- Synthesis of 9-alkylidene-9H-fluorenes by a novel, palladium-catalyzed cascade reaction of aryl halides and 1-aryl-1-alkynes
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In the presence of a palladium catalyst and NaOAc, aryl iodides react with 1-aryl-1-alkynes to afford 9-alkylidene-9H-fluorenes in good yields. The products from this reaction are highly dependent on the base employed. This process appears to involve (1)
- Larock,Tian
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Read Online
- Design and synthesis of extended π-systems: Monomers, oligomers, polymers
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The synthesis of unconventional extended π-systems is described in an attempt to tailor the structures of organic compounds for specific optical and electrical properties. In order to emphasize the role of the π-conjugation and to correlate chemical structure and physical function both one-dimensional arylenevinylenes and two-dimensional ribbon-type molecules are considered. In the synthesis of the former the aryl-olefin coupling according to Heck is of special value, the synthesis of the latter is achieved by repetitive Diels-Alder cycloadditions and by two-step processes in which carefully designed polyaryl precursors are subjected to ring closure. Key ingredients of the present approach are the interplay of synthetic organic chemistry and synthetic macromolecular chemistry and the needs outlined by materials sciences. Thereby, transition from monomers to oligomers and polymers defines new requirements for the selectivity of the synthetic reactions and the tractability of the products.
- Scherf,Mullen
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Read Online
- Pd-Catalyzed Coupling of N-Tosylhydrazones with Benzylic Phosphates: Toward the Synthesis of Di- or Tri-Substituted Alkenes
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This study shows that various di- and tri-substituted alkenes with high chemoselectivity were obtained in good to high yields by coupling N-tosylhydrazones (NTHs) with benzylic phosphates as electrophilic partners. The obtained new catalytic system consis
- Zhang, Kena,Provot, Olivier,Alami, Mouad,Tran, Christine,Hamze, Abdallah
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p. 1249 - 1261
(2022/02/07)
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- An N-heterocyclic carbene-catalyzed switchable reaction of 9-(trimethylsilyl)fluorene and aldehydes: Chemoselective synthesis of dibenzofulvenes and fluorenyl alcohols
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An N-heterocyclic carbene-catalyzed synthesis of dibenzofulvenes and fluorenyl alcohols was developed. In the presence of 10 mol% NHC (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and 4 ? molecular sieves, 9-(trimethylsilyl)fluorene undergoes an olef
- Ma, Yu-Chuan,Luo, Jin-Yun,Zhang, Shi-Chu,Lu, Shu-Hui,Du, Guang-Fen,He, Lin
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supporting information
p. 3717 - 3721
(2021/05/04)
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- Manganese catalyzed switchableC-alkylation/alkenylation of fluorenes and indene with alcohols
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The usage of earth-abundant, nontoxic transition metals in place of rare noble metals is a central goal in catalysis. This would be especially interesting when the reactivity and selectivity patterns can be tuned. Herein, we introduced the first Mn-catalyzed selectiveC-alkylation and olefination of fluorene, and indene with alcohols. Various substrates including benzylic, heteroaromatic, and aliphatic primary and secondary alcohols are employed as alkylating agents. Mechanistic investigations and a kinetic study underpin the involvement of the olefinated intermediate to furnish the alkylated product.
- Mondal, Avijit,Pal, Debjyoti,Sharma, Rahul,Srimani, Dipankar
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supporting information
p. 10363 - 10366
(2021/10/12)
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- Palladium-catalyzed coupling reaction of 2-iodobiphenyls with alkenyl bromides for the construction of 9-(diorganomethylidene)fluorenes
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An atom economical protocol for the construction of 9-(diorganomethylidene)fluorenes through palladium-catalyzed coupling reactions of 2-iodobiphenyls with alkenyl bromides has been reported. The reaction proceeds through the C-H activation/oxidative addition/reduction elimination/intramolecular Heck coupling reaction to afford a series of 9-(diorganomethylidene)fluorenes with good yields. Control experiments demonstrate that a five-membered palladacycle acts as a key intermediate and β-H elimination serves as the rate-limiting step.
- Zhao, Ya-Heng,Wang, Jian-Long,Zhou, Yun-Bing,Liu, Miao-Chang,Wu, Hua-Yue
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supporting information
p. 8250 - 8253
(2021/10/12)
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- Synthesis of 9-Fluorenylidenes via Pd-Catalyzed C-H Vinylation with Vinyl Bromides
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A facile and efficient approach for the synthesis of 9-fluorenylidenes has been developed via the palladium-catalyzed cross-coupling of 2-iodobiphenyls and vinyl bromides. The reaction involves the C-H activation of 2-iodobiphenyls and dual C-C bond formations. A range of 9-fluorenylidene derivatives, including diphenyldibenzofulvenes, can be synthesized with the reaction.
- Yang, Shuai,Zhang, Yanghui
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supporting information
p. 7746 - 7750
(2021/10/12)
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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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- Intermolecular oxidative Friedel-Crafts reaction triggered ring expansion affording 9,10-diarylphenanthrenes
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A novel intermolecular tandem oxidative aromatic coupling between arylidene fluorenes and unfunctionalized aromatics mediated by a DDQ/TFA oxidation system has been developed for the construction of 9,10-diary-lphenanthrenes (DAPs). The formation of a benzylic carbocation species possessing a quaternary sp3-carbon center on the fluorene moiety by an intermolecular oxidative Friedel-Crafts reaction of two different arenes successfully triggered the subsequent ring expansion to afford DAPs.
- Jin, Tienan,Yang, Lu,Gridnev, Ilya D.,Terada, Masahiro
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supporting information
p. 8920 - 8924
(2020/12/02)
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- Manganese-Catalyzed Synthesis of Quaternary Peroxides: Application in Catalytic Deperoxidation and Rearrangement Reactions
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Highly efficient, selective, and direct C-H peroxidation of 9-substituted fluorenes has been achieved using a Mn-2,2′-bipyridine catalyst via radical-radical cross-coupling. Moreover, this method effectively promotes the vicinal bisperoxidation of sterically hindered various substituted arylidene-9H-fluorene/arylideneindolin-2-one derivatives to afford highly substituted bisperoxides with high selectivity over the oxidative cleavage of Ca C bond that usually forms the ketone of an aldehyde. Furthermore, a new approach for the synthesis of (Z)-6-benzylidene-6H-benzo[c]chromene has been achieved via an acid-catalyzed skeletal rearrangement of these peroxides. For the first time, unlike O-O bond cleavage, reductive C-O bond cleavage in peroxides using the Pd catalyst and H2 is described, which enables the reversible reaction to afford exclusively deperoxidized products. A detailed mechanism for peroxidation, molecular rearrangement, and deperoxidation has been proposed with preliminary experimental evidences.
- Chaudhari, Moreshwar B.,Gnanaprakasam, Boopathy,Shaikh, Moseen A.,Ubale, Akash S.
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p. 10488 - 10503
(2020/09/23)
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- Sequential Cross-Coupling/Annulation of ortho-Vinyl Bromobenzenes with Aromatic Bromides for the Synthesis of Polycyclic Aromatic Compounds
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A sequential cross-coupling/annulation of ortho-vinyl bromobenzenes with aromatic bromides was realized, providing a direct and modular approach to access polycyclic aromatic compounds. A vinyl-coordinated palladacycle was proposed as the key intermediate for this sequential process. Excellent chemoselectivity and regioselectivity were observed in this transformation. The practicability of this method is highlighted by its broad substrate scope, excellent functional group tolerance, and rich transformations associated with the obtained products.
- Wei, Dong,Li, Meng-Yao,Zhu, Bin-Bin,Yang, Xiao-Di,Zhang, Fang,Feng, Chen-Guo,Lin, Guo-Qiang
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supporting information
p. 16543 - 16547
(2019/11/03)
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- Br?nsted acid-catalysed hydroarylation of unactivated alkynes in a fluoroalcohol-hydrocarbon biphasic system: Construction of phenanthrene frameworks
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Transition metal-free hydroarylation of unactivated alkynes was achieved by combining a Br?nsted acid catalyst and a two-phase solvent system consisting of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) and cyclohexane. This protocol is applicable to a wide variety of 2-alkynylbiaryls which leads to the synthesis of substituted phenanthrenes via 6-endo-selective ring closure. The biphasic system achieves highly efficient ring closure by appropriate separation of cationic intermediates from neutral compounds. The vinyl carbocation intermediates are stabilised in the HFIP phase, while the substrates and products are distributed in the cyclohexane phase to suppress intermolecular side reactions.
- Takahashi, Ikko,Fujita, Takeshi,Shoji, Noriaki,Ichikawa, Junji
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supporting information
p. 9267 - 9270
(2019/08/08)
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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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- Base-Promoted Oxidative C(sp3)–S Bond Cross-Coupling of Inactive Fluorenes and Thiols for the Synthesis of 9-Monothiolated Fluorenes
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The highly efficient and selective C(sp3)–S bond cross-coupling method for the synthesis of 9-thiolated fluorenes through a direct thiolation at 9-C(sp3)–H of fluorenes with thiols is described. This reaction occurs at ambient conditions and shows good tolerance of functional groups including arylthiols and alkylthiols. A wide range of products is obtained in moderate to good yields. Besides, the reaction of benzothiophenol and fluorine generates unexpected 9-benzylidene-9H-fluorene by eliminating hydrogen sulfide.
- Liu, Yafeng,Yuan, Xinglong,Su, Kexin,Tian, Yuan,Chen, Baohua
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supporting information
p. 1649 - 1652
(2019/01/30)
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- Synthesis of 1,2-diarylethylenes by Pd-catalyzed one-pot reaction of benzyl halides, tosylhydrazide, and aryl aldehydes
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Background: Substituted olefins are versatile functional groups and intermediates in chemistry, medicine, electronics, and optics and materials science fields because of their unique properties. One important class of substituted olefins 1,2-diarylethylenes have attracted considerable attention due to their presence in both natural products and pharmacologically active substances. Methods: In this paper, we developed a one-pot two-step coupling reaction of aryl aldehydes, tosylhydrazide with benzyl halides by using inexpensive Pd(PPh3)4 as catalyst, leading to a variety of 1,2- diphenylethenes derivatives with moderate to good yields. Results: The desired 1,2-diarylethylenes were obtained in 46-96% yields via Pd(0)-catalyzed one-pot reaction of benzyl halides, tosylhydrazide, and aryl aldehydes. Conclusion: The catalytic system presented here enables the use of easily accessible starting materials and good functional group tolerance.
- Shen, Xu,Liu, Ping,Liu, Yan,Dai, Bin
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p. 709 - 715
(2018/07/14)
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- A Rapid and Highly Efficient Method for the Synthesis of Benzofulvenes via CsOH-Catalyzed Condensation of Indene and Aldehydes
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A fast condensation of indene with a wide range of aldehydes catalyzed by cesium hydroxide monohydrate (CsOH·H2O) for the synthesis of benzofulvenes with good to excellent yields was demonstrated. The condensation can be completed within a few minutes under room temperature and air atmosphere without the use of special ligands or phase-transfer catalysts. In addition, the ratio of indene to aldehydes played an important role in this reaction. The single condensation products 3 can be obtained as main products with a ratio of 1.2:1, whereas the double condensation products 4 can be obtained by changing the ratio to 1:2.2. This protocol provides an efficient, simple and general method for the synthesis of benzofulvenes 3 and double condensation products 4, which are important intermediates in the synthesis of numerous drugs and natural products.
- Yi, Rongnan,Chen, Jinyang,Wang, Xueyan,Liang, Zhiwu,Xu, Xinhua
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supporting information
p. 1347 - 1351
(2018/04/02)
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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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- Aldehyde/ketone-catalyzed highly selective synthesis of 9-monoalkylated fluorenes by dehydrative C-alkylation with primary and secondary alcohols
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By using aldehydes or ketones as the catalyst and screening CsOH out as the more effective base than KOH in many instances, an efficient 9-C-alkylation of fluorenes with alcohols was achieved to provide a green and practical method for general synthesis of the useful 9-monoalkylated fluorenes in high selectivities. This new method tolerates a wide range of substrates including activated and unactivated primary and secondary alcohols, thus solving the issues remaining in the field and largely broadening the diversity of the 9-monoalkylated fluorenes. Consequently, fine-tuning of the alkylated fluorenes was made possible to provide specific fluorene monomers for function-oriented polyfluorenes. Preliminary mechanistic studies revealed that the external carbonyl compounds can be quantitatively regenerated and recovered in the reaction cycle.
- Chen, Jianhui,Li, Yang,Li, Shuangyan,Liu, Jianping,Zheng, Fei,Zhang, Zhengping,Xu, Qing
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supporting information
p. 623 - 628
(2017/08/17)
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- Pd-Catalyzed Autotandem Reactions with N-Tosylhydrazones. Synthesis of Condensed Carbo- and Heterocycles by Formation of a C-C Single Bond and a C-C Double Bond on the Same Carbon Atom
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A new Pd-catalyzed autotandem reaction is introduced that consists of the cross-coupling of a benzyl bromide with a N-tosylhydrazone followed by an intramolecular Heck reaction with an aryl bromide. During the process, a single and a double C-C bond are formed on the same carbon atom. Two different arrangements for the reactive functional groups are possible, rendering great flexibility to the transformation. The same strategy led to 9-methylene-9H-fluorenes, 9-methylene-9H-xanthenes, 9-methylene-9,10-dihydroacridines, and also dihydropyrroloisoquinoline and dihydroindoloisoquinoline derivatives.
- Paraja, Miguel,Valdés, Carlos
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supporting information
p. 2034 - 2037
(2017/04/27)
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- ORGANIC ELECTROLUMINESCENT DEVICE BASED ON NEUTRAL FREE-RADICAL ELECTROLUMINESCENT MATERIAL
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Disclosed is an organic electroluminescent device, wherein the light-emitting layer is composed of a non-doped neutral free-radical electroluminescent material or a neutral free-radical electroluminescent material doped in a matrix material. The luminesce
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- Carboxylic acid-catalyzed highly efficient and selective hydroboration of alkynes with pinacolborane
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We have demonstrated for the first time that carboxylic acids are able to catalyze the direct hydroboration of various terminal and internal alkynes with pinacolborane without using any metal catalysts. This unprecedented catalytic hydroboration exhibits
- Ho, Hon Eong,Asao, Naoki,Yamamoto, Yoshinori,Jin, Tienan
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p. 4670 - 4673
(2015/01/09)
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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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- 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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- Dications of benzylidenefluorene and diphenylmethylidene fluorene: The relationship between magnetic and energetic measures of antiaromaticity
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Oxidation of m- and p-substituted benzylidene fluorenes to antiaromatic dications was attempted by electrochemical and chemical means. Electrochemical oxidation to dications was successful for benzylidene fluorenes with p-methoxy, p-methyl, p-fluoro, and
- Do, Catherine,Hatfield, Julianne,Patel, Shirali,Vasudevan,Tirla, Cornelia,Mills, Nancy S.
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supporting information; experimental part
p. 181 - 187
(2011/03/19)
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- A comparative study in oxidative free radical reactions between 9-benzylidene-9-h fluorene derivatives and β-dicarbony1 compounds in the presence of mn(oac) 3 and can
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The reactions of some 1,3-dicarbonyl compounds with 9-benzylidene-9-H- fluorene derivatives in the presence of manganese(III)acetate and ceric ammonium nitrate (CAN) were searched. 9-benzylidene-9-H-fluorene compounds form mainly [2+3] dipolar cycloadditi
- Demirhan, Hulya,Arslan, Mustafa,Zengin, Mustafa,Kucukislamoglu, Mustafa
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scheme or table
p. 488 - 494
(2012/04/23)
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- Palladium complexes with carbene and phosphine ligands: Synthesis, structural characterization, and direct arylation reactions between aryl halides and alkynes
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The new palladium complexes with NHC and phosphine ligands, cis-PdCl 2(L2)(PPh3) (2), cisPdBr2(L 2)(PPh3) (3), and cis-PdCl2(L 3)(PPh3) (4) were prepared following a general protocol of a one pot reaction between PdCl2(COD), PPh3, and the ligand precursors LH · Y (Y = Cl, Br, BF4) (L2 = l,3-dibenzylimidazolin-2-ylidene; L3 = l,3-dibenzylimidazol-2- ylidene). The cis-PdCl2(L3)(PCy3) complex (5) was prepared by the ligand substitution reaction between 4 and PCy3. The palladium complexes with NHC and pyridine complexes, trans-PdCl 2(L)(py) (6: L = L2; 7: L = L3) were obtained by heating a mixture Of PdCl2(COD) and LH · BF4 in pyridine. A similar reaction condition using CH3CN as solvent with KO'Bu as base afforded cis-PdCl2(L3)2 (8). Complexes 2-8 were successfully characterized by X-ray crystallographic studies, among which, intriguingly, two polymorphs of 8 were obtained. Thermogravimetric analysis showed that the Cis-PdX2(NHC)(PR3) complexes are more thermally stable than the trans-PdCl2(NHC)(py) complexes. Together with the known Cis-PdCl2(L1(PCy3) (1) (L1 = l-benzyl-3-(N-phenylacetamido)imidazol-2-ylidene), they were screened for the direct arylation reaction between aryl halides and alkynes. The result indicate that the carbene/phosphine complexes 1-5 are superior precatalysts than 6-8 with higher activities than the commonly-used system of Pd(OAc)2/2PPh3.
- Chan, Kai-Ting,Tsai, Yi-Hua,Lin, Wu-Shien,Wu, Jia-Rong,Chen, Shih-Jung,Liao, Fu-Xing,Hu, Ching-Han,Lee, Hon Man
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scheme or table
p. 463 - 472
(2010/03/25)
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- Synthesis of fluorenes via the palladium-catalyzed 5-exo-dig annulation of o-alkynylbiaryls
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The direct palladium-catalyzed intramolecular hydro arylation of o-alkynylbiaryls proceeded in a highly stereoselective manner producing fluorenes 2, the products of 5-exo-dig cyclization, in excellent yields. The cascade intermolecular arylation, incorpo
- Chernyak, Natalia,Gevorgyan, Vladimir
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experimental part
p. 1101 - 1114
(2009/12/07)
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- Exclusive 5-exo-dig hydroarylation of o-alkynyl biaryls proceeding via C-H activation pathway
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The first example of the palladium-catalyzed exclusive 5-exo-dig hydroarylation of o-alkynyl biaryls has been demonstrated. In contrast to the reported earlier carbocyclizations proceeding via the Friedel-Crafts mechanism, this hydroarylation efficiently proceeds with electron-neutral and electron-deficient arenes, producing fluorene frameworks with defined stereochemistry of the double bond. On the basis of the high reactivity of electron-deficient arenes toward cyclization, high values of inter- and intramolecular kinetic isotope effects, and the exclusive cis-selectivity of cyclization, a mechanism involving a C-H activation motif has been proposed for this transformation. Copyright
- Chernyak, Natalia,Gevorgyan, Vladimir
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p. 5636 - 5637
(2008/12/22)
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- Iodine induced transformations of alcohols under solvent-free conditions
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Iodine has been shown to be an efficient catalyst for transformations of alcohols under solvent-free conditions. In the presence of 5% of iodine, tertiary alcohols underwent dehydration forming the corresponding alkenes, while in the case of 2-phenylpropane-2-ol cyclodimerisation to 1,1,3-trimethyl-3-phenylindane took place. Secondary and primary benzyl alcohols under the same conditions gave the corresponding ethers.
- Stavber, Gaj,Zupan, Marko,Stavber, Stojan
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p. 8463 - 8466
(2007/10/03)
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- Synthesis of fused polycycles by 1,4-palladium migration chemistry
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Novel palladium migration/arylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement with the idea that these palladium-catalyzed C-H activation reactions parallel electrophilic aromatic substitution.
- Huang, Qinhua,Campo, Marino A.,Yao, Tuanli,Tian, Qingping,Larock, Richard C.
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p. 8251 - 8257
(2007/10/03)
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- Synthesis of 9-alkylidene-9H-fluorenes by a novel palladium-catalyzed rearrangement
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(matrix presented) In the presence of a palladium catalyst and NaOAc, aryl iodides react with 1-aryl-1-alkynes to afford 9-alkylidene-9H-fluorenes in good yields. This process appears to involve (1) oxidative addition of the aryl iodide to Pd(0), (2) alkyne insertion, (3) rearrangement of the resulting vinylic palladium intermediate to an arylpalladium species, and (4) aryl-aryl coupling with simultaneous regeneration of the Pd(0) catalyst.
- Tian, Qingping,Larock, Richard C.
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p. 3329 - 3332
(2007/10/03)
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- Heterocyclic free radicals. Part 1. 4,5-Diazafluorene derivatives of Koelsch's free radical: an EPR and metal-ion complexation study
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Heteroaromatic precursors to nitrogen substituted derivatives of Koelsch's free radicals have been prepared by the condensation of 4,5-diazafluorene with a fluorenylidene or diazafluorenylidene. These compounds appear coloured and can exist in different tautomeric forms. An improved one pot synthesis of 4,5-diazafluorenone has been developed by the oxidative ring contraction of 1,10-phenanthroline with aqueous potassium permanganate. Aza derivatives of Koelsch's free radical are easily generated by oxidation of the appropriate precursors with K3Fe(CN)6. Treatment of 9-[(9H-4,5-diazafluoren-9-ylidene)phenylmethyl]-9H-fluoren-9-yl radical with CuCl2 in EtOH gives a brown precipitate of a 1:1 radical-ligand complex.
- Plater, M. John,Kemp, Steven,Lattmann, Eric
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p. 971 - 980
(2007/10/03)
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- Synthesis of a 9-fluorenone derived β-amino alcohol ligand depicting high catalytic activity and pronounced non-linear stereochemical effects
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The Jacobsen epoxidation of 9-alkylidenefluorenes 4a (ethylidene), 4b (benzylidene) and 4c (1-naphtylmethylene) with standard (R,R)-manganese salen catalyst has been studied. Both conversion and enantioselectivity depend on the steric bulk of the olefin substituent, best results being recorded with 4b (96% yield, 99% ee). The stereochemical course of the epoxidation of 4a is highly dependent on temperature and solvent, the ee of the resulting epoxide (S)-5a varying from 22% (-18°C, CH2Cl2) to 49% (55°C, MTBE). The lithium perchlorate induced ring-opening of 5a with piperidine in MeCN affords a mixture of regioisomeric amino alcohols 3a/2a arising from the amine attack at the more substituted and less substituted carbons, respectively. The 3a/2a ratio can be modulated by the LiClO4 concentration and the reaction temperature, and varies from 44:56 to 91:9. An independent, completely regiocontrolled synthesis of 3a has been developed involving ring-opening by the more substituted carbon of epoxide 5a with diisopropoxytitanium diazide, reduction of azidoalcohol 10a (H2, Pd/C) and cycloalkylation (1,5- dibromopentane, K2CO3) of the amino alcohol 11a. The amino alcohol 3a exhibits a positive nonlinear stereochemical effect in its action as a ligand for the enantioselective addition of Et2Zn to benzaldehyde. The use of regiochemically pure 3a of >99% ee has been studied in the addition of Et2Zn to a representative family of aldehydes [19 examples, 93.6% mean ee]. The use of the directly available 9:1 mixture of 3a and 2a derived from 46-47% ee 5a as a ligand system for the enantioselective addition of Et2Zn to aldehydes [8 examples, 93.1% mean ee] is also reported.
- Reddy, Katamreddy Subba,Sola, Lluis,Moyano, Albert,Pericas, Miquel A.,Riera, Antoni
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p. 165 - 176
(2007/10/03)
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- A critical analysis of the mechanistic basis of enantioselectivity in the bis-cinchona alkaloid catalyzed dihydroxylation of olefms
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This paper presents a critical analysis of two transition state models for the bis-cinchona alkaloid catalyzed enantioselective dihydroxylation of olefms using a broad range of experimental data. In one model (Sharpless) the transition state resembles a m
- Corey,Noe, Mark C.
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p. 11038 - 11053
(2007/10/03)
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- Potassium fluoride supported on alumina induced aldol condensation of fluorene
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In the presence of potassium fluoride supported on alumina as a solid base, fluorene condensated smoothly with aromatic aldehydes in DMF at 150°C to give dibenzofulvenes in fair yield (44-90%).
- Lu, Wen-Xing,Yan, Chao-Guo,Yao, Rong
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p. 3719 - 3723
(2007/10/03)
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- Photochemical Formation and Electrophilic Reactivities of Vinyl Cations. Influence of Substituents, Anionic Leaving Groups, Solvents, and Excitation Wavelength on Photoheterolysis and Photohomolysis of 1-(p-R-Phenyl)-2-(2,2'-biphenyldiyl)vinyl Halides
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Using product analysis and time-resolved laser flash photolysis techniques, the photochemistry at λexc ca. 250 and 310 nm (exc = excitation) of 1-(p-R-phenyl)-2-(2,2'-biphenyldiyl)vinyl halides (R = H, Me, MeO) in methanol and acetonitrile at room temperature was studied.The title compounds undergo photoheterolysis and photohomolysis to give vinyl cations =C+- (carbenium ions) and vinyl radicals =C.-.The cation : radical ratio increases with electron-donating strength of the substituent R, H - - - -, indicating that the cleavage of the C-X bond to yield cation and halide anion proceeds, in the rate-determining step, by heterolysis and not by homolysis followed by electron transfer in the radical pair.The cation : radical ratio is solvent dependent: e.g., for the vinyl bromide with R = MeO and with λexc = 308 nm, in CH2Cl2 as solvent, only radical is observed, in comparison with only cation in the much more polar solvent acetonitrile.In acetonitrile-methanol mixtures, the absolute yields of both cation and radical go through a maximum as the methanol content is increased, however, the catio : radical ratio decreases continuously with increasing .For a particular R, the quantum yield for C-X bond cleavage is higher at ca. 250 than at ca. 310 nm.Also, the cation : radical ratio is wavelength-dependent: at λexc ca. 310 nm there is relatively more heterolysis than at λexc ca. 250 nm.Rate constants for reaction of the cations with nucleophiles were determined in acetonitrile.Those for reaction of the cation with R = MeO (lifetime in acetonitrile 7 μs) with anionic nucleophiles such as the halides are at the diffusion limit in this solvent, ca. 2 * 1010 M-1 s-1, whereas those for reaction with water, alcohols, and cyclic ethers are of the order 105-106 M-1 s-1.The less stabilized cation (R = Me) reacts with alcohols faster by the factor ca. 100, and it decays in acetonitrile ca. 100 times more rapidly.Also, 1-(p-R-phenyl)-2-dimehtylvinyl bromides (R = H, Me, MeO) were photolyzed in acetonitrile.In the case of R = MeO, the cation p-CH3O-C6H4-C+=CMe2 was seen (lifetime 770 ns), and its reactivity with alcohols (k values of 106-107 M-1 s-1) and halides (k values of 1010 M-1 s-1) was determined.The vinyl radicals =C.- react with O2 to yield vinylperoxyl radicals =C-O2. which have absorption maxima at ca. 390 nm.
- Verbeek, Jan-Maarten,Stapper, Marion,Krijnen, Erik S.,Loon, Jan-Dirk van,Lodder, Gerrit,Steenken, Steen
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p. 9526 - 9536
(2007/10/02)
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- Facile synthesis of 1,2-diaryl- and triarylethenes with supported fluoride bases
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Differently substituted arenecarbaldehydes, mainly benzaldehydes, can be very efficiently condensed with a wide variety of methylbenzenes having an electron-withdrawing group in the para-position, as well as with fluorenes, xanthene, cyclopentadienes and indenes by using a standardized KF- or CsF-Al2O3 base system in dimethylformamide.
- Hellwinkel,Goke,Karle
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p. 973 - 978
(2007/10/02)
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- Characterization of the Excited-State Reactivity of a Persistent Aryl-Substituted Allyl Free Radical
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A family of stable aryl-substituted allyl radicals 1 (9H-fluoren-9-yl-9--9-ylidenephenylmethyls) has been characterized by electronic absorption spectroscopy, semiempirical (AM1) molecular orbital calculations, and cyclic voltammetry.Photolysis of 1a in aerated solvents that are poorer hydrogen atom sources than toluene resulted in oxygenation (ΦOX ca. 5 * 10-4) and cleavage products.A thermally reversible photocyclization mechanism is proposed to explain the oxygenation of 1a in inert solvents.Enhanced excited-state reactivity toward hydrogen and halogen atom donors was observed during the steady-state photolysis of 1a.Electron transfer from naphthalene to an excited state of 1a produces an extremely short lived (30 ps) 1a anion/naphthalene radical cation geminate pair.
- Breslin, David T.,Fox, Marye Anne
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p. 13341 - 13347
(2007/10/02)
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- Le (chlorodiisopropyl)silyl fluorenyllithium: un equivalent synthetique du diisopropyl(fluorenylidene)silene
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The metalation of chlorodiisopropylfluorenylsilane 1 with n-butyllithium leads to the α-silylthio compound 3.Compound 3 has a surprising stability and does not afford the diisopropyl(fluorenylidene)silene but behaves as its synthetic equivalent; i.e. it is a useful reagent for "Wittig-Peterson" reactions with various carbonyl compounds leading readily to diisopropylsilanone and fluorenylidene derivatives.
- Couret, C.,Escudie, J.,Delpon-Lacaze, G.,Satge, J.
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p. 233 - 242
(2007/10/02)
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- PHOSPHORORGANISCHE VERBINDUNGEN 120. VERSUCHE ZUM NACHWEIS VON "PHOSPHENEN" AUS GEEIGNETEN PHOSPHINSAEUREDERIVATEN DURCH ELIMINIERUNG
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Phosphinicacidhalogenides with the structure C are reacted with strong bases in the presence of carbonylcompounds.The eventually as intermediates formed "phosphenes" lead with carbonyl compounds to olefines following the course of the "PO-activated olefination".The intermediates don't react with olefines (stilbene or cyclopentadiene) to an isolable adduct.Key words: Phosphinicacidhalides; phosphenes as intermediates; PO-activated olefination; synthesis of olefines.
- Weidert, Peter J.,Geyer, Ekkehard,Horner, Leopold
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- METHYLENE-CARBONYL CONDENSATIONS OF SOME CH ACIDS WITH ALDEHYDES UNDER THE CONDITIONS OF PHASE-TRANSFER CATALYSIS OR CATALYSIS BY THE FLUORIDE ION
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The condensation of a series of CH acids (fluorene, phenylacetonitrile, ethene) with aromatic aldehydes was realized in the aqueous sodium hydroxide-organic solvent-phase-transfer catayst system. 9-Substituted fluorenes do not enter into condensation under the indicated conditions.The condensation of fluorene, PhCH2CN, CH2(CN)2, and CH2(CN)COOEt with benzaldehyde and also of CH2(CN)COOEt with cyclohexanone was realized in the presence of tetrabutylammonium fluoride , deposited on silika gel.It was shown that the yield of the produt from crotonic condensation in the reaction of CH2(COOEt)2 with benzaldehyde is small, and this is due to the instability of PhCH=C(COOEt)2 under the reaction conditions.Sodiomalonic ester was condensed with benzaldehyde in the presence of titanium tetrachloride or aluminum chloride.
- Beletskaya, I.P.,Gulyukina, N.S.,Ali Ali, Muhamed,Solov'yanov, A.A.,Reutov, O.A.
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p. 657 - 661
(2007/10/02)
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- PHOTOLYSIS OF THE VINYL BROMIDE 9-(α-BROMOBENZYLIDENE)FLUORENE IN METHANOL. EFFECT OF WAVELENGTH OF IRRADIATION, SODIUM METHOXIDE AND OXYGEN.
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A quantitative study of the photosolvolysis of 9-(α-bromobenzylidene)fluorene (1) in methanol reveals that the wavelength of irradiation, the presence of sodium methoxide and the presence of oxygen strongly influence the product distribution and the quantum yields of the reaction.
- Verbeek, J. M.,Cornelisse, J.,Lodder, G.
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p. 5679 - 5684
(2007/10/02)
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- ACTIVATION DE LA LIAISON C-H FAIBLEMENT ACIDE PAR ADSORPTION SUR KF-Al2O3
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Condesation of poorly acidic carbon compounds (pka 18-30) with benzaldehyde was achieved by adsorption without solvent on KF-Al2O3.KF-Al2O3 appears as a stronger base than KF.
- Villemin, Didier,Ricard, Michele
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p. 1059 - 1060
(2007/10/02)
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- Studies of the Borderline between Concerted and Stepwise Mechanisms of Elimination : E1cB Elimination of Fluoren-9-ylmethyl Carboxylate Esters
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Rates of β-elimination of carboxylate leaving groups from fluoren-9-ylmethyl carboxylate esters in methanolic sodium methoxide at 25 deg C are reported.An E1cB mechanism with rate-determining formation of a carbanion intermediate is assigned on the basis of near identity of measured elimination rates and rates of carbanion formation predicted from a Taft correlation, and the similarity with elimination of 1-(1-acetoxy-1-methylethyl)indene for which the mechanism has been established by Ahlberg and Thibblin.Values of ρ=0.42 and βlg=0.27 measured for substituted benzoate leaving groups are a little larger than expected (ca. 0.24 and 0.18, respectively) and the discrepancy is tentatively ascribed to conformational enhancement of remote substituent effects, rather than to a contribution of E2 elimination.The effects of alkyl and aryl substitution α to the leaving group are discussed, especially in relation to the borderline between concerted and stepwise mechanisms.The measurements fail to confirm an earlier inference that the borderline shows a discontinuity in transition-state structure at the point of mechanistic change.
- O'Ferrall, Rory A. More,Larkin, Finbar,Walsh, Peter
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p. 1573 - 1580
(2007/10/02)
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- REACTIVITY OF CARBANIONS. X. EFFECT OF THE COUNTERION AND SOLVENT IN THE REACTION OF ALKALINE SALTS OF FLUORENE AND 9-PHENYLFLUORENE WITH BENZALDEHYDE
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Alkaline (Li, Na, K, Cs) and tetrabutylammonium salts of fluorene reversibly add to benzaldehyde in dimethoxyethane, ether, benzene, and hexamethylphosphorotriamide (HMPTA) to form phenyl(9-fluorenyl)carbinolate.A subsequent irreversible elimination of the base molecule leads to benzylidenefluorene.The equilibrioum between the starting reagents and the addition products in the reaction of alkaline derivatives of 9-phenylfluorene with benzaldehyde may be shifted in any direction by varying the cation size or the nature of the solvent.A general feature is a decrease in reaction rate with increasing radius of the alkali cation and the solvating capacity of the solvent.
- Beletskaya, I. P.,Solov'yanov, A. A.,Karpyuk, A. D.,Kucheryavenko, O. P.,Reutov, O. A.
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p. 1179 - 1183
(2007/10/02)
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- Effect of Bulky Size of Carbonyl Systems on Betaine Decomposition of Semi-stablized Arsonium Ylids
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Reactions of substituted benzylidentriphenylarsenanes (2a-i) with 9-anthraldehyde and 9-fluorenone have been studied using benzene-sodamide, chloroform-sodium hydride and methanol-sodium ethoxide as solvent-base pairs.In all the cases olefins (5a-i and 6a-i) are formed exclusively.Variation of solvents and bases has no effect on the course of betaine decomposition formed by the nucleophilic attack of ylids on carbonyl systems.
- Gupta, K. C.,Srivastava, N.,Nigam, R. K.
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p. 802 - 803
(2007/10/02)
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- Studies on Betaine Decomposition of Arsonium Ylides
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A systematic study on the nature of decomposition of betaine formed by nucleophilic attack of semistabilized arsonium ylides on thiocarbonyl substrates has been carried out.A series of substituted benzylidenetriphenylarsenanes have been generated from their corresponding salts and condensed with few cyclic thioketones to yield exocyclic olefins as exclusive products.The non-availability of thioepoxides indicates that the mode of decomposition of such type of betaines is quite analogous to the betaine formed by phosphonium ylides.The structure of the products have been assigned by IR and NMR spectral studies. - Keywords: Betaine, Arsonium Ylides
- Tewari, R. S.,Suri, S. K.,Gupta, K. C.
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