- Strategic Application and Transformation of ortho-Disubstituted Phenyl and Cyclopropyl Ketones to Expand the Scope of Hydrogen Borrowing Catalysis
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The application of an iridium-catalyzed hydrogen borrowing process to enable the formation of α-branched ketones with higher alcohols is described. In order to facilitate this reaction, ortho-disubstituted phenyl and cyclopropyl ketones were recognized as crucial structural motifs for C-C bond formation. Having optimized the key catalysis step, the ortho-disubstituted phenyl products could be further manipulated by a retro-Friedel-Crafts acylation reaction to produce synthetically useful carboxylic acid derivatives. In contrast, the cyclopropyl ketones underwent homoconjugate addition with several nucleophiles to provide further functionalized branched ketone products.
- Frost, James R.,Cheong, Choon Boon,Akhtar, Wasim M.,Caputo, Dimitri F. J.,Stevenson, Neil G.,Donohoe, Timothy J.
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supporting information
p. 15664 - 15667
(2016/01/09)
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- Influence of (2,3,4,5,6-pentamethyl/phenyl)phenyl scaffold: Stereoelectronic control of the persistence of o-quinonoid reactive intermediates of photochromic chromenes
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Regioisomeric photochromic chromenes 1Ch-6Ch substituted with the (2,3,4,5,6-pentamethyl/phenyl)phenyl scaffold were designed to delve into stereoelectronic effects on the spectrokinetic properties of photogenerated o-quinonoid reactive intermediates. While the latter derived from 1Ch, 2Ch, 4Ch, and 5Ch were found to exhibit notable persistence, those from 3Ch and 6Ch were found to revert rapidly at room temperature to preclude visible coloration. The intermediates of 1Ch and 2Ch were found to be marginally more stable than those of 4Ch and 5Ch, respectively, attesting to the possibility of toroidal conjugation via Cipso-π orbitals in the former. The rapid reversion of the intermediates of 3Ch and 6Ch is attributed to unfavorable electronic repulsion between the phenyl ring of the (pentamethyl/phenyl)phenyl scaffold and one of the lone-pairs of the o-quinonoid oxygen. Thus, the regioisomerically substituted photochromic chromenes are shown to permit control of the reversion, very rapidly as well as slowly, of the colored o-quinonoid intermediates through operation of stereoelectronic effects differently.
- Mandal, Susovan,Parida, Keshaba Nanda,Samanta, Subhas,Moorthy, Jarugu Narasimha
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scheme or table
p. 7406 - 7414
(2011/11/06)
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- Role of substitution on the photophysical properties of 5,5′-diaryl-2,2′-bipyridine (bpy*) in [Ir(ppy) 2(bpy*)]PF6 complexes: A combined experimental and theoretical study
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The synthesis of a family of 4′-functionalized 5,5′-diaryl-2, 2′-bipyridines (bpy*; 6a-6g) is reported. These ligands were reacted with the dimer [(ppy)2IrCl]2 (ppyH = 2-phenylpyridine) and afforded, after subsequent counterion exchange, a new series of luminescent cationic heteroleptic iridium(III) complexes, [(ppy)2Ir(bpy*)] PF6 (8a-8g). These complexes were characterized by electrochemical and spectroscopic methods. The crystal structures of two of these complexes (8a and 8g) are reported. All of the complexes except for 8c and 8f exhibit intense and long-lived emission in both 2-MeTHF and ACN at 77 K and room temperature. The origin of this emission has been assigned by computational modeling to be an admixture of ligand-to-ligand charge-transfer [3LLCT; π(ppy) → π*(bpy*)] and metal-to-ligand charge-transfer [ 3MLCT; dπ(Ir) → π*(bpy*)] excited states that are primarily composed of the former. The luminescent properties for 8a-8c are dependent upon the functionalization at the 4′ position of the aryl substituents affixed to the diimine ligand, while those for 8d-8g are essentially independent because of an electronic decoupling of the aryls and bpy due to the substitution of o,o-dimethyl groups on the aryls, causing a near 90° angle between the aryl and bipyridyl moieties. A combined density functional theory (DFT)/time-dependent DFT study was conducted in order to understand the origin of the transitions in the absorption and emission spectra and to predict accurately emission energies for these complexes.
- Ladouceur, Sebastien,Fortin, Daniel,Zysman-Colman, Eli
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scheme or table
p. 5625 - 5641
(2010/08/04)
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- Synthesis of arylbromides from arenes and Nbromosuccinimide bromosuccinimide (NBS) in acetonitrile - A convenient method for aromatic bromination
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Regioselective and chemoselective electrophilic bromination of a wide series of activated arenes using N-bromosuccinimide (NBS) in acetonitrile occurs readily. Environmentally friendly conditions, large substrate scope, and ease of synthesis enhance the utility of this method over other electrophilic bromination conditions.
- Zysman-Colman, Eli,Arias, Karla,Siegel, Jay S.
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experimental part
p. 440 - 447
(2009/12/01)
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- Positional Reactivity of Acylpolymethylbenzenes in Electrophilic Substitution
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Friedel-Crafts acylation, bromination, deuteration, and nitration of acetylpentamethylbenzene (APMB), 1-acetyl-2,3,4,6-tetramethylbenzene (ATMB), and 1-benzoyl-2,3,4,6-tetramethylbenzene (BTMB) and the resulting product distribution were investigated.Friedel-Crafts acylation, bromination, and deuteration of APMB and Friedel-Crafts acylation of ATMB gave deacetylation-substitution products.On the other hand, bromination and deuteration of ATMB (or BTMB) and Friedel-Crafts acylation of BTMB gave 5-substituted products.In both cases, the positional reactivities were in accordance with the relative ?-complex stability.Conversely, except for Friedel-Crafts-type nitration, the positional reactivities in the nitration of these substrates were strikingly different from those of the above three reactions.Thus, side-chain functionalization at the 6-methyl group occurred in nitration with fuming nitric acid, depending on the solvents in use.The NMDO calculations and the reaction of APMB with single-electron transfer reagents such as tetranitromethane-hν or cerium(IV) ammonium nitrate suggest that the product distribution in nitration can be explained in terms of a single-electron transfer mechanism.
- Matsuura, Kazunori,Kimura, Yasuo,Takahashi, Hisakazu,Morita, Toshio,Takahashi, Ichiro,et al.
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p. 757 - 765
(2007/10/02)
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- Halogenation Using Quaternary Ammonium Polyhalides. XIV. Aromatic Bromination and Iodination of Arenes by Use of Benzyltrimethylammonium Polyhalides-Zinc Chloride System
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The reaction of arenes with benzyltrimethylammonium tribromide or benzyltrimethylammonium dichloroiodate in acetic acid in the presence of ZnCl2 at room temperature or at 70 deg C gave brome- or iodo-substituted arenes in good yield, respectively.
- Kajigaeshi, Shoji,Kakinami, Takaaki,Moriwaki, Masayuki,Tanaka, Toshio,Fujisaki, Shizuo,Okamoto, Tsuyoshi
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p. 439 - 443
(2007/10/02)
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- Selective Nuclear Halogenation of Polymethylbenzenes with Alumina-Supported Copper(II) Halides
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The halogenation of polymethylbenzenes with alumina-supported copper(II) halides under heterogeneous conditions in nonpolar solvents gave nuclear-halogenated compounds selectively in high yields; no side-chain-halogenated compounds were formed.
- Kodomari, Mitsuo,Satoh, Hiroaki,Yoshitomi, Suehiko
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p. 4149 - 4150
(2015/06/25)
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- On the Reaction of (Pentamethylcyclopentadienyl)lithium with Halomethanes and Formyl Compounds
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In view to the synthesis of pentamethylcyclopentadienyl-substituted methane derivatives ("pentamethylcyclopentadienyl-carbon compounds") reactions of (pentamethylcyclopentadienyl)lithium with halomethans, formates, and corbon dioxide were investigated.While treatment with tri- and tetrahalomethanes leads to benzene derivatives via molecular rearrangement, reactions with formates and carbon dioxide yield pentamethylcyclopentadienyl-substituted methane derivatives.Attempts to prepare disubstituted species show the formation of by-products only.
- Kohl, Franz X.,Jutzi, Peter
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p. 1539 - 1544
(2007/10/02)
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- ETUDE CINETIQUE DE LA REACTION DE BROMINATION DANS LE SO2 LIQUIDE. REACTIVITES DU BENZENE, DES POLYMETHYLBENZENES ET D'ANISOLES SUBSTITUES. DETERMINATION DES REACTIVITES RELATIVES ET CALCUL DES FACTEURS DE VITESSE PARTIELLE
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Absolute rate constants for the bromination of a series of anisoles and polymethylbenzenes, have been measured in liquid sulfur dioxide at -23 +/- 2 deg C.Rate constants for benzene and toluene were determined by extrapolation as: 9.6E-7 and 4.2E-4 l mol-1 mn-1 respectively.Under these conditions, the bromination of anisole provides 0.56percent ortho- and 98.99percent para-bromoanisole, and the rate relative to benzene is 6.98E8/1.00.These date lead to the partial rate factors for the methoxy group: οOMef = 1.1E7 and pOMef = 4.12E9.The value mOMef = 1.4 is calculated from the rate constant for p-dimethoxy benzene, 10 l mol-1 mn-1.Similarly, in the case of bromination of toluene, a relative rate of 443/1.00, and an isomer distribution of 16percent ortho- and 84percent para, permit the calculation of partial rate for the methyl group:οMef = 212 mMef = 6.4 pMef = 2232 > correlations log k = f(Σ?+), established for the bromination of anisoles and polymethylbenzenes, exhibit large values for their slopes (ρAnisoles+ = -10.51; ρ+polymethylbenzenes = -9.5), and indicate satisfactory additivity of substituent effects.It appears that the + M effect of the methoxy group is less strong in this solvent than it is in water or acetic acid.Despite its low dielectric constant, (D = 17.5 at -20 deg C), liquid sulfur dioxide appearars to be quite a favourable medium for electrophilic aromatic substitution.Thus, for identical experimental conditions, the rate constants for bromination are 1E2 to 1E4 lower than those observed in water, but 1E3 to 1E5 larger than those in acetic acid.
- Castellonese, Paul,Villa, Pierre
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