- 1,n-Radical Ions. The Electrochemical Oxidation of 1,1,2,2-Tetraphenylcyclopropane
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The anodic oxidation of 1,1,2,2-tetraphenylcyclopropane leads to 1,1,3-triphenylindene or tetraphenylallene depending on the basicity of the medium.
- Wayner, Danial D. M.,Arnold, Donald R.
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- Rhodium(I)-Catalyzed Arylation/Dehydroxylation of tert-Propargylic Alcohols Leading to Tetrasubstituted Allenes
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Diverse tetrasubstituted allenes are obtained selectively by the reaction of tert-propargylic alcohols and arylboroxines under rhodium catalysis. The reaction is assumed to proceed through an arylation/dehydroxylation process, which involves β-hydroxide elimination of a β-hydroxy alkenyl-rhodium intermediate that is generated by regioselective arylrhodation of the tert-propargylic alcohol. In addition, when enantioenriched propargylic alcohol was used to prepare optically active allene, high efficiency of central-to-axial chirality transfer was observed. The application of current method to structural modification of pharmaceutical drugs was also showcased by a highly diastereoselective transformation of mifepristone. (Figure presented.).
- Liu, Na,Zhi, Yanle,Yao, Jian,Xing, Junhao,Lu, Tao,Dou, Xiaowei
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- Metal-free hydrogenation of electron-poor allenes and alkenes
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The poorer, the better: A metal-free catalytic procedure for the reduction of electron-poor allenes and alkenes has been developed. The method employs a frustrated Lewis pair based catalyst. 1,4-Diazabicyclo[2.2.2]octane (DABCO)/B(C6F5)3 was shown to be the best combination in optimization studies. Copyright
- Ines, Blanca,Palomas, David,Holle, Sigrid,Steinberg, Sebastian,Nicasio, Juan A.,Alcarazo, Manuel
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supporting information
p. 12367 - 12369
(2013/02/22)
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- Synthesis of tetraarylallenes via palladium-catalyzed addition-elimination reactions of 1,1,3-triaryl-2-propyn-1-ols with aryl iodides
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The palladium-catalyzed reactions of tert-propargylic alcohols with aryl iodides afforded tetraarylallenes in good yields. This reaction involves: (1) oxidative addition of the aryl iodide to Pd(O); (2) arylpalladium intermediate coordination to the carbon-carbon triple bond of the 1,1,3-triaryl-2-propyn-1-ol and subsequent regioselective insertion of the alkynol to form β-hydroxyvinylpalladium species; and (3) β-elimination to produce the tetraarylallenes. Generally, the best results are obtained by employing 5 mol% of Pd(TFA)2, 10 mol% of PPh3, two equivalents of aryl iodide and five equivalents of Et3N in MeCN. Georg Thieme Verlag Stuttgart.
- Wei, Li-Mei,Wei, Li-Lan,Pan, Wen-Bin,Wu, Ming-Jung
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p. 2219 - 2223
(2007/10/03)
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- Reactions of the Lithium Salts of the Tribenzylidenemethane Dianion, Diphenylacetone Dianion, and Related Compounds
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Potentially synthetically useful reactions of the dilithium salts of the title dianions have been investigated. Electrophilic quenching with a variety of reagents usually leads to the expected products in good yield. Quenching the diphenylacetone dianion with 1 equiv of trimethylchlorosilane, however, gives a good yield of 1,3-diphenylallene obtained by formal elimination of a trimethylsiloxy anion from an intermediate monoquenched monoanion salt. NMR studies, however, do not reveal the intermediacy of the 1,3-diphenyl-2-(trimethylsiloxy)allyl anion but rather suggest that the initial reaction site is at carbon, rather than oxygen. Oxidation of the dianions leads either to ring closure or dimerization for the tribenzylidenemethane dianion and to dimerization for the diphenylacetone dianion. The dimerization reactions are stereospecific, both with respect to the two new stereocenters produced and for the double bonds of the bis-silyl enol ether products if the dimeric bis-enolate dianion products are quenched with trimethylchlorosilane.
- Witt, Ortrun,Mauser, Harald,Friedl, Thomas,Wilhelm, Dieter,Clark, Timothy
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p. 959 - 967
(2007/10/03)
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- Clathrate Formers with Allene Structure - Host Compounds, Crystal Inclusion and Structure of a Dioxane Clathrate
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The tetraaryl-substituted allenes 1-8 are synthesized, and their properties in crystal inclusion are determined.Dependent on the type and number of the substituents, host compounds result, which have different inclusion properties and clathrate selectivities.Host 1h forms inclusion compounds with a wide range of apolar and relatively polar cyclic guest solvents (26 inclusions altogether), while 2, 4, 5, and 7b form only one or two inclusions.In two-component solvent systems, high inclusion selectivities are found for the host compounds.The crystal structure of the4*dioxane (1:1) clathrate is reported.Relations between structure and inclusion selectivity are discussed.
- Weber, Edwin,Seichter, Wilhelm,Goldberg, Israel
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p. 811 - 820
(2007/10/02)
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- 1,n-Radical ions. Photosensitized (electron transfer) and electrochemical oxidation of 1,1,2,2-tetraphenylcyclopropane
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The photosensitized (electron transfer) and electrochemical oxidation of 1,1,2,2-tetraphenylcyclopropane (1) have been studied.The products obtained from the photosensitized (electron transfer) study are 1,1,3,3-tetraphenylpropene (2), 1,3,3-triphenylindene (3), tetraphenylallene (4), and 3-methoxy-1,1,3,3-tetraphenylpropene (8).The product ratios are dramatically dependent upon the reaction conditions, particularly sensitizer (aromatic nitriles, tetracyanoethylene, chloranil, and 2,3-dichloro-5,6-dicyanobenzoquinone were used), and solvent.The variation in product ratios are attributed to variations in the redox behaviour of the sensitizer radical anion and upon the basicity and nucleophilicity of the medium.The products in the electrochemical study are 3,4, and 8.Common intermediates have been identified and a mechanism for the formation of product is proposed.
- Wayner, Danial D. M.,Arnold, Donald R.
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p. 871 - 881
(2007/10/02)
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- Lithium 2-Lithio-1,1,3,3-tetraphenylpropenide
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The novel lithium 2-lithio-1,1,3,3-tetraphenylpropenide (2) is shown via (1)H, (13)C, and (7)Li n.m.r. spectroscopy and by chemical means to adopt an ionic allyl-lithium structure with C2v symmetry; the second lithium is covalently bonded to the central (C-2) carbon.
- Bernard, Josef,Schnieders, Christoph,Muellen, Klaus
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- Electrochemical Reduction and Oxidation of Allenes
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The allenes 1 - 3 are reduced on mercury at -2.17 V (sce) (1), -3.12 V (2), and below -3.30 V (3); they are oxidized on glassy carbon at 1.25, 1.65 V (1), 1.75 V (2), and above 2.25 V (3).In the preparative reduction 1 forms, depending on the workup, 86percent of 1,1,3,3-tetraphenyl-1-propene (6a) or up to 50percent of aldehyde 9, a formylation product of the rearranged radical anion intermediate; on carboxylation of the electrolyte 54percent of carboxylic acid 8 are formed.The allene 2 is hydrogenenated to give 30 percent of (E)-1-phenyl-1-propene (10) and hydrodimerized to form 30percent of yield s in methylene dichloride/methanol 61 - 73percent of 2-chloro-1,1,3-triphenylidene (13), which is probably formed by chlorine, that is electrochemically generated from methylene chloride.In methanol/dioxane 13 is not obtained but 71percent of indanone 16 are produced.The oxidation of 2 and 3 is unselective; due to follow-up oxidations many products are formed in low yield.
- Schlegel, Guenter,Schaefer, Hans J.
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p. 960 - 969
(2007/10/02)
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- A NEW METHOD FOR THE PREPARATION OF (2,2-DIPHENYLVINYLIDENE)-TRIPHENYLPHOSPHORANE AND ITS REACTION WITH CARBONYL COMPOUNDS
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Hexaphenylcarbodiphosphorane (I), prepared from triphenylphosphine and carbon tetrahalide, when treated with benzophenone in equimolar ratio, gave the ylide (2,2-diphenylvinylidene)triphenylphosphorane (II) which, upon further treatment with benzophenone, gave 1,3-tetraphenylallene (III) via Witting reaction.
- Verma, S.,Bokadia, M. M.
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