- PQXdpap: Helical Poly(quinoxaline-2,3-diyl)s Bearing 4-(Dipropylamino)pyridin-3-yl Pendants as Chirality-Switchable Nucleophilic Catalysts for the Kinetic Resolution of Secondary Alcohols
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Helically chiral poly(quinoxaline-2,3-diyl)s bearing 4-(dipropylamino)pyridin-3-yl pendants at the 5-position of the quinoxaline ring (PQXdpap) exhibited high catalytic activities and moderate to high selectivities (up to s = 87) in the acylative kinetic resolution of secondary alcohols. The solvent-dependent helical chirality switching of PQXdpap between pure toluene and a 1:1 mixture of toluene and 1,1,2-trichloroethane enabled the preparation of either compound of a pair of enantiomerically pure alcohols (>99% ee) from a single catalyst.
- Murakami, Ryo,Suginome, Michinori,Yamamoto, Takeshi
-
supporting information
p. 8711 - 8716
(2021/11/24)
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- P-chirogenic Trost ligands mediated asymmetric hydrogenation of simple ketones
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Herein, we report a highly active catalyst system consisting of (Rc,Rc,Rp,Rp)-P-chirogenic Trost ligand and [Ru(C6H6)Cl2]2 for asymmetric hydrogenation of simple ketones, affording the corresponding optically active alcohols in moderate enantioselectivity. A synergetic effect between P- and C-chirogenic centers of the P-chirogenic Trost ligands was observed in this asymmetric hydrogenation process.
- Du, Peng,Liu, Yan-Lan,Lu, Xiao-Bing
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supporting information
(2020/09/22)
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- Enantiopure Methyl- A nd Phenyllithium: Mixed (Carb-)Anionic Anisyl Fencholate-Aggregates
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Methyl- A nd phenyllithium aggregates with enantiopure anisyl fencholate units form after reaction of organolithium reagent with (+)-anisyl fenchol in hydrocarbon and some ethereal solvents. These carbanionic aggregates are characterized by X-ray crystal analyses and exhibit both 3:1 stoichiometry and distorted cubic Li4O3C1 cores, in which three lithium ions coordinate the carbanion (i.e., methylide or phenylide). These three lithium ions define a Lewis acidic surface (Li3), binding the carbanion and expanding with the steric demand of the carbanion (i.e., from Me: 2.62 ?2, over n-Bu: 2.65 ?2 (previous work) to Ph: 2.79 ?2). Methylation and phenylation reactions of various prochiral aldehydes employing these methyllithium and phenyllithium aggregates yield alcohols with up to 44% ee. To rationalize the formation of the mixed (carb-)anionic aggregates, aggregate formation energies, describing co-condensations of RLi (R = Me, Ph, n-Bu) and lithium fencholates, are computed for the 3:1 and 2:2 stoichiometries. These computed aggregate formation energies point to preferences for 3:1 over 2:2 aggregates, as it is also apparent from experimental aggregate formations, confirmed by X-ray crystal analyses. In close analogy to the X-ray crystal structures, the computed Li3 surfaces increase with increasing steric demand of the carbanions. The chiral, mixed (carb-)anionic RLi-fencholate aggregates hence adapt to different carbanion sized and arise not only with small (Me) or primary carbanions (n-Bu) but even with the larger secondary phenyl anion.
- Grote, Vanessa,Neud?rfl, J?rg-Martin,Goldfuss, Bernd
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supporting information
p. 771 - 779
(2019/02/19)
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- Acylative Kinetic Resolution of Alcohols Using a Recyclable Polymer-Supported Isothiourea Catalyst in Batch and Flow
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A polystyrene-supported isothiourea catalyst, based on the homogeneous catalyst HyperBTM, has been prepared and used for the acylative kinetic resolution of secondary alcohols. A wide range of alcohols, including benzylic, allylic, and propargylic alcohols, cycloalkanol derivatives, and a 1,2-diol, has been resolved using either propionic or isobutyric anhydride with good to excellent selectivity factors obtained (28 examples, s values up to 600). The catalyst can be recovered and reused by a simple filtration and washing sequence, with no special precautions needed. The recyclability of the catalyst was demonstrated (15 cycles) with no significant loss in either activity or selectivity. The recyclable catalyst was also used for the sequential resolution of 10 different alcohols using different anhydrides with no cross-contamination between cycles. Finally, successful application in a continuous flow process demonstrated the first example of an immobilized Lewis base catalyst used for the kinetic resolution of alcohols in flow.
- Neyyappadath, Rifahath Mon,Chisholm, Ross,Greenhalgh, Mark D.,Rodríguez-Escrich, Carles,Pericàs, Miquel A.,H?hner, Georg,Smith, Andrew D.
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p. 1067 - 1075
(2018/02/14)
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- Kinetic resolution of secondary carbinols by a chiral N,N-4-dimethylaminopyridine derivative containing a 1,1′-binaphthyl unit: Hydrogen bonding affects catalytic activity and enantioselectivity
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We developed an acylative kinetic resolution of secondary carbinols using a binaphthyl-based N,N-4-dimethylaminopyridine (DMAP) derivative 1d with tert-Alcohol substituents. The reaction proceeded with a wide range of carbinols with moderate to high selectivity (s) (up to s = 79.5). Kinetic studies revealed that catalyst 1d was more catalytically active than the corresponding bis-methyl ether 1d′ or DMAP. Hydrogen bonding between tert-Alcohols of the catalyst and secondary carbinols was responsible for the enhanced reaction rate and high enantioselectivity.
- Fujii, Kazuki,Mitsudo, Koichi,Mandai, Hiroki,Suga, Seiji
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p. 1081 - 1092
(2016/10/11)
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- Synthesis of NHC-Oxazoline Pincer Complexes of Rh and Ru and Their Catalytic Activity for Hydrogenation and Conjugate Reduction
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We describe the preparation and catalytic reactions of new CCN pincer Rh and Ru complexes containing NCH-oxazoline hybrid ligands. Oxazolinyl-phenyl-imidazolium derivatives (3) were suitable ligand precursors for the CCN pincer scaffold. C-H bond activation of 3 with RhCl3·3H2O in the presence of NEt3 yielded the desired CCN pincer Rh complexes 5 in 13-27% yields. The related CCN pincer Ru complexes 8-10 were synthesized in good yields by C-H bond activation of p-cymene Ru complexes 7 in the presence of NaOAc in DMF. The chiral complexes 8 and 9 had two diastereomers according to the coordination of CO and OAc ligands. The CCN Rh complexes showed catalytic activity for conjugate reduction of ethyl β-methylcinnamate with hydrosilane, with moderate enantioselectivity. The CCN Ru complexes were found to be active in the hydrogenation of aromatic ketones. In particular, hydrogenation of 9-acetylanthracene took place at not only the C=O bond but also the anthracene ring. The Ru complexes were also used as catalysts in the transfer hydrogenation of 9-acetylanthracene with 2-propanol; again, both the C=O bond and the anthracene ring were hydrogenated.
- Ito, Jun-Ichi,Sugino, Kanae,Matsushima, Satoru,Sakaguchi, Hiroki,Iwata, Hiroshi,Ishihara, Takahiro,Nishiyama, Hisao
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p. 1885 - 1894
(2016/07/06)
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- Asymmetric transfer hydrogenation of 1-naphthyl ketones by an ansa-Ru(II) complex of a DPEN-SO2N(Me)-(CH2)2(η 6-p-tol) combined ligand
-
The first second-generation designer Ru(II) catalyst 1b featuring an enantiopure N,C-(N-ethylene-N-methyl-sulfamoyl)-tethered (DPEN- κ2N,N′)/η6-toluene hybrid ligand is introduced. Using an S/C = 1000 in HCO2H-Et3N 5:2 transfer hydrogenation medium, secondary 1-naphthyl alcohols are obtained in up to >99.9% ee under mild conditions. Mechanistic factors are discussed.
- Kisic, Andrea,Stephan, Michel,Mohar, Barbara
-
supporting information
p. 1614 - 1617
(2013/06/26)
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- Solution-phase synthesis and evaluation of tetraproline chiral stationary phases
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A protocol was developed for the solution-phase synthesis of multigram amounts of two 9-fluorenylmethoxycarbonyl (Fmoc)-protected tetraproline peptides. These tetraproline peptides were then attached to amino derivatized silica gel. The replacement of the Fmoc group with the trimethylacetyl group lead to two tetraproline chiral stationary phases (CSPs). A comparison of the chromatographic behavior of these two solution-phase-synthesized tetraproline CSPs with that prepared by stepwise solid-phase synthesis revealed that all three had similar chromatographic performance for resolving 53 model analytes. This suggests that the solution-phase synthesis of oligoprolines, which allows for the specific benefits of good batch reproducibility, selector homogeneity, and possibly low cost, is a feasible alternative to the solid-phase synthesis of oligoproline CSPs. Copyright
- Dai, Zhi,Ye, Guozhong,Pittman Jr., Charles U.,Li, Tingyu
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experimental part
p. 329 - 338
(2012/05/20)
-
- Kinetic resolution of secondary alcohols using amidine-based catalysts
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Kinetic resolution of racemic alcohols has been traditionally achieved via enzymatic enantioselective esterification and ester hydrolysis. However, there has long been considerable interest in devising nonenzymatic alternative methods for this transformation. Amidine-based catalysts (ABCs), a new class of enantioselective acyl transfer catalysts developed in our group, have demonstrated, inter alia, high efficacy in the kinetic resolution of benzylic, allylic, and propargylic secondary alcohols and 2-substituted cycloalkanols, and thus provide a viable alternative to enzymes.
- Li, Ximin,Jiang, Hui,Uffman, Eric W.,Guo, Lei,Zhang, Yuhua,Yang, Xing,Birman, Vladimir B.
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experimental part
p. 1722 - 1737
(2012/04/04)
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- A tandem asymmetric synthesis approach for the efficient preparation of enantiomerically pure 9-(hydroxyethyl) anthracene
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A tandem approach for the preparation of gram quantities of enantiomerically pure 9-(hydroxyethyl)-anthracene is presented using an asymmetric reduction followed by kinetic resolution that has potential applicability to other chiral alcohols.
- Ball, Jennifer C.,Brennan, Paul,Elsunaki, Tareg M.,Jaunet, Alexis,Jones, Simon
-
scheme or table
p. 253 - 255
(2011/05/05)
-
- Design, synthesis, and evaluation of a helicenoidal DMAP lewis base catalyst
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The design, synthesis, and study of a helical dialkylaminopyridine Lewis base catalyst is reported. Helical DMAP analogue 4 is based upon a helicenoid structure and displays good to excellent levels of selectivity (S ≤ 116) in the kinetic resolution of chiral secondary alcohols. Catalyst 4 displays excellent reactivity with exceptionally low loadings of 0.05 mol % effecting practical levels of selectivity in kinetic resolutions.(Figure Presented)
- Crittall, Matthew R.,Rzepa, Henry S.,Carbery, David R.
-
supporting information; experimental part
p. 1250 - 1253
(2011/04/25)
-
- OPTICAL-ISOMER SEPARATING AGENT FOR CHROMATOGRAPHY AND PROCESS FOR PRODUCING THE SAME
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A novel optical-isomer separating agent for chromatography is provided which has, as a chiral selector, a macrocyclic amide compound having the ability to function as a chiral shift agent. The optical-isomer separating agent for chromatography is formed by bonding, with a carrier by chemical bonding, a specific ring structure containing an asymmetry recognition site, an amide group as a hydrogen-bond donor site, and a hydrogen-bond acceptor site.
- -
-
Page/Page column 16-17
(2010/12/18)
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- COMPOSITIONS AND METHODS FOR CYCLOFRUCTANS AS SEPARATION AGENTS
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The present invention relates to derivatized cyclofructan compounds, compositions comprising derivatized cyclofructan compounds, and methods of using compositions comprising derivatized cyclofructan compounds for chromatographic separations of chemical species, including enantiomers. Said compositions may comprise a solid support and/or polymers comprising derivatized cyclofructan compounds.
- -
-
Page/Page column 45-49; 55
(2010/12/31)
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- Diastereoselective cycloadditions and transformations of N -alkyl and N -aryl maleimides with chiral 9-anthrylethanol derivatives
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Figure presented. Thermal Diels-Alder reactions of chiral 9-methoxyethyl and 9-hydroxyethyl anthracene have been investigated both experimentally and computationally with a range of N-substituted maleimides. Whereas cycloadditions with 9-methoxyethyl anthracene proceeded with almost complete diastereselectivity, those with 1-anthracene-9-yl-ethanol resulted in essentially no diastereoselectivity. Subsequent regio- and stereoselective transformations with reducing agents and carbon nucleophiles demonstrated the synthetic utility of this methodology, which was applied to the enantioselective synthesis of pyrrolo[2,1-a]isoquinolines and an attempted synthesis of the alkaloid crispine A. Computational studies supported the proposed hypotheses for the stereoselectivity observed in the transformations described.
- Adams, Harry,Elsunaki, Tareg M.,Ojea-Jimenez, Isaac,Jones, Simon,Meijer, Anthony J. H. M.
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experimental part
p. 6252 - 6262
(2010/11/20)
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- Development of new HPLC chiral stationary phases based on native and derivatized cyclofructans
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An unusual class of chiral selectors, cyclofructans, is introduced for the first time as bonded chiral stationary phases. Compared to native cyclofructans (CFs), which have rather limited capabilities as chiral selectors, aliphatic-and aromatic-functionalized CF6s possess unique and very different enantiomeric selectivities. Indeed, they are shown to separate a very broad range of racemic compounds. In particular, aliphatic-derivatized CF6s with a low substitution degree baseline separate all tested chiral primary amines. It appears that partial derivatization on the CF6 molecule disrupts the molecular internal hydrogen bonding, thereby making the core of the molecule more accessible. In contrast, highly aromaticfunctionalized CF6 stationary phases lose most of the enantioselective capabilities toward primary amines, however they gain broad selectivity for most other types of analytes. This class of stationary phases also demonstrates high "loadability" and therefore has great potential for preparative separations. The variations in enantiomeric selectivity often can be correlated with distinct structural features of the selector. The separations occur predominantly in the presence of organic solvents.
- Sun, Ping,Wang, Chunlei,Breitbach, Zachary S.,Zhang, Ying,Armstrong, Daniel W.
-
experimental part
p. 10215 - 10226
(2010/05/01)
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- Benzophenone-derived catalyst with self-adaptation: highly enantioselective hydrogenation irrespective of ketone substrates
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The Ru complex with the tropos benzophenone-derived diphosphine ligand could be chirally controlled to a single chiral conformation instantaneously with a chiral diamine to attain high enantioselectivity in the asymmetric hydrogenation irrespective of ket
- Wakabayashi, Kazuki,Aikawa, Kohsuke,Mikami, Koichi
-
scheme or table
p. 1525 - 1535
(2009/08/17)
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- Palladium-catalyzed enantioselective oxidation of chiral secondary alcohols: Access to both enantiomeric series
-
(Chemical Equation Presented) Rapid resolution: A new catalyst system for the oxidative kinetic resolution of secondary alcohols leads to dramatic rate increases. This system allows the use of a diamine to provide access to either enantiomer of a range of alcohols with good selectivity factors (see scheme). This method has been applied to the formal total synthesis of (-)-amurensinine.
- Ebner, David C.,Trend, Raissa M.,Genet, Cedric,McGrath, Matthew J.,O'Brien, Peter,Stoltz, Brian M.
-
scheme or table
p. 6367 - 6370
(2009/03/11)
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- Stereochemical sensitivity of the human UDP-glucuronosyltransferases 2B7 and 2B17
-
A set of 28 enantiomers comprising rigid and flexible secondary alcohols was synthesized by the asymmetric Corey-Bakshi-Shibata reduction. The enantiomerically pure alcohols were subjected to enzymatic glucuronidation assays employing the human UDP-glucuronosyltransferases (UGTs) 2B7 and 2B17. Both UGTs displayed high levels of stereoselectivity, favoring the conjugation of the (R)-enantiomers over their respective (S)-stereoisomers at eudismic ratios up to 256. The spatial arrangement of the hydroxy group determined the diastereoselectivity of the UGT2B17-catalyzed reaction in agreement with Pfeiffer's rule (eudismic activity quotient = 0.83 ± 0.14). Inhibition studies revealed that the enantiomers had similar affinities toward the enzymes. The diastereoselectivity of the UGT-catalyzed conjugation stemmed, therefore, from the arrangement of the substrates in the catalytic site, rather than from distinct affinities toward the enzymes. Taken together, this study showed that metabolic enzymes that are generally conceived to be rather "flexible" in nature are capable of displaying high levels of chiral distinction.
- Bichlmaier, Ingo,Siiskonen, Antti,Finel, Moshe,Yli-Kauhaluoma, Jari
-
p. 1818 - 1827
(2007/10/03)
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- Mechanistic investigations in diastereoselective Diels-Alder additions of chiral 9-anthrylethanol derivatives
-
The preparation and subsequent Diels-Alder addition reactions of chiral 9-functionalised anthracene derivatives have been investigated. 9-(1-Methoxyethyl)anthracene undergoes highly diastereoselective (>95:5) thermal and photoinduced Diels-Alder additions with maleic anhydride and N-methylmaleimide. The corresponding reactions of 1-anthracen-9-ylethanol occur with the reverse sense of selectivity for additions with maleic anhydride with a corresponding increase in the reaction rate. The origins of this selectivity have been proposed to lie in hydrogen-bonding effects. The stereochemical outcome of the Diels-Alder additions has been determined from single X-ray crystallography of adducts 5 and 7. Solvent effects on the diastereoselectivity of these reactions have also been observed.
- Atherton, J. C. Christian,Jones, Simon
-
p. 2166 - 2173
(2007/10/03)
-
- Establishing cleavage conditions for an anthracene chiral auxiliary using a photochemical retro Diels-Alder reaction
-
Photochemical Diels-Alder additions of chiral 9-anthranyl ethanol derivatives have been conducted giving rise to addition adducts in reasonable yield and excellent diastereoselectivity. Thermal and photochemical retro Diels-Alder additions have also been
- Atherton, J.C.Christian,Jones, Simon
-
p. 9097 - 9100
(2007/10/03)
-
- Highly diastereoselective photochemical Diels-Alder reactions: Towards the development of a photoactivated chiral auxiliary
-
Photochemical Diels-Alder additions of maleic anhydride to a homochiral anthracene derivative occur with excellent diastereoselectivity (>95:5) and faster than the corresponding thermal reactions.
- Jones, Simon,Atherton
-
p. 1117 - 1119
(2007/10/03)
-
- Assignment of the Absolute Configuration of α-Chiral Carboxylic Acids by H NMR Spectroscopy
-
The prediction of the absolute configuration of α-chiral carboxylic acids from the 1H NMR spectra of their esters with (R)- and (S)-ethyl 2-hydroxy-2-(9-anthryl) acetate [(R)- and (S)-9-AHA, 5] is discussed. Low-temperature NMR experiments, MM, semiempirical, and aromatic shielding effect calculations allowed the identification of the main conformers and showed that, in all esters studied, conformer ap is the most stable. A simple model for the assignment of the absolute configuration from NMR data is presented, and its reliability is corroborated with acids 6-31 of known absolute configuration. In addition to 5, other auxiliary reagents with open (32-38) and cyclic (39-42) structures have also been studied. trans-(+)- and (-)-2-phenyl-1-cyclohexanol (41) was found to be particularly efficient and produced ΔδRS values similar to those of 5.
- Ferreiro, Maria J.,Latypov, Shamil K.,Quinoa, Emilio,Riguera, Ricardo
-
p. 2658 - 2666
(2007/10/03)
-
- Stereoselective diels-alder reactions of chiral anthracenes
-
(equation presentd) Various chiral (9-anthryl)carbinol templates undergo Diels-Alder cycloadditions with a variety of symmetric and nonsymmetric dienophiles with excellent π-facial selectivity and regioselectivity, under both thermal and Lewis acid cataly
- Sanyal, Amitav,Snyder, John K.
-
p. 2527 - 2530
(2007/10/03)
-
- The scope of catalytic asymmetric hydroboration/oxidation with rhodium complexes of 1,1'-(2-diarylphosphino-1-naphthyl)isoquinolines
-
Preformed cationic Rh complexes of the title ligands are effective for the asymmetric hydroboration/oxidation of vinylarenes at ambient temperature. These vinylarenes may carry E- or Z-β substituents but not a substituents. Enantiomer excesses of up to 97% can be obtained in the most favourable cases. The enantioselectivity is moderately sensitive to the structure of the ligand: the difurylphosphino ligand gave superior results for electron-poor styrenes and the diphenylphosphino ligand the best results for electron-rich reactants. Mechanistic aspects are discussed.
- Doucet, Henri,Fernandez, Elena,Layzell, Timothy P.,Brown, John M.
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p. 1320 - 1330
(2007/10/03)
-
- Charge delocalization in persistent benz[a]anthracenium cations bah+ and related α-carbocations/carboxonium ions: modeling epoxide ring opening in potent carcinogens
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Parent BA 1 protonates at C-7/C-12 to give 1H+ and laH+ in 3:1 ratio which remains unaffected by variation in temperature and the superacid system. Increasing steric crowding at the bayregion by introduction of a methyl at C-l (1-MBA) changes the ratio of C-7/C-12 protonated arenium ions 2H+/2aH+ to 10:1. The highly potent 7,12-dimethylbenz[a]anthracene, 7,12-DMBA, gives a 1:1 mixture of the two ipso-protonated cations 3aH+/3H+ whose composition changes to 50:1 overtime in favor of 3aH+ (ipso-attack at bay-region), showing it to be the thermodynamic cation. 3-Methylcholanthrene, 3MC, is exclusively protonated at C-6 (→4aH+). Cation 5+ (a simplified model for bay-region epoxide ring opening) is cleanly formed via its carbinol 5-OH with FSO3H/ SO2C1F. Ketone 6 is O-protonated in TFAH and in TFAH/H2SO4 to give the bay-region carboxonium ion 6H+; its diprotonation in FSO3H·SbFs (4:1)/SO2C1F gave the first example of the oxoniumarenium dication 6H22+. α-BA-substituted secondary carbocation 7+ and the carboxonium ion 8H+ were generated to probe charge delocalization into the α-BA moiety via C-7. To gauge the importance of the benz[α] ring and for comparison, the anthracene-substituted carbocations 9+ and carboxonium ion 10H+ were generated and studied. Charge delocalization pathways into the PAH periphery are evaluated on the basis of Δδ13C values. AMI was used as a complementary tool for qualitative comparison with experiment. The resulting arenium ions and benzylic carbocations exhibit strong anthracenium ion character emphasizing the importance of an electrondeficient anthracene moiety. The present study constitutes the first direct investigation of carbocations in the BA series, whose bay-region and K-region diol epoxides are considered the ultimate carcinogens en route to PAH-DNA adduct formation.
- Laali, Kenneth K.,Tanaka, Mutsuo
-
p. 7280 - 7285
(2007/10/03)
-
- Preparation of 1-(9-anthryl)-ethanol and 9-anthryloxirane via catalytic enantioselective reduction of prochiral 9-anthryl ketones
-
Enantioselective reduction of prochiral 9-anthryl ketones to the corresponding chiral alcohols proceeds with high enantiomeric excess. The chiral alcohol 1-(9-anthryl)-2-bromo-ethanol can be converted to the corresponding chiral oxirane.
- Reiners,Martens
-
-
- [(3-dimethylamino)propyl]dimethylaluminum: A convenient reagent for methylation and ethynylation of carbonyl compounds
-
At 60-80°C the title compound methylates a variety of mono- and diketones. Aromatic aldehydes undergo simple methylation by the reagent only after initial treatment with an equivalent amount of AlCl3. Upon reaction of Me2Al(CH2)3NMe2 with terminal acetylenes the aluminum complex is converted into a carbonyl-alkynylation reagent.
- Baidossi, Wael,Rosenfeld, Ayelet,Wassermann, Brigit C.,Schutte, Stefan,Schumann, Herbert,Blum, Jochanan
-
p. 1127 - 1130
(2007/10/03)
-
- Magnetic Resonance Study of Diastereomeric Interactions of Nitroaromatic Sulfoxides with Alcohols in Solution
-
The synthesis of optically active (1R,2R)- and(1S,2R)-2-deutero-2,3-dihydro-2-methyl-6-nitrobenzothiophene-1-oxide (3 and 4) is described.Several racemic aryl methyl carbinols in the presence of 3 or 4 give different chemical shifts for enantiomeric CH, CH3 and OH protons.These chemical shift differences are larger than those observed in analogous sulfoxide-alcohol pairs without nitro groups.Quinine and cinchonidine cause observable non-equivalence of methylene and aromatic protons in racemic 4.The magnitude of the diastereomeric shift difference is sensitive to temperature, solvent, concentration, nature of the ? system and steric effects.
- Sweeting, Linda M.,Anet, Frank A. L.
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p. 539 - 542
(2007/10/02)
-
- RESTRICTED ROTATION INVOLVING THE TETRAHEDRAL CARBON. L. ROTAMER DISTRIBUTIONS AND ROTATIONAL BARRIERS IN SOME 9-(1-METHOXYETHYL)TRIPTYCENE DERIVATIVES.
-
1,4-Dimethyl- and 1,2,3,4-tetrahalo-9-(1-methoxyethyl)triptycenes were synthesized by reactions of 9-(1-methoxyethyl)anthracene with appropriate benzynes. Rotamer distributions and rotational barriers about the bridgehead-to-substituent bond were studied by NMR spectroscopy. Rotamer distributions are governed mainly by the steric effect; the major rotamer is assigned to sc*(S*), the minor one to ap, and the third one found only in the tetrafluoro derivative to sc*(R*). *). Rotational barriers are 21-23 kcal mol** minus **1 which are slightly lower than those for the corresponding 9-isopropyltriptycenes.
- Tanaka,Yamamoto,Oki
-
p. 3023 - 3027
(2007/10/02)
-