- REACTIONS OF 1-OXA-3-AZONIABUTATRIENE SALTS WITH 1,3-DIPOLES
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The nitrile N-oxide 4 undergoes a reversible cycloaddition to the carbonyl group of the 1-oxa-3-azoniabutatriene salts 3a-c to give the geminal dioxy substituted 2-azoniaallene salts 5a-c.Azibenzil 7 and 3a,d afford the 2-azoniaallene salts 8a,d.With the nitrone 11 the cumulene 3d reacts to yield the open-chain addition product 12.The salt 3a reacts with two equivalents of diazofluorene to give the β-lactamium salt 13, which can be hydrolyzed to afford the N-formyl-β-lactam 15.X-ray structural analyses of 5b and 8d confirm the proposed constitutions.
- Hamed, Atef,MueLler, Edgar,Jochims, Johannes C.,Zsolnai, Laszlo,Huttner, Gottfried
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- Regioselectivity of the 1,3-dipolar cycloaddition of fluorinated fluoren-9-iminium ylides to heteroelement-containing dipolarophiles: Experimental and quantum-chemical study
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N-Substituted 9H-fluoren-9-imines react with difluorocarbene to give the corresponding iminium ylides whose further transformations in the absence of active dipolarophiles depend on the substituent at the nitrogen atom and reaction conditions. N-Ethyl-, N
- Novikov,Khlebnikov,Egarmin,Shevchenko,Khlebnikov,Kostikov,Vidovic
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- Structural influences impacting the role of the 9-ylidene bond in the electronic tuning of structures built upon 9-fluorenylidene scaffolds
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A structure-effect study is presented pertaining to the HOMO-LUMO tuning of compounds built upon the 9-fluorenylidene scaffold frequently incorporated as a moiety within organic-based semiconducting materials. The results represent the first reported analysis employing an ensemble of spectroscopy, electrochemistry, and crystal structure data to elucidate and compare the electronic properties of 9-fluorenones, 9-fluorenylidenes, and 9-fluorenimine derivatives. The results also provide the first spectroscopically and crystallographically measured description of exciton coupling within 9,9′-bifluorenylidenes. The 9-ylidene bond is seen to play a key role impacting the electronic properties, and an examination of the effects of substituents, conjugation, heteroatoms, and steric strain on the 9-ylidene bond in a diverse set of structures with representative structural variations relevant to the HOMO-LUMO tuning is presented. Increasing conjugation decreased the HOMO-LUMO gap (HLG), increased the HOMO energy (EHOMO), but decreased the LUMO energy (ELUMO). Substituent effects were observed to produce only slight changes that tended to decrease the HLG and increase both EHOMO and ELUMO, while heteroatom inclusion at the 9-ylidine bond tended to decrease the HLG, EHOMO, ELUMO, and the extinction coefficient. In the sterically hindered 9,9′- bifluorenylidenes, increased steric strain that promoted either an increase in the torsion angle or bond length of the 9-ylidene bond was seen to decrease the HLG via exciton coupling. These results elucidate the HOMO-LUMO tuning of systems containing a 9-fluorenylidene moiety and may assist in developing materials with specifically tuned HLGs and HOMO-LUMO levels for a variety of applications.
- Eakins, Galen L.,Cooper, Matthew W.,Gerasimchuk, Nikolay N.,Phillips, Terry J.,Breyfogle, Bryan E.,Stearman, Chad J.
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- 1,3-Dipolar cycloadditions, 97: Some cycloadditions of aromatic thione S-oxides
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Surprisingly, thiobenzophenone S-oxide (5) and thione 6 afforded the spiro-1,2,4-trithiolane 7 (86%) instead of the expected spiro-1,2,4-oxadithiolane 16. Structure 7 was established via spectra, single-crystal X-ray analysis, and an independent synthesis from thiobenzophenone S-sulfide (15) and 6. On accepting the formation of 16 by 1,3-cycloaddition as a first step, we reduced the mechanistic problem to the conversion 16 + 6 → 15 + dione 8; three conceivable pathways are discussed. Thiofluorenone S-oxide (25) combines with 6 to the trithiolane 27 in low yield; the spontaneous conversion of 25 to 9,9′-bifluorenylidene (26) takes precedence. No 1,3-cycloaddition is involved in the 1:1 reaction of 5 with (E)-cyclooctene (28); 5 combines as a hetero-1,3-diene with 28 to a Diels-Alder type adduct 30. VCH Verlagsgesellschaft mbH, 1997.
- Huisgen, Rolf,Mloston, Grzegorz,Polborn, Kurt,Palacios-Gambra, Francisco
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- The reaction of electrophilic terminal phosphinidene complexes with benzophenone and fluorenone: The unexpected formation of six- and eight-membered heterocycles
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The phenylphosphinidene-pentacarbonyltungsten complex 2, as generated from the appropriate 7-phosphanorbornadiene complex 1, reacts at 60°C with benzophenone to give a benzo-annellated 1-oxa-2-phosphacyclohex-4-ene 2-oxide as a 1:1 mixture of two isomers 3a,b. The same phosphinidene complex 2 reacts at 120°C with fluorenone. A deoxygenation of fluorenone takes place leading to the bifluorenylidene 4 and to an eight-membered 1,2,8-oxadiphosphocane 2,8-dioxide 5. Both compounds 3b and 8 have been fully characterized by X-ray crystal structure analysis. The two reactions are interpreted as resulting from the initial formation of a P ... O Lewis adduct between the phosphinidene and the ketone.
- Inubushi, Yoichi,Huy, Ngoc Hoa Tran,Ricard, Louis,Mathey, Francois
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- A Kinetic Study on Denitration of 9,9'-Dinitro-9,9'-bifluorenyl by Tin(II) Chloride in N,N-Dimethylformamide
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The kinetics of the reductive elimination of nitro groups from 9,9'-dinitro-9,9'-bifluorenyl by tin(II) chloride in N,N-dimethylformamide (DMF) at 20 deg C was investigated.It was found that the present elimination is a second-order reaction.
- Fukunaga, Kimitoshi,Kimura, Makoto
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- Trivalent organophosphorus reagent induced pinacol rearrangement of 4H-cyclopenta[2,1-b:3,4-b′]dithiophen-4-one
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In this Letter we report on the reaction of 4H-cyclopenta[2,1-b:3,4- b′]dithiophen-4-one with various trivalent organophosphorus derivatives, with an emphasis on the final products depending on the applied reagents. No reaction occurred upon treatment with either triphenyl- or tricyclohexylphosphine, whereas addition of triethyl phosphite or tri(n-butyl)phosphine resulted in pinacol rearrangement. Structure elucidation of the isolated 5H-spiro(benzo[1,2-b:6,5-b′]dithiophene-4,4′- cyclopenta[2,1-b:3,4-b′]dithiophen)-5-one was achieved by combined NMR experiments, theoretical chemical shift and geometry calculations, and single crystal X-ray analysis.
- Marin, Lidia,Zhang, Yuexing,Robeyns, Koen,Champagne, Beno?t,Adriaensens, Peter,Lutsen, Laurence,Vanderzande, Dirk,Bevk, David,Maes, Wouter
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- TRANSITION METAL PROMOTED REACTIONS XIV. NOVEL REDUCTIVE COUPLING OF THIOKETALS WITH MOLYBDENUM HEXACARBONYL
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Thioketals of fluorenone, acetophenone, tetralone and indanone were treated with Mo(CO)6 in chlorobenzene to give the corresponding dimeric olefins.
- Wong, Chi Sang,Leung, Wing Sang,Yeung, Lam Lung,Luh, Tien-Yau
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- Inclusion crystals of 2,2′,7,7′,9,9′-hexahalo-9,9′-bisfluorenyl derivatives: a new family of polyhalo aryl hosts
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The preparation and inclusion properties of the new halo aryl hosts, 2,2′,7,7′,9,9′-hexahalo-9,9′-bisfluorenyl derivatives 5-7, are described. The host compounds 5-7 having four halogen atoms on the aromatic rings form stable inclusion crystals with many guest compounds, whereas the parent compound 4 does not. The X-ray structures of the host 4 and representative inclusion compounds of hosts 5-7 were determined, allowing rationalization of several of the experimental observations.
- Tanaka, Koichi,Wada, Shin-ichi,Caira, Mino R.
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- (PNP)Cobalt-Catalyzed Olefination of Diazoalkanes
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Addition of excess diazoalkane to the pincer-supported cobalt(I) dinitrogen complex (tBumPNP)CoN2 (tBumPNP = modified 2,6-bis[(ditert-butylphosphino)methyl]pyridine) resulted in the catalytic formation of the homocoupled alkene product with concomitant loss of N2. Monosubstituted diazoalkanes, trimethylsilyldiazomethane and tolyldiazomethane, generated the olefin product in quantitative yield with exclusive (E)-stereoselectivity. Disubstituted diazoalkanes, diphenyldiazomethane and 9-diazofluorene, also yielded the olefin as the major product along with minor azine coupling. Investigations into the nature of the diazoalkane-cobalt interaction by multinuclear NMR spectroscopy and X-ray diffraction established end-on diazoalkane cobalt complexes as the resting states. The isolated four-coordinate cobalt diazoalkane complexes promoted conversion to the corresponding olefin. The reaction of (tBumPNP)CoN2 with an α-diazo-β-ketoester resulted in the formation of a five-coordinate Co(I)-diazoalkane complex with a chelating ester unit that was unreactive for olefination.
- Chirik, Paul J.,Semproni, Scott P.,Yruegas, Sam
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supporting information
(2022/03/17)
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- α-Bromoacrylic Acids as C1 Insertion Units for Palladium-Catalyzed Decarboxylative Synthesis of Diverse Dibenzofulvenes
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Herein α-bromoacrylic acids have been employed as C1 insertion units to achieve the palladium-catalyzed [4 + 1] annulation of 2-iodobiphenyls, which provides an efficient platform for the construction of diverse dibenzofulvenes. This protocol enables the formation of double C(aryl)-C(vinyl) bonds via a C(vinyl)-Br bond cleavage and decarboxylation. It is particularly noteworthy that the method features a broad substrate scope, and various interesting frameworks, such as bridged ring, fused (hetero)aromatic ring, and divinylbenzene, can be successfully incorporated into the products.
- Zhang, Minghao,Deng, Wenbo,Sun, Mingjie,Zhou, Liwei,Deng, Guobo,Liang, Yun,Yang, Yuan
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p. 5744 - 5749
(2021/08/18)
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- Direct Observation of Aggregation-Induced Emission Mechanism
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The mechanism of aggregation-induced emission, which overcomes the common aggregation-caused quenching problem in organic optoelectronics, is revealed by monitoring the real time structural evolution and dynamics of electronic excited state with frequency and polarization resolved ultrafast UV/IR spectroscopy and theoretical calculations. The formation of Woodward–Hoffmann cyclic intermediates upon ultraviolet excitation is observed in dilute solutions of tetraphenylethylene and its derivatives but not in their respective solid. The ultrafast cyclization provides an efficient nonradiative relaxation pathway through crossing a conical intersection. Without such a reaction mechanism, the electronic excitation is preserved in the molecular solids and the molecule fluoresces efficiently, aided by the very slow intermolecular charge and energy transfers due to the well separated molecular packing arrangement. The mechanisms can be general for tuning the properties of chromophores in different phases for various important applications.
- Corminboeuf, Clémence,Guan, Jianxin,Han, Han,Lin, Kun-Han,Liu, Jitian,Peng, Jie,Prlj, Antonio,Wei, Rong,Yu, Zhihao,Zhao, Dahui,Zheng, Junrong
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supporting information
p. 14903 - 14909
(2020/07/04)
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- Substituent Effects on Reactions of [RhCl(COD)]2 with Diazoalkanes
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The reactions of [RhCl(COD)]2 with a series of diazoalkanes with different substitutents were investigated. The outcomes of the reactions were found to be substituent-dependent via four different pathways. (1) The reactions with diazoindenes produced ??5-cyclopentadienyl complexes. (2) The reaction with diazofluorene produced a mixture of olefin and azine compounds. (3) The reactions with monosubstituted diazoalkanes RCHN2 (R = Ph, MeO2C) produced olefins RCHa?CHR. (4) The reaction with the disubstituted diazoalkane Ph2CN2 produced the azine Ph2Ca?N-Na?CPh2 only. Computational studies have been carried out to understand the interesting substituent effect by comparing the kinetics and thermodynamics of the reaction pathways. It was found that the reactions with diazocyclopentadiene, diazoindene, and Ph2CN2 are kinetically controlled, while the reactions with RCHN2 and diazofluorene are both thermodynamically and kinetically controlled.
- Cui, Mingxu,Lin, Shujuan,Sung, Herman H. Y.,Williams, Ian D.,Lin, Zhenyang,Jia, Guochen
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p. 905 - 915
(2019/03/04)
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- Synthesis and Structure of a Strained, Cyclic meta-Quaterphenylene Acetylene
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A strained, cyclic hydrocarbon comprising a meta-quaterphenyl-based arc that is clamped by an alkyne tether was synthesized via Yamamoto coupling of a dichloro precursor. DFT calculations (B3LYP/6-31G*) indicate that the lowest-energy ground state adopts
- De Hoe, Clement,Dean, Ryan T.,Hacker, Allison S.,Dutta, Sudeep H.,Dominguez, Omar,Parsons, Leo W. T.,Sommerville, Parker J. W.,Vandivier, Kai P.,Chalifoux, Wesley A.,Frantz, Derik K.
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p. 4522 - 4527
(2019/07/19)
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- Nickel-catalyzed synthesis of 9-monoalkylated fluorenes from 9-fluorenone hydrazone and alcohols
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A practical protocol was disclosed for the nickel-catalyzed C-alkylation of 9-fluorenone hydrazone with alcohols using t-BuOK as the base, and 9-monoalkylated fluorene derivatives were obtained in good yields under the benign conditions.
- Fan, Jiang-Tao,Fan, Xin-Heng,Chen, Yong-Jie,Gao, Cai-Yan,Yang, Lian-Ming
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p. 2895 - 2902
(2019/08/12)
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- Iron(III) nitrate-induced aerobic and catalytic oxidative cleavage of olefins
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Microwave-assisted catalytic oxidative cleavage of olefins using Fe(NO3)3·9H2O under O2 is reported. This reaction system is particularly effective when 9-benzylidene-9H-fluorene derivatives are used as substrates even though they are tri- and tetra-substituted olefins.
- Amaya, Toru,Fujimoto, Hayato
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p. 2657 - 2660
(2018/06/04)
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- A novel application of 2-silylated 1,3-dithiolanes for the synthesis of aryl/hetaryl-substituted ethenes and dibenzofulvenes
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Trimethylsilyldiazomethane (TMS-CHN2) reacts readily with hetaryl thioketones to give sterically crowded 2-trimethylsilyl- 4,4,5,5-tetrahetaryl-1,3-dithiolanes with complete regioselectivity at -75 °C as well as at rt. Thiofluorenone, a relatively stable and highly reactive aryl thioketone, yields upon treatment with TMS-CHN2at -60 °C the corresponding 1,3,4-thiadiazoline. This unstable cycloadduct undergoes decomposition at ca. -45 °C and the silylated thiocarbonyl S-methanide generated thereby is trapped with complete regioselectivity by aryl or hetaryl thioketones forming also sterically crowded 2-trimethylsilyl-1,3- dithiolanes. The obtained 1,3-dithiolanes, by treatment with an equimolar amount of TBAF in a one-pot procedure, are converted in high yields into hetaryl/aryl-substituted ethenes or dibenzofulvenes, respectively, via a cycloreversion reaction of the intermediate 1,3-dithiolane carbanion. The presented protocol offers a new, highly efficient approach to tetrasubstituted ethenes and dibenzofulvenes bearing aryl and/or hetaryl substituents.
- Mloston, Grzegorz,Pipiak, Paulina,Hamera-Fa?dyga, Róza,Heimgartner, Heinz
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p. 1900 - 1906
(2017/09/27)
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- Phase-vanishing method applied to condensation reactions using TiCl4
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The phase-vanishing (PV) method using perfluorohexanes as the phase screen was applied to the aldol condensation using TiCl4 as the Lewis acid. A special test tube was used, in which an interface between the fluorous and organic layers was stirred, and cyclohexanone was treated with two equivalents of benzaldehyde derivatives under PV conditions to afford corresponding 2,6-dibenzylidencyclohexanone in good yields. The formyl-methylenation of ketones with triethylamine using TiCl4 was also demonstrated by the PV method.
- Adachi, Yusuke,Kuniyoshi, Kenji,Matsubara, Hiroshi
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p. 100 - 105
(2017/04/10)
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- FULVENE DERIVATIVE AND METHOD FOR PRODUCING FULVENE DERIVATIVE
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PROBLEM TO BE SOLVED: To provide a fulvene derivative excellent in characteristics as a luminescent material and a method for producing a fulvene derivative which enables safer production of such a fulvene derivative. SOLUTION: There is provided a fulvene derivative represented by the following formula (1). In the formula, the dotted line arcs may be the same with or different from each other and represent that ring structures are formed together with portions of a five-membered skeleton part; X1 and X2 represent a hydrogen atom or a monovalent substituent which becomes a substituent of a ring structure, where a plurality of them may be bound to respective ring structures which constitute the dotted line arcs; Y1 and Y2 represent one of C, S, N, and O; and R1 and R2 represent atomic groups bound to Y1 and Y2, respectively, and R1 and R2 form a bond at least at one position. COPYRIGHT: (C)2015,JPOandINPIT
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Paragraph 0162; 0163
(2018/10/31)
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- Microwave flash pyrolysis: C9h8 interconversions and dimerisations
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The pyrolysis of 2-ethynyltoluene, indene, fluorene, and related compounds has been studied by sealed tube microwave flash pyrolysis (MFP), in concert with modelling of putative mechanistic pathways by density functional theory (DFT) computations. In the MFP technique, samples are admixed with graphite and subjected to intense microwave power (150-300 W) in a quartz reaction tube under a nitrogen atmosphere. The MFP reaction of 2-ethynyltoluene gave mostly indene, the product of a Roger Brown rearrangement (1,2-H shift to a vinylidene) followed by insertion. An additional product was chrysene, the likely result of hydrogen atom loss from indene followed by dimerisation. The intermediacy of dimeric bi-indene structures was supported by pyrolysis of bi-indene and by computational models. Benzo[a]anthracene and benzo[c]phenanthrene are minor products in these reactions. These are shown to arise from pyrolysis of chrysene under the same MFP conditions. MFP reaction of fluorene gave primarily bi-fluorene, bifluorenylidene, and dibenzochrysene, the latter derived from a known Stone-Wales rearrangement.
- Ajaz, Aida,Voukides, Alicia C.,Cahill, Katharine J.,Thamatam, Rajesh,Skraba-Joiner, Sarah L.,Johnson, Richard P.
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p. 1301 - 1308
(2014/11/07)
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- Reduction of thiocarbonyl compounds with lithium diisopropylamide
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Treatment of 4,4-disubstituted 2-phenyl-1,3-thiazole-5(4H)-thiones with lithium diisopropylamide (LDA; LiNiPr2) in THF at -78° yielded the corresponding 1,3-thiazole-5(4H)-thioles in moderate yields. Sequential treatment with LDA and
- Gebert, Andreas,Jasiński, Marcin,Mlostoń, Grzegorz,Heimgartner, Heinz
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p. 931 - 938
(2014/08/05)
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- Pd-catalyzed synthesis of 9,9-bifluorenylidene derivatives via dual C-H activation of bis-biaryl alkynes
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We report a novel Pd-catalyzed alkyne-directed dual C-H activation of bis-biaryl alkynes, which produced important and useful products, 9,9-bifluorenylidene (9,9BF) derivatives, in high yields with a broad range of functional group compatibility. The combination of the PdCl2 catalyst with the MnO2 oxidant and PivOH additive is vital for realization of the present catalytic transformation. Mechanistic evidence suggests that this intramolecular arene/alkyne annulation may take place through unusual dual C-H activation followed by annulation with alkynes.
- Zhao, Jian,Asao, Naoki,Yamamoto, Yoshinori,Jin, Tienan
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supporting information
p. 9540 - 9543
(2014/07/22)
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- High open circuit voltage organic photovoltaic cells fabricated using 9,9′-bifluorenylidene as a non-fullerene type electron acceptor
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We have found that 9,9′BF can be used as an electron acceptor for P3HT-based OPVs while similar devices using 4,4′BP do not show any photovoltaic effect. This can be related to the respective aromaticity and antiaromaticity of the reduced forms of 9,9′BF or 4,4′BP. The OPV device fabricated using P3HT and 9,9′BF exhibited a PCE of 2.28% with a Voc of 1.07 V, a Jsc of 5.04 mA cm-2, and a FF of 0.42. The Royal Society of Chemistry 2013.
- Kim, Hee Un,Kim, Ji-Hoon,Suh, Hongsuk,Kwak, Jeonghun,Kim, Dongwook,Grimsdale, Andrew C.,Yoon, Sung Cheol,Hwang, Do-Hoon
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supporting information
p. 10950 - 10952
(2013/11/19)
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- New synthesis of dibenzofulvenes by palladium-catalyzed double cross-coupling reactions
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Palladium-catalyzed double cross-coupling reactions of 1,1-bis(pinacolato) borylalk-1-enes with 2,2′-dibromobiaryls and of 9-stannafluorenes with 1,1-dibromoalk-1-enes have been demonstrated to serve as new synthetic methods for dibenzofulvenes.
- Shimizu, Masaki,Nagao, Ikuhiro,Kiyomoto, Shin-Ichi,Hiyama, Tamejiro
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p. 1277 - 1284,8
(2020/09/09)
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- On the dual role of N-heterocyclic carbenes as bases and nucleophiles in reactions with organic halides
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The synthetic consequences of different basicities, nucleophilicities, and sterics of N-heterocyclic carbenes have been studied in reactions of imidazolin-2-ylidenes with organic halides. Highly nucleophilic and less basic carbenes cleanly gave alkyli-deneimidazolines, the deoxy analogues of Breslow-type intermediates. More basic NHCs engaged in unwanted deprotonation or dehydrohalogenation reactions. Georg Thieme Verlag Stuttgart. New York.
- Knappke, Christiane E. I.,Arduengo, Anthony J.,Jiao, Haijun,Neudoerfl, Joerg-Martin,Jacobivonwangelin, Axel
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scheme or table
p. 3784 - 3795
(2012/01/11)
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- Peterson olefination: Unexpected rearrangement in the overcrowded polycyclic aromatic ene series
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An attempted synthesis of the angularly annelated 9-(11′-benzo[a] fluoren-11′-ylidene)-9H-fluorene (3) through a Peterson olefination reaction between (9H-fluoren-9-yl)trimethylsilyl anion (5a) and 11H-benzo[a]fluoren-11-one (6) led to the linearly annelated 9-(11′-benzo[b]fluoren-11′-ylidene)-9H-fluorene (4), due to an unexpected rearrangement. The proposed mechanism of the rearrangement is illustrated. The core of the mechanism is an intramolecular Haller-Bauer cleavage of the naphthyl C11a′-C11′ bond in the β-oxysilane anion 11 (formed from 5a and 6) to give the 1-naphthyl anion (E)-12, followed by E/Z isomerization to (Z)-12 and by proton migration to give the 3-naphthyl anion (Z)-14. The intramolecular nucleophilic addition of the naphthyl anion at C-3′ of (Z)-14 to the carbonyl carbon gives the β-oxysilane anion 15, a benzo[b]fluorenylidene derivative. The mechanism is supported by the results of DFT calculations. The synthesis of 3 was achieved by application of Barton's double extrusion diazo-thione coupling method.
- Assadi, Naela,Pogodin, Sergey,Agranat, Israel
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experimental part
p. 6773 - 6780
(2011/12/21)
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- Cyclopropanespiro-β-lactones derived from 4-[(Z)-ethylidene]-3- methyloxetan-2-one: Diastereoselective formation and rearrangement reactions
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The metal catalysed reaction of monosubstituted diazo esters and ketones with 4-[(Z)-ethylidene]-3-methyloxetan-2-one results in the formation of cyclopropanespiro-β-lactones. In contrast to most alkene cyclopropanations, including those involving diketene, the reaction occurs diastereoselectively. A computational model of the reaction has been developed that accounts for the observed stereochemistry. The metal promoted thermal rearrangement of these spiro compounds is also unusual in that it affords pyranones, rather than the decarboxylation products characteristic of β-lactones in general, or the furanones formed from diketene derived cyclopropanespiro-β-lactones.
- Geraghty, Niall W.A.,McArdle, Patrick,Mullen, Laverne M.A.
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experimental part
p. 3546 - 3552
(2011/06/11)
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- BIFLUORENYLIDENE DERIVATIVES, THEIR PREPARATION AND USES THEREOF
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The invention relates to bifluorenylidene derivatives and their corresponding radical anions and radical-cations of the following general formula (II): wherein: Y = C=O and m is an integer ≥0, preferably m = 1, with the proviso that when m = 0, A = borany
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Page/Page column 12
(2010/04/27)
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- Reactions of diazo compounds with alkenes catalysed by [RuCl(cod)(Cp)]: Effect of the substituents in the formation of cyclopropanation or metathesis products
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The reaction of diazo compounds with alkenes catalysed by complex [RuCl(COd)(Cp)] (cod = 1, 5-cyclooctadiene, Cp = cyclopentadienyl) has been studied. The catalytic cycle involves in the first step the decomposition of the diazo derivative to afford the reactive [RuCl(Cp)I=C(R1)R 2)] intermediate and a mechanism is proposed for this step based on a kinetic study of the simple coupling reaction of ethyl diazoacetate. The evolution of the Ru-carbene intermediate in the presence of alkenes depends on the nature of the substituents at both the diazo N2=C(R 1)R2 (R1, R2 = Ph, H; Ph, CO 2Me; Ph, Ph; C(R1)R2 = fluorene) and the olefin substrates R3(H)C= C(H)R4 (R3, R4 = CO2Et, CO2Et; Ph, Ph; Ph, Me; Ph, H; Me, Br; Me, CN; Ph, CN; H, CN; CN, CN). A remarkable reactivity of the complex was recorded, especially towards unstable aryldiazo compounds and electron-poor olefins. The results obtained indicate that either cyclopropanation or metathesis products can be formed: the first products are favoured by the presence of a cyano substituent at the double bond and the second ones by a phenyl.
- Basato, Marino,Tubaro, Cristina,Biffis, Andrea,Bonato, Marco,Buscemi, Gabriella,Lighezzolo, Filippo,Lunardi, Pamela,Yianini, Chiara,Benetollo, Franco,Del Zotto, Alessandro
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experimental part
p. 1516 - 1526
(2009/09/04)
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- Vanadium(I) chloride and lithium vanadium(I) dihydride as selective epimetallating reagents for π- and σ-bonded organic substrates
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Subvalent vanadium(I) salts, of empirical formulas, VCl, vanadium(I) chloride and LiVH2, lithium vanadium(I) dihydride, whose efficient preparation, structural constitution and mode of reaction toward certain organic substrates have been described in a preceding article, are here evaluated in their reactions toward a wide variety of π- and σ-bonded organic substrates, namely carbonyl, imine, azo, alkene, 1,3-diene, nitrile π-bonds and C-X, C-O, C-N and N-N σ-bonds. Compared with the high reactivity of CrCl and LiCrH2 reagents in attacking both types of bonds, the VCl and LiVH2 reagents were much milder and selective in epimetallating π-bonds, often forming the 1:1 adduct of LiVH2 and π-bonded substrate as the major product. Finally, the vanadium reagents showed little tendency to cleave C-O, C-S and C-N bonds and a smaller scope in cleaving C-X bonds than their chromium counterparts. Because of their selectivity these vanadium reagents offer the following preparative promise: 1) smooth McMurry carbonyl coupling to their reductive dimers; 2) deoxygenation of epoxides; 3) selective aromatic C-X reduction; 4) high yields of epimetallated carbonyls or imines as intermediates to α-hydroxy and α-amino acids; 5) 1,4-reductions of 1,3-alkadienes; 6) reductive dimerization of nitriles to ketones; 7) 1,4 or 1,n-epimetallations leading to acyloins or indoles; and 8) reductive dimerizations of azines to produce unusual imidazole derivatives. In explaining the greater kinetic stability of the 1:1 LiVH2 adduct with carbonyl or imine substrates it is pointed out that such epimetallated adducts from LiVH2 would likely be diamagnetic, whereas such adducts from LiCrH2 have an unpaired electron on the Cr center and hence would rupture, so that the electron would be on the C center. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Eisch, John J.,Fregene, Paul O.
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scheme or table
p. 4482 - 4492
(2009/05/07)
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- Vanadium(I) chloride and lithium vanadium(I) dihydride as epimetallating reagents for unsaturated organic substrates: Constitution and mode of reaction
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Subvalent vanadium(I) salts, of empirical formulas, VCl, vanadium(I) chloride and LiVH2, lithium vanadium(I) dihydride, can be conveniently prepared in THF solution, starting at -78 °C, by treating either VCl3 or VCl4 with an appropriate number of equivalents of nBuLi. As judged by the stability of solutions or solid samples of LiVH2, the preparation of LiVH2 from VCl4 is the preferred method. Individual physical characterization of solid samples of VCl or of LiVH2, admixed with their LiCl by-product, was carried out after removal of all volatiles in vacuo and by the following measurements: 1) gasometric protolysis with glacial acetic acid and measurement of the H 2 evolved in the oxidation of VI to VII; 2) infrared spectroscopic search for V-H bands; and 3) examination for unpaired electrons by EPR activity. Such measurements applied to VCl lend strong support for a VI oxidation state but only probable evidence for paramagnetism and for the association of VCl units. Similar measurements applied to LiVH 2 give unambiguous gasometric and IR evidence favoring the LiVH 2 stoichiometry and the biradical nature of the VH2 anion with a linear array of H-V-H atoms. Chemical characterization of both VCl and LiVH2 toward individual organic substrates, such as olefins, ketones, epoxides and organic halides, yielded convincing evidence that organic radical mechanisms are involved, both for the proven biradical, LiVH2, as well as for the diamagnetic VCl. Finally, the question of why LiVH2 prepared from VCl4 is more stable than the LiVH2 obtained from VCl3 is addressed in terms of the actual coordination sphere of the VH2 anion in THF solution and in the solid state. Preliminary studies comparing the reactivities of LiVH2 and LiCrH2 toward organic substrates indicate that LiVH2 is the distinctly more moderate and usefully selective reductant. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Eisch, John J.,Fregene, Paul O.,Doetschman, David C.
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experimental part
p. 2825 - 2835
(2009/04/07)
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- Novel synthetic approach in microwave-assisted solid-supported oxidations using 'in situ' generated molecular oxygen
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Three different types of oxidation reactions were carried out under microwave (MW) conditions in dry media, with nearly quantitative yield, using 'in situ', yet separately generated molecular oxygen as the reactive gas. The latter is formed by a controlled decomposition of potassium chlorate (220-306 °C) adsorbed on zeolite support, and is used as a reactive oxidizing agent for the solid-supported oxidations. The MW-assisted oxidations include an oxidative decomplexation of (η6-arene)Cr(CO)3 complexes to the corresponding arenes using silica as solid support (100 °C), an oxidation of fluorene to fluorenone induced by KF-alumina support (150 °C), and oxidation of benzyl alcohol to benzaldehyde using a supported ruthenium catalyst (150 °C). This synthetic approach allows to carry out in synchronized manner two different solid-supported reactions (oxygen generation and oxidation) at different temperatures and on different solid supports together in the same sealed system. It was made possible by tuning the absorption efficiency of MWs through accurate selection of the solid supports employed in the reactions. The high feasibility of this novel synthetic approach resulted from a preliminary study of the interaction between MWs and mineral oxides such as alumina, silica, clay, and zeolite particularly when mixed with additives such as water, ionic liquids or graphite (5% w/w). The use of these MW absorber additives allows the MW transparent or poorly absorbing mineral oxides to be efficiently heated to very high temperatures in few minutes.
- Gershonov, Eytan,Katz, Esther,Karton, Yishai,Zafrani, Yossi
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p. 3762 - 3767
(2008/02/01)
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- Stereoselective synthesis of olefins by a reductive coupling reaction
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Ketones and aldehydes are converted to symmetrical and (E)-olefins (1-15) by reaction with 2,4-bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide (PhPSe2)2, Woollins' reagent, in refluxing toluene; use of diketones was demonstrated by the reaction of PhC(O)CH2C(O)Ph which gives 1,2,4,5-tetraphenylbenzene (16) in 83% yield. The Royal Society of Chemistry 2007.
- Hua, Guoxiong,Li, Yang,Slawin, Alexandra M. Z.,Woollins, J. Derek
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p. 1477 - 1480
(2007/10/03)
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- Different Z/E-selectivity depending upon the length of the acyl side chain in the formation of 2,2′-diacyl-9,9′-bifluorenylidene
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We studied the formation of 2,2′-diacyl-9,9′-bifluorenylidene from 2-acyl-9-bromofluorene via the corresponding intermediate 9-bromo-9,9′-bifluorenyl. It was found that dehydrobromination of the 9-bromo-9,9′-bifluorenyl derivatives occurred through the E2 elimination sequence, suggesting that the configuration of 9-bromo-9,9′-bifluorenyl isomers determined the stereochemistry of the product. Facile isomerization of the formed 9,90-bifluorenylidenes may give the observed stereo-selectivity depending upon the length of the acyl side chain.
- Oota, Atsushi,Imai, Toshinobu,Yamazaki, Ayumi,Oba, Toru,Karikomi, Michinori,Minabe, Masahiro
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p. 333 - 335
(2007/10/03)
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- Highly regio- and diastereoselective chromium(0)-catalysed cyclopropanation of 1-alkoxy-1,3-dienes with diazo compounds
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Pentacarbonyl(η2-cis-cyclooctene)chromium(0) (1) is an efficient catalyst for diazo decomposition and selective [2+1]-cycloaddition reactions of the resulting carbene intermediates with electron-rich dienes. The cyclopropanation of 1-alkoxy-1,3
- Hahn, Norbert D.,Nieger, Martin,Doetz, Karl Heinz
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p. 1049 - 1056
(2007/10/03)
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- Microwave-assisted coupling of carbonyl compound: An efficient synthesis of olefin
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Self-coupling of various ketones and aldehyde as well as mixed coupling of ketones employing TiCl4/Zn under microwave irradiation has been carried out to afford the corresponding olefins.
- Ramana,Singh,Parihar
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p. 760 - 761
(2007/10/03)
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- Catalytic olefination of carbonyl compounds. Effect of the structure of the carbonyl compound on the reaction
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The mechanism of the novel reaction of catalytic olefination of carbonyl compounds was studied. The reaction involves the transformation of hydrazones of aromatic aldehydes and ketones into the corresponding dichloroalkenes and symmetrical azines by the treatment with carbon tetrachloride in the presence of CuCl as a catalyst. The stability of intermediate diazoalkanes is the main factor determining the direction of the reaction. In the case of sufficiently stable diazoalkanes, other products can be formed under the reaction conditions along with the products of catalytic olefination.
- Korotchenko,Shastin,Nenaidenko,Balenkova
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p. 492 - 497
(2007/10/03)
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- The Gomberg-type dimerization of bifluorenylidene radicals: An X-ray crystallographic investigation
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The reaction of phenylethynyllithium with 9-bromofluorene yields 9,9′-bifluorenylidene, 8, 9,9′-bifluorenyl, 9, and a molecule 10, of formula C52H32, in which coupling has occurred between a 9,9′-bifluorenyl fragment and a 9,9′-bifluorenylidene moiety such that a C(9) position of the former is attached to a C(3) site of the latter. This parallels the unsymmetrical radical coupling of triphenylmethyl radicals, which leads to the Gomberg dimer, rather than hexaphenylethane. The structure of 10 has been elucidated by X-ray crystallography, and a mechanistic rationale is offered.
- Harrington, Laura E.,Britten, James F.,McGlinchey, Michael J.
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p. 8057 - 8060
(2007/10/03)
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- Oxidation of C-H bonds by [(bpy)2(py)RuIVO] 2+ occurs by hydrogen atom abstraction
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Anaerobic oxidations of 9,10-dihydroanthracene (DHA), xanthene, and fluorene by [(bpy)2(py)RuIVO]2+ in acetonitrile solution give mixtures of products including oxygenated and non-oxygenated compounds. The products include those formed by organic radical dimerization, such as 9,9′-bixanthene, as well as by oxygen-atom transfer (e.g., xanthone). The kinetics of these reactions have been measured. The kinetic isotope effect for oxidation of DHA vs DHA-d4 gives k H/kD ≥ 35 ± 1. The data indicate a mechanism of initial hydrogen-atom abstraction forming radicals that dimerize, disproportionate and are trapped by the oxidant. This mechanism also appears to apply to the oxidations of toluene, ethylbenzene, cumene, indene, and cyclohexene. The rate constants for H-atom abstraction from these substrates correlate well with the strength of the C-H bond that is cleaved. Rate constants for abstraction from DHA and toluene also correlate with those for oxygen radicals and other oxidants. The rate constant for H-atom transfer from toluene to [(bpy)2(py)RuIVO]2+ appears to be close to that predicted by the Marcus cross relation, using a tentative rate constant for hydrogen atom self-exchange between [(bpy)2(py)Ru IIIOH]2+ and [(bpy)2(py)RuIVO] 2+.
- Bryant, Jasmine R.,Mayer, James M.
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p. 10351 - 10361
(2007/10/03)
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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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- Studies on reactions of thioketones with trimethyl(trifluoromethyl)silane catalyzed by fluoride ions
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Treatment of 2,2,4,4-tetramethylcyclobutane-1,3-dione (6) in THF with CF3SiMe3 in the presence of tetrabutylammonium fluoride (TBAF) yielded the corresponding 3-(trifluoromethyl)-3-[(trimethylsilyl)oxy]cyclobutanone 7 (Scheme 1) via nucleophilic addition of a CF3- anion at the C=O group and subsequent silylation of the alcoholate. Under similar conditions, the 'monothione' 1 reacted to give thietane derivative 8 (Scheme 2), whereas in the case of 'dithione' 2 only the dispirodithietane 9, the dimer of 2, was formed (Scheme 3). A conceivable mechanism for the formation of 8 is the ring opening of the primarily formed CF3 adduct A followed by ring closure via the S-atom (Scheme 2). In the case of thiobenzophenones 4, complex mixtures of products were obtained including diarylmethyl trifluoromethyl sulfide 10 and 1,1-diaryl-2,2-difluoroethene 11 (Scheme 4). Obviously, competing thiophilic and carbophilic addition of the CF3- anion took place. The reaction with 9H-fluorene-9-thione (5) yielded only 9,9′-bifluorenylidene (14; Scheme 6); this product was also formed when 5 was treated with TBAF alone. Treatment of 4a with TBAF in THF gave dibenzhydryl disulfide (15; Scheme 7), whereas, under similar conditions, 1 yielded the 3-oxopentanedithioate 17 (Scheme 9). The reaction of dithione 2 with TBAF led to the isomeric dithiolactone 16 (Scheme 8), and 3 was transformed into 1,2,4-trithiolane 18 (Scheme 10).
- Mloston, Grzegorz,Prakash, G. K. Surya,Olah, George A.,Heimgartner, Heinz
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p. 1644 - 1658
(2007/10/03)
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- Catalytic transformations of diazo compounds promoted by platinum(0) and dicationic platinum(II) complexes
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9-Diazofluorene (DAF) is decomposed either stoichiometrically or catalytically in the presence of the platinum(0) complex [Pt(C2H4)(PPh3)2] to give difluoren-9-ylidene-hydrazine in high yield. Under analogous reaction conditions, diphenyldiazomethane gives mostly the azine, Ph2CNNCPh2, while ethyl diazoacetate (EDA) affords, in low yield, a mixture of diethyl fumarate and maleate in approximately 10:1 molar ratio. The cyclopropanation of styrene with EDA is catalyzed by a series of dicationic complexes of the type [PtL2(NCCH3)2][Y]2 (L2=2PPh3, Ph2PCH=CHPPh2, Ph2PCH2CH2PPh2; Y=BF4, CF3SO3) in 1,2-dichloroethane at 60 °C for 24 h. DAF and EDA undergo insertion reactions into the OH bond of alcohols ROH (R=Me, Et, t-Bu, CH2CHCH2, Ph) at 25 °C in CH2Cl2-ROH (DAF or EDA-ROH molar ratio 1/20) in the presence of 1% mol of several dicationic platinum(II) complexes to give the corresponding ethers in excellent yields.
- Bertani, Roberta,Biasiolo, Monica,Darini, Katia,Michelin, Rino A,Mozzon, Mirto,Visentin, Fabiano,Zanotto, Livio
-
-
- Dispiro[fluorene-9,5′-[1,2,3,4]tetrathiane-6′, 9″-fluorene]
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The tetrathiane ring of the title compound, C26H16S4, has a chair conformation and the molecule has approximate C2 symmetry. Each of the two fluorene ring systems is virtually planar, with the ring planes intersecting at an angle of 67.58 (5)°. This novel compound has been formed as a side product from the treatment of 9H-fluorene-9-thione with methyl N-[(benzylidene)phenyl]glycinate in the presence of LiBr and 1,6-diazabicyclo[5.4.0]undecane.
- Linden,Gebert,Heimgartner
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p. 764 - 766
(2007/10/03)
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- Solvolytic stereoselective debromination of vic-dibromides with HMPA
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A simple and efficient procedure for the debromination of vic-dibromides has been reported with hexamethylphosphoric triamide at 155-160°C under a nitrogen atmosphere without the aid of any reagent.
- Khurana,Bansal,Chauhan
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p. 1089 - 1091
(2007/10/03)
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- Ozonation of 1,1,2,2-tetraphenylethene revisited: Evidence for electron- transfer oxygenations
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Ozonolyses of 1,1,2,2-tetraphenylethene (TPE, 1) have been described many times in the literature, but the reports are contradictory. This reaction is particularly important for understanding the mechanism of alkene ozonolysis, in view of possible stabilization of reactive intermediates by aryl groups. Thus, systematic investigations of ozonolysis in both aprotic solvents and in protic solvents are reported here. Attention is directed to the following details that have been underestimated in the past: i) the actual electronic structure of ground-state ozone (O3), ii) differentiation between strained and unstrained alkenes, iii) the significance of both the O3 concentration and the TPE concentration, iv) the influence of various solvents, including pyridine, v) the influence of the reaction temperature, vi) the role of electron-transfer catalysis (ETC) and, yii) the effect of structural modifications. Our results suggest that ozonolysis of TPE (1) does not include a 1,3-dipolar reaction step, but represents a particularly interesting example of electron-donor (TPE)/electron-acceptor (O3) redox chemistry. The present investigations include several crucial results. First, pure 3,3,6,6-tetraphenyltetroxane (3, m.p. 221°(dec.)) and pure tetraphenylethylene ozonide (4, m.p. 153°(dec.)) are prepared for the first time, although 3 and 4 have long been known. Second, the singlet diradical character of O3, lessened by means of hypervalent-electron interaction and predicted by different calculations, is evidenced via reaction with the spintrap galvinoxyl (2,6-bis(1-1-dimethylethyl)-4-{[3,5-bis(1,1- dimethylethyl)-4-oxocyclohexa-2,5-dien-1-ylidene]methyl}phenoxy; 8), and the zwitterionic reaction behavior of ground-state O3 is ruled out. Third, the electronacceptor ability of O3 is evidenced by reactions with suitable tetraaryl ethylenes: it is enhanced by addition of catalytic amounts of protons or Lewis acids. Fourth, the observed distribution of the O3 O-atoms to the two different olefinic C-atoms of the unsymmetric alkene 27b is in full agreement with an initial single-electron transfer (SET) step, followed by a radical mono-oxygenation to cause the crucial C,C cleavage. Final dioxygenation should lead to the generally known products (ozonides, tetroxanes, hydroperoxides). The regioselectivity is found to be inconsistent with the expected decay of an intermediate primary ozonide. Finally, the treatment of 1,2-bis(4-methoxyphenyl)acenaphthylene (36) with O3 (simultaneous transfer of three O-atoms) leads to the same experimental result as a stepwise transfer of one O-atom followed by a transfer of two O- atoms.
- Schank, Kurt,Beck, Horst,Buschlinger, Michael,Eder, Joerg,Heisel, Thomas,Pistorius, Susanne,Wagner, Christiane
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p. 801 - 826
(2007/10/03)
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- Lewis acid catalyzed reactions of thioketones with 1,2-epoxycyclohexane and 1,2-epoxycyclopentane
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Non-enolizable thioketones and 1,2-epoxycyeloalkanes undergo a Lewis acid catalyzed addition reaction to give 1,3-oxathiolanes. Appropriate reaction conditions are CH2Cl2 as the solvent BF3. Et2O as the Lewis acid, and a temperature between -78°and r.t. Under the reaction conditions, the 1,3-oxathiolanes are only moderately stable. They decompose to yield the corresponding epithiocycloalkane and ketone. In general, 1,3-dithiolanes are isolated as minor products or, after prolonged reaction, as the main product. These secondary products are formed via the Lewis acid catalyzed reaction of the intermediate epithiocycloalkane and a second molecule of the thioketone. In the reaction of thiobenzophenone and 1,2-epoxycyclohexane, trans-8,8- diphenyl-7,9-dioxabicyclo[4.3.0]nonane is formed in small amounts as an additional side product (Scheme 12). In all cases, the newly formed heterocycle and the carbocycle are trans-fused. This result is consistent with a nucleophilic ring-opening of the complexed oxirane by the thioketone via inversion of the configuration and subsequent formation of the O(1)-C(2) bond of the 1,3-oxathiolane (Scheme 13). The surprising formation of the fused 1,4-oxathiepan derivative 23 (Scheme 9) is in accordance with an ionic reaction mechanism (cf. Scheme 15).
- Blagoev, Milen,Linden, Anthony,Heimgartner, Heinz
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p. 2316 - 2335
(2007/10/03)
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- A variation of titanium-induced carbonyl coupling - Synthesis and conformations of terfluorenyl
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Reaction of fluorenone (4) with a low-valent titanium reagent generated from TiCl4 and Zn in THF in the presence of pyridine gave terfluorenyl (6) in 71% yield, bifluorenylidene (2), the conventional McMurry reaction product, in 2% yield, and additional reduction products. The reductive 'trimerization' was rationalized in terms of an attack of the intermediate fluorenone dianion on bifluorenylidene. The molecular structure of a single crystal of 6 indicated an approximately C2 conformation, with a slightly twisted central ring, and two equally folded side moieties with dihedral angles of 58.1°and 58.0°between the central and side five-membered rings. The AM1 and PM3 calculations showed C2 global minima, similar to the conformation in the crystal. The calculated C(s) transition state conformations were found to be 21.3 (AM1) and 19.9 (PM3) kcal/mol higher in energy than the global C2 minima. A 2D-NMR NOESY experiment on 6 supported the C2 (+sc,+sc) or C2 (-sc,-sc) conformation in solution.
- Pogodin, Sergey,Cohen, Shmuel,Agranat, Israel
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p. 1979 - 1984
(2007/10/03)
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- New desulfurdimerization of dithioketals induced by a 2,2'-bipyridine ligated nickel(0) complex
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Desulfurdimerization of various aromatic dithioketals is efficiently induced by a 2,2'-bipyridine ligated nickel(0) complex under mild conditions.
- Lourak, Moushine,Becker, Sandrine,Fort, Yves,Caubere, Paul
-
-
- Reductive coupling of aromatic aldehydes and imines by the low valent titanium species generated in the reaction of TiCl4 with Et3N
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Aromatic aldehydes and imines are converted to the corresponding diols and diamines using the low valent titanium species generated by the reaction of TiCl4 with triethylamine.
- Periasamy, Mariappan,Srinivas, Gadthula,Karunakar, Galla V.,Bharathi, Pandi
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p. 7577 - 7580
(2007/10/03)
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- Chromium complex catalyzed synthesis of spirocyclopropanes from diaryl diazo compounds - Direct NMR-spectroscopic observation of a carbene complex intermediate
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The [2 + 1] cycloaddition reaction of electron-rich alkenes such as enol ethers with 9-diazo-9H-fluorene (1) is efficiently catalyzed by pentacarbonyl(η2-cis-cyclooctene)chromium(0) (2). This cyclopropanation reaction shows a pronounced prefere
- Pfeiffer, Juergen,Nieger, Martin,Doetz, Karl Heinz
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p. 1011 - 1022
(2007/10/03)
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- Tetracyclic arenes by benzannulation of tricyclic carbene complexes of chromium with alkynes: Chemo-, regio-, and stereoselectivity
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The tricarbonyl chromium complexes 7-9 and the tetracyclic arenes 11-13 were synthesized from 1-hexyne and the tricyclic chromium carbene complexes 3-5, which are derived from diazo precursors. The nonplanar dibenzocycloheptenylidene complex 4 afforded the benzannulation product S(p)M(h)/R(p)P(h)-8 stereoselectively, as established by NMR spectra and an X-ray crystal structure analysis. The benzannulation failed with the carbene complexes 1 and 2, presumably due to their reduced propensity for decarbonylation. Upon reaction with 1-hexyne, carbene complex 21, bearing two electronically different arene substituents, revealed only a low regioselectivity (1.6:1) in favour of chromium complex 22, which results from the annulation of the less electron-rich arene ring.
- Pfeiffer, Juergen,Nieger, Martin,Doetz, Karl Heinz
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p. 1843 - 1857
(2007/10/03)
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- Diinsertion of fluorenylidene into a Sulfur-Sulfur bond of diaryl disulfides
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Upon irradiation (>340 nm) of a benzene solution of diazofluorene with di-p-tolyl- or di-p-anisyl disulfide, the corresponding 9,9'-bis(arylmercapto)bifluorenyl was afforded in moderate to good yield accompanied by formation of 9,9'-bis(arylmercapto)fluorene. The major reaction pathway is considered to be a disulfur ylide formation followed by two times of successive Stevens rearrangement or by concerted electron redistribution via [2,3]sigmatropic rearrangement.
- Kawamura, Yasuhiko,Akitomo, Kohji,Oe, Masaaki,Horie, Tokunaru,Tsukayama, Masao
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p. 8989 - 8992
(2007/10/03)
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- Organometallic chemistry sans organometallic reagents: Modulated electron-transfer reactions of sub valent early transition metal salts
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The potential of low-valent, early transition-metal reagents as selective reductants in organic chemistry has been foreshadowed by intensive research on the ill-defined and heterogeneous subvalent titanium intermediates generated in the McMurry reaction and its numerous variants. As part of a long-term research effort to develop soluble, well-defined transition-metal reductants of modulated and selective activity toward organic substrates, the THF-soluble reductant, titanium dichloride, has been thoroughly examined, as well as the analogous ZrCl2 and HfCl2 reagents, all of which are readily obtainable by the alkylative reduction of the Group 4 tetrachloride by butyllithium in THF. Noteworthy is that such interactions of MCl4, with butyllithium in hydrocarbon media lead, in contrast, to M(III) or M(IV) halide hydrides. Analogous alkylative reductions in THF applied to VCl4, CrCl3, and MoCl5 have yielded reducing agents similar to those obtained from MCl4 but gradated in their reactivity. Such reductants have proved capable of coupling carbonyl derivatives, benzylic halides, acetylenes and certain olefins in a manner consistent with an oxidative addition involving a two-electron transfer (TET). Such a reaction pathway is consistent with the observed stereochemistry for pinacol formation from ketones and for the reductive dimerization of alkynes. In contrast to the reaction of CrCl3 with two equivalents of butyllithium, which leads to a CrCl intermediate, the interaction of CrCl3 in THF with four equivalents of butyllithium at -78°C yields a reagent of the empirical formulation, LiCrH4 · 2 LiCl · 2 THF, as supported by elemental and gasometric analysis of its protolysis. This hydridic reductant cleaves a wide gamut of o carbon-heteroatom bonds (C-X, C-O, C-S and C-N), towards which the CrCl reductant is unreactive. The type of cleavage and/or coupled products resulting from the action of "LiCrH4" on these substrates is best understood as arising from single-electron transfer (SET). In light of the aforementioned findings, the gradated reducing action noted among TiCl2, ZrCl2, HfCl2 and CrCl, as well as the contrasting reducing behavior between CrCl and LiCrH4, there is no doubt that future research with early transition metals will continue to yield novel reductants of modulated and site-selective reactivity. VCH Verlagsgesellschaft mbH,.
- Eisch, John J.,Shi, Xian,Alila, Joseph R.,Thiele, Sven
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p. 1175 - 1187
(2007/10/03)
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