - 2459
(2011/07/09)
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- Flow-vacuum pyrolysis of dibenzocycloheptane derivatives on zeolites catalysts. IV
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The pyrolysis of 10,11-dihydro-5H-dibenzo[a,d]cicloheptadien-5-ol (4) and of 5H-dibenzo[a,d]cycloheptatrien-5-ol (5) in flowvacuum conditions (advanced vacuum, inert atmosphere) on zeolites at 300°C is presented. The reaction products were identified by GC/MS using authentic samples and a reaction mechanisms involving cationic species as intermediates were proposed. A comparison with the pyrolysis of the same compounds performed in FVP conditions on quartz is presented.
- Istrati, Daniela,Parvulescu, Luminitza,Popescu, Angela,Mihaiescu, Dan,Badea, Florin
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p. 711 - 714
(2011/10/02)
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- Mild and efficient debromination of vic-dibromides to alkenes with fecl36h2o/indium system
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The FeCl36H2O/indium system efficiently causes debromination of various dibromides to the corresponding alkenes in good to excellent yields under mild conditions.
- Woo Yoo, Byung,Woo Choi, Jin,Hye Yang, Min
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experimental part
p. 1488 - 1493
(2009/09/27)
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- Dimethyl sulfoxide mediated elimination reactions in 3-aryl 2,3-dihalopropanoates: Scope and mechanistic insights
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(Chemical Equation Presented) Dimethyl sulfoxide (DMSO) efficiently causes the reductive elimination of 3-aryl 2,3-dibromopropanoates to cinnamates with good yield. With 3-phenyl 2,3-dihalopropanoates, debromination is the major pathway providing 3-phenylacrylate derivatives in high yields, whereas dehydrobromination is a competing pathway with thiophene derivatives. 1H NMR, 81Br NMR, and MS techniques indicated the formation of brominated-DMSO, MeBr, and HBr as byproducts in this transformation with no evidence for the formation of Br2. The dual role of DMSO as a nucleophile and bromine scavenger accounts for the products formed in this reaction.
- Li, Wei,Li, Jianchang,Lin, Melissa,Wacharasindhu, Sumrit,Tabei, Keiko,Mansour, Tarek S.
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p. 6016 - 6021
(2008/02/10)
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- Novel deoxygenation reaction of epoxides by indium
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A novel, mild, ecofriendly protocol for the deoxygenation of epoxides to alkenes using indium metal and indium(I) chloride or ammonium chloride in alcohol has been developed. It was necessary for the presence of good radical-stabilizing groups adjacent to the oxirane ring for the deoxygenation reaction to occur. It is proposed that this reaction occurs through an SET process with indium as an electron donor.
- Mahesh, Mohan,Murphy, John A.,Wessel, Hans Peter
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p. 4118 - 4123
(2007/10/03)
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- Efficient heterogeneous oxidation of alkylarenes with molecular oxygen
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(Chemical Equation Presented) Ru(OH)x/Al2O 3 efficiently catalyzes the heterogeneous aerobic oxygenation or oxidative dehydrogenation of alkylarenes to give the corresponding oxygenated or dehydrogenated products. Catalyst/product separation is very easy, and the recovered catalyst is reusable with retention of the high catalytic performance.
- Kamata, Keigo,Kasai, Jun,Yamaguchi, Kazuya,Mizuno, Noritaka
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p. 3577 - 3580
(2007/10/03)
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- Flow-vacuum pyrolysis of polycyclic compounds. 151 pyrolysis of three RELATED dibenzocycloalkanols
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The flow-vacuum pyrolyses of cis-9,10-bis(hydroxymethyl)-9,10-dihydroanthracene (4); 6H-5,7-dihydrodibenzo[a,c]cyclohepten-6-ol (5) and 5H-dibenzo[a,d]cyclohepten-5-ol (6) were studied at 1.33 mbar in argon atmosphere over a large temperature interval. The main pyrolysis product of 4-cis was anthracene (13), accompanied by traces of 9-methylanthracene (15) and 9-anthraldehyde (14). The main pyrolysis products of 5 were: 9-methylphenanthrene (17) and 5H-dibenzo[a,c]cycloheptene (16), whereas phenanthrene (19) and fluorene (18) were minor products. From the flow-vacuum pyrolysis of 6 the corresponding ketone (dibenzosuberenone 12) and 5H-dibenzo[a,d]cycloheptene (20) were the major products and anthracene and 9-methylanthracene the minor ones. The thermal behavior of 4-cis, 5 and 6 was rationalized on the basis of mechanisms including radical and concerted steps. Some parts of the here proposed mechanisms were confirmed by our previous works describing the conversions of authentic 16 and 20 to the same end-products: 17 + 19, respectively 13 + 15. A comparison with the thermal behaviour of other related dibenzocycloalkanols is also made.
- Banciu, Mircea D.,Popescu, Angela,Parvulescu, Lumini?a,Ciuculescu, Crinu,Drǎghici, Constantin,Banciu, Anca,Mihǎiescu, Dan
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p. 239 - 248
(2007/10/03)
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- Solid-support-bound 1-aminoimidazolium chlorochromate: A selective, efficient and recyclable oxidant
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A series of polymer-bound imidazolium chlorochromates have been synthesised and used as selective oxidants for benzylic and cinnamylic alcohols. Solid-support-bound 1-amino-imidazolium chlorochromate proved to be the most convenient system due to its efficiency, selectivity and ease of recycling the material.
- Linares,Sánchez,Alajarín,Vaquero,Alvarez-Builla
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p. 382 - 388
(2007/10/03)
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- A novel catalytic role of molecular iodine in the oxidation of benzylic alcohols: Microwave-assisted reaction
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Molecular iodine was used to catalyse the oxidation of several benzylic alcohols to the corresponding ketones under the microwave-irradiated method, and the role of iodine was explored.
- Mukhopadhyay,Becker,Banik
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- Free and polymer-bound tricyclic azaphosphatranes HP(RNCH2CH2)3N+: Procatalysts in dehydrohalogenations and debrominations with NaH
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The commercially available nonionic base P(CH3NCH2CH2)3N (1a) was shown earlier to be superior to DBU as a stoichiometric reagent for the conversion of primary and secondary alkyl halides to alkenes (Arumugam, S.; Verkade, J.G.J. Org. Chem. 1997, 62, 4827). The precursor cation HP(CH3NCH2CH2)3N+ (2) to 1a, which is more stable and less expensive, is reported herein to be an efficient procatalyst for these reactions and also for the debromination of vicinal dibromides using Nail as a relatively inexpensive stoichiometric hydride source in CH3CN at room temperature. In dehydrohalogenations requiring more than ca. 10 h, the CH2CN- ion also acts as a base. By itself, Nail does not function well or at all under the same conditions. A catalytic cycle is proposed in which hydride deprotonates cation 2 liberating catalytic la. The cations HP(HNCH2CH2)3N+, (3) and HP[N(polymer)CH2CH2]N(CH2CH2NH)2+ (4) are also shown to function as procatalysts for the efficient dehydrohalogenation of RX and for the debrommation of vicinal dibromides. The preparation of the heterogeneous procatalyst 4(OTf) is also described.
- Liu, Xiaodong,Verkade, John G.
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p. 4840 - 4843
(2007/10/03)
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- Denomination of vic-dibromides with 1,5-dichalcogenacyclooctane induced by transannular chalcogen-chalcogen interaction: The first example of the vic-dibromide-alkene functional group interconversion by organic selenide
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Vicinal dibromoalkanes are debrominated to alkenes by treatment with 1,5-dichalcogenacyclooctane under neutral conditions induced by transannular interaction. The first example of dehalogenation by using an organoselenium compound is described.
- Takaguchi, Yutaka,Hosokawa, Akira,Yamada, Sachiko,Motoyoshiya, Jiro,Aoyama, Hiromu
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p. 3147 - 3149
(2007/10/03)
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- Reduction with Samarium(0). Debromination of vic-Dibromides to Alkenes
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Three electrons from Sm(0) to Sm(III) can be available during the title reduction which was achieved in 90-95percent yield with vic-dibromides such as trans-10,11-dibromodibenzosuberone, meso- and dl-1,2-dibromo-1,2-diphenylethane, ethyl 2,3-dibromo-3-phenylpropionate, 2,3-dibromo-3-phenylpropionic acid, and cholesterol dibromide.These reductions were accelerated with a catalytic amount of acid.
- Yanada, Reiko,Bessho, Kiyoshi,Yanada, Kazuo
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p. 1279 - 1282
(2007/10/02)
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- Flash Vacuum Pyrolysis of 5-Diazodibenzocycloheptene. Some Insights into Aromatic Carbene-Arylcarbene Rearrangement
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Flash vacuum pyrolysis of the title diazo compound gives 4H-cyclopentaphenanthrene, which is interpreted as indicating that dibenzocycloheptatrienylidene (13) undergoes the carbene-carbene rearrangement to generate 4-phenanthrylcarbene.The reactivities of 13 are compared with those of other benzoannulated cycloheptatrienylidenes and discussed in terms of the effect of the benzo ring to the activation energy for the rearrangement.
- Tomioka, Hideo,Kobayashi, Noriyuki
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p. 327 - 329
(2007/10/02)
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- Selenium-catalysed Debromination of vic-Dibromides to Alkenes with Cysteine or Glutathione
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Sodium selenite catalyses, under mild conditions, the reductive debromination of vic-dibromides to alkenes in the presence of thiols cysteine or glutathione.
- Yanada, Kazuo,Yanada, Reiko,Meguri, Haruo
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p. 730 - 732
(2007/10/02)
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- Synthesis of o-Substituted Phenols by Criegee Rearrangement of Benzylic Hydroperoxides
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9-Phenylthioxanthen-9-ol, 10,10-dimethyl-9-phenyl-9,10-dihydroanthracen-9-ol, and 9-arylfluoren-9-ols undergo Criegee-type rearrangements when treated with hydrogen peroxide and acid to generate substituted benzophenones from the first two substrates, and monoesters of biphenyl-2,2'-diol from the fluorenes via subsequent Bayer-Villiger oxidation of the intermediate 2'-aroylbiphenyl-2-ol. 5-Phenyl-10,11-dihydrodibenzocyclohepten-5-ol and its dehydroderivative gave the corresponding heptanone and heptenone on treatment with acid and hydrogen peroxide.Prolonged reaction of the 5-phenyldibenzohepten-5-ol afforded products arising from oxidation of the double bond.
- Taljaard, Benjamin,Goosen, Andre,McCleland, Cedric W.
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p. 931 - 934
(2007/10/02)
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- Transannular Hydride Shift versus Cyclocondensation in 5-(2-Biphenylyl)-10,11-dihydro-5H-dibenzocyclohepten-5-ol Derivatives
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The title compounds 1a-c, stable under thermal and basis conditions, undergo a solvent-assisted concerted hydride shift/deprotonation reaction to 5-(2-biphenylyl)-5H-dibenzocycloheptene (4) in weak acids such as acetic acid, acetic anhydride, phenol, and nitromethane.In strong acids like formic acid or trifluoroacetic acid cyclization to 10,11-dihydrospirocycloheptene-5,9'-fluorene> (3) occurs via the carbenium ion intermediate 5. - Key Words: Elimination/ Hydride shift/ Spirocyclization
- Hellwinkel, Dieter,Becker, Thomas
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p. 1595 - 1598
(2007/10/02)
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- Carbene Cation Radicals: The Kinetics of Their Formation from Diazoalkane Cation Radicals and Their Reactions
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The unimolecular decomposition reacions of trhree diazoalkane (diazodiphenylmethane and related compounds) cation radicals were studied in acetonitrile, methanol, and mixed solvent.Kinetic studies, using transient electrochemical methods, show that the reaction rates are insensitive to solvent, the presence of nucleophiles, and the nature and concentration of electrolytes.At temperatures above 300 K the competing second-order reactions, observed to minor extents at lower temperatures, were insignificant.Arrhenius activation energies were observed to be the order of 16 kcal/mol with entropies of activation close to zero.It is suggested that the rate-determining step in all cases is unimolecular loss of dinitrogen (reaction i) to generate the reactive carbene cation radicals.The carbene cation radicals show reaction patterns that exhibit both electrophilic and Ar2C=N2.+ -> Ar2C.++N2 radical-like facets.In acetonitrile complex reaction mixtures were obtained suggesting that the carbene cation radicals react rather indiscriminately.In more nucleophilic methanol, the major products were Ar2C(OMe)2, Ar2C=O, and Ar2CHOMe in proportions depending strongly on the structure of the carbene cation radical.
- Parker, Vernon D.,Bethell, Donald
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p. 5066 - 5072
(2007/10/02)
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- Ketene. Part 23. Conformational Control of the Addition Reactions of Ketenes with N-Phenylnitrones
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X-Ray analysis shows that the nitrone group in (5a) is not distorted, disproving a previous explanation for the formation of oxazolidinones rather than indolones in the reactions with ketenes.Nitrone (5c) reacts with dimethylketene and diphenylketene to form oxazolidinones (6c,d) whereas nitrones (5d) and (5e) under similar conditions form indolone derivatives (9).Oxazolidinone formation by the reaction of ketenes with nitrones (5a-c) results from restricted rotation about the N-phenyl bond preventing the -migration (3) -> (4), which precedes indolone formation.
- Falshaw, Christopher P.,Hashi, Nur A.,Taylor, Giles A.
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p. 1837 - 1844
(2007/10/02)
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- Dimethylboron Bromide and Diphenylboron Bromide: Cleavage of Acetals and Ketals
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The cleavage of various acetal and ketal derivatives by the use of dialkyl- and diarylboron halides is described.Acetals and ketals readily react with dimethylboron bromide or diphenylboron bromide at -78 deg C to give the corresponding carbonyl compounds in excellent yield.Under similar reaction conditions MEM, MOM, and MTM ethers are smoothly converted to alcohols.Acetonides are also cleaved with dimethylboron bromide while THP and THF ethers and methyl glycosides react at room temperature.Mechanistic considerations of the cleavage reactions are presented.The chemoselective virtues of dimethylboron bromide are summarized.
- Guindon, Yvan,Yoakim, Christiane,Morton, Howard E.
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p. 3912 - 3920
(2007/10/02)
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- DIMETHYLBORON BROMIDE AND DIPHENYLBORON BROMIDE. ACETAL AND KETAL CLEAVAGE. CLEAVAGE OF MEM, MOM AND MTM ETHERS.
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A general and efficient procedure for the cleavage of acetals and ketals by the use of dimethylboron bromide or diphenylboron bromide is described.Under similar reaction conditions, MEM, MOM and MTM ethers also react to afford the parent alcohols in excellent yields.
- Quindon, Yvan,Morton, Howard E.,Yoakim, Christiane
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p. 3969 - 3972
(2007/10/02)
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