- Stereoselectivity in intramolecular diene cyclozirconation: A combined experimental and theoretical approach
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Intramolecular diene cyclozirconation (1 → 2 + 3 → 4) can be highly diastereoselective (97:3 trans/cis for 4). It is suggested that the cis and trans diastereomers of the zirconacycle are equilibrating under the conditions of the reaction, and that the observed diastereomeric preference of 4 reflects the relative stability of the two diastereomeric zirconacycles. Results for the intramolecular cyclozirconation of two other dienes, 8 and 14, as well as for the "heterodiene" N,N-diallylaniline are also reported. Computational results at the molecular mechanics, semiempirical molecular orbital ZINDO and nonlocal density functional theory levels are used to explain the observed stereochemistry in terms of thermodynamic and kinetic control.
- Taber, Douglass F.,Louey, James P.,Wang, Yanong,Nugent, William A.,Dixon, David A.,Harlow, Richard L.
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Read Online
- Development of effective bidentate diphosphine ligands of ruthenium catalysts toward practical hydrogenation of carboxylic acids
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Hydrogenation of carboxylic acids (CAs) to alcohols represents one of the most ideal reduction methods for utilizing abundant CAs as alternative carbon and energy sources. However, systematic studies on the effects of metal-to-ligand relationships on the catalytic activity of metal complex catalysts are scarce. We previously demonstrated a rational methodology for CA hydrogenation, in which CA-derived cationic metal carboxylate [(PP)M(OCOR)]+ (M = Ru and Re; P = one P coordination) served as the catalyst prototype for CA self-induced CA hydrogenation. Herein, we report systematic trial- and-error studies on how we could achieve higher catalytic activity by modifying the structure of bidentate diphosphine (PP) ligands of molecular Ru catalysts. Carbon chains connecting two P atoms as well as Ar groups substituted on the P atoms of PP ligands were intensively varied, and the induction of active Ru catalysts from precatalyst Ru(acac)3 was surveyed extensively. As a result, the activity and durability of the (PP)Ru catalyst substantially increased compared to those of other molecular Ru catalyst systems, including our original Ru catalysts. The results validate our approach for improving the catalyst performance, which would benefit further advancement of CA self-induced CA hydrogenation.
- Saito, Susumu,Wen, Ke,Yoshioka, Shota
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supporting information
p. 1510 - 1524
(2021/06/18)
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- Epimerization of Tertiary Carbon Centers via Reversible Radical Cleavage of Unactivated C(sp3)-H Bonds
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Reversible cleavage of C(sp3)-H bonds can enable racemization or epimerization, offering a valuable tool to edit the stereochemistry of organic compounds. While epimerization reactions operating via cleavage of acidic C(sp3)-H bonds, such as the Cα-H of carbonyl compounds, have been widely used in organic synthesis and enzyme-catalyzed biosynthesis, epimerization of tertiary carbons bearing a nonacidic C(sp3)-H bond is much more challenging with few practical methods available. Herein, we report the first synthetically useful protocol for the epimerization of tertiary carbons via reversible radical cleavage of unactivated C(sp3)-H bonds with hypervalent iodine reagent benziodoxole azide and H2O under mild conditions. These reactions exhibit excellent reactivity and selectivity for unactivated 3° C-H bonds of various cycloalkanes and offer a powerful strategy for editing the stereochemical configurations of carbon scaffolds intractable to conventional methods. Mechanistic study suggests that the unique ability of N3? to serve as a catalytic H atom shuttle is critical to reversibly break and reform 3° C-H bonds with high efficiency and selectivity.
- Wang, Yaxin,Hu, Xiafei,Morales-Rivera, Cristian A.,Li, Guo-Xing,Huang, Xin,He, Gang,Liu, Peng,Chen, Gong
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supporting information
p. 9678 - 9684
(2018/07/21)
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- Simple Preparation of Rhodococcus erythropolis DSM 44534 as Biocatalyst to Oxidize Diols into the Optically Active Lactones
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In the current study, we present a green toolbox to produce ecological compounds like lactone moiety. Rhodococcus erythropolis DSM 44534 cells have been used to oxidize both decane-1,4-diol (2a) and decane-1,5-diol (3a) into the corresponding γ- (2b) and δ-decalactones (3b) with yield of 80% and enantiomeric excess (ee)?=?75% and ee?=?90%, respectively. Among oxidation of meso diols, (?)-(1S,5R)-cis-3-oxabicyclo[4.3.0]non-7-en-2-one (5a) with 56% yield and ee?=?76% as well as (?)-(2R,3S)-cis-endo-3-oxabicyclo[2.2.1]dec-7-en-2-one (6a) with 100% yield and ee?=?90% were formed. It is worth mentioning that R. erythropolis DSM 44534 grew in a mineral medium containing ethanol as the sole source of energy and carbon Chirality 28:623–627, 2016.
- Martinez-Rojas, Enriqueta,Olejniczak, Teresa,Neumann, Konrad,Garbe, Leif-Alexander,Boraty?ski, Filip
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p. 623 - 627
(2016/10/11)
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- Microbial alcohol dehydrogenase screening for enantiopure lactone synthesis: Down-stream process from microtiter plate to bench bioreactor
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One-pot conversion with whole cells of bacteria was performed for biooxidation of meso monocyclic (3a-b) and bicyclic diols (3c-e) into corresponding chiral lactones of bicyclo[4.3.0]nonane structure (2a-b) as well as exo- and endo-bridged lactones with the structure of [2.2.1] (3c-d) and [2.2.2] (3e). Micrococcus sp. DSM 30771 was selected as biocatalyst with significant alcohol dehydrogenase activity. Among tested strains, microbial oxidation of meso diols 3a-e catalyzed by Micrococcus sp. afforded enantiomerically pure ((+)-(2S,3R)-2c (ee = 99%), (+)-(2S,3R)-2e (ee = 99%)) or enriched ((+)-(1S,5R)-2a (ee = 90%), (-)-(1S,5R)-2b (ee = 86%), (+)-(2S,3R)-2d (ee = 80%)) lactone moieties. Comparative study with respect to microbial cultivation as well as biooxidation was undertaken to verify agreement of secondary metabolite biosynthesis in different scales: from MTP (4 mL), across shake flask (100 mL) till bioreactor (4 L). The results from biotransformations showed quite similar dependence in oxidation of all substrates 3a-e in MTP and flasks as well, thereby confirmed the validity and reasonable approach of using MTP for preliminary studies.
- Boratyński,Pannek,Walczak,Janik-Polanowicz,Huszcza,Szczepańska,Martinez-Rojas,Olejniczak
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p. 1637 - 1646
(2015/02/05)
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- Discovery of octahydroindenes as PAR1 antagonists
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Octahydroindene was identified as a novel scaffold for protease activated receptor 1 (PAR1) antagonists. Herein, the 2-position (C2) was explored for structure-activity relationship (SAR) studies. Compounds 14, 19, and 23b showed IC50 values of 1.3, 8.6, and 2.7 nM in a PAR1 radioligand binding assay, respectively, and their inhibitory activities on platelet activation were comparable to that of vorapaxar in a platelet rich plasma (PRP) aggregation assay. This series of compounds showed high potency and no significant cytotoxicity; however, the compounds were metabolically unstable in both human and rat liver microsomes. Current research efforts are focused on optimizing the compounds to improve metabolic stability and physicochemical properties as well as potency.
- Lee, Sunkyung,Song, Jong-Hwan,Park, Chul Min,Kim, Jin-Seok,Jeong, Ji-Hye,Cho, Woo-Young,Lim, Dong-Chul
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supporting information
p. 1054 - 1058
(2013/12/04)
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- Fungistatic activity of bicyclo[4.3.0]-γ-lactones
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Five optically active and sixteen racemic lactones (nine of them new) of bicyclo[4.3.0]nonane structure were synthesized. IC50 values for the following phytopathogens were determined: Aspergillus ochraceus AM 456, Fusarium culmorum AM 282, Fusarium oxysporum AM 13, Fusarium tricinctum AM 16. Effect of compound structures, especially stereogenic centers, on fungistatic activity has been discussed. The highest fungistatic activity was observed for trans-7,8-dibromo-cis-3-oxabicyclo[4.3.0]nonan-2-one (3c), IC50 = 30.1 μg/mL (0.10 μM/mL), and cis-7,8-epoxy-cis-3-oxabicyclo[4.3.0]nonan-2- one (3b), IC50 = 72.2 μg/mL (0.47 μM/mL), toward F. oxysporum AM 13.
- Olejniczak, Teresa,Boratynski, Filip,Bialonska, Agata
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scheme or table
p. 6071 - 6081
(2012/02/03)
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- [6+5] FUSED BICYCLES AS A THROMBIN ANTAGONIST, PROCESS FOR PREPARATION THEREOF AND PHARMACEUTICAL COMPOSITIONS CONTAINING THE BICYCLES
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The present invention relates to the new [6+5] fused bicycle derivatives, pharmaceutically acceptable salts or isomers thereof, processes for preparing the same, and pharmaceutical compositions comprising the same. The [6+5] fused bicycle derivatives can antagonize the thrombin receptor and thus may be effectively used for the treatment and prevention of thrombus, platelet aggregation, atherosclerosis, restenosis, blood coagulation, hypertension, arrhythmia, angina pectoris, heart failure, inflammation and cancer when used alone or with other cardiovascular agents.
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Page/Page column 40
(2012/01/14)
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- Characterization and alkane oxidation activity of a diastereopure seven-coordinate iron(III) alkylperoxo complex
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Spectroscopic characterization and alkane oxidation studies of a diastereopure seven-coordinate high-spin iron(iii) alkylperoxo complex based on the chiral N,N′,N-bis(l-prolinate)pyridine ligand Py(ProMe)2 (1) are reported. The Royal Society of Chemistry 2007.
- Gosiewska, Silvia,Permentier, Hjalmar P.,Bruins, Andries P.,Van Koten, Gerard,Gebbink, Robertus J. M. Klein
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p. 3365 - 3368
(2008/02/10)
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- Dihalocarbene insertion reactions into C-H bonds of compounds containing small rings: Mechanisms and regio- and stereoselectivities
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(Chemical Equation Presented) Novel insertion reactions of dichloro- and dibromocarbene into carbon-hydrogen bonds adjacent to cyclopropane rings are reported. It is found that the predominant isomers formed in the reactions with bicyclo[4.1.0]heptane result from insertion into the endo carbon-hydrogen bonds alpha to the three-membered ring. In the reactions of bicyclo[3.1.0]hexane, however, the exo dihalocarbene insertion products are formed as the major isomers. In some compounds cyclopropane rings "activate" adjacent carbon-hydrogen bonds, whereas other systems containing three-membered rings do not. Moreover, the influence of various substituents (methyl, geminal dimethyl, phenyl, methoxy, and ethoxy) attached to bicyclo-[3.1.0]hexane and bicyclo[4.1.0]heptane in dihalocarbene reactions has been studied. The findings can be explained by the concept of maximum orbital overlaps of Walsh orbitals of the cyclopropane rings and the α carbon-hydrogen bonds. In stark contrast, selective insertion into the tertiary carbon-hydrogen bonds of the cyclobutane ring in bicyclo[4.2.0]octane is observed.
- Brinker, Udo H.,Lin, Guoying,Xu, Linxiao,Smith, William B.,Mieusset, Jean-Luc
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p. 8434 - 8451
(2008/02/13)
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- Ruthenium(salen)-catalyzed aerobic oxidative desymmetrizatin of meso-diols and its kinetics
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Chiral (nitrosyl)ruthenium(salen) complexes were found to be efficient catalysts for aerobic oxidative desymmetrization of meso-diols under photoirradiation to give optically active tactols. The scope of the applicability of this reaction ranges widely from acyclic diols to mono-cyclic diols, although fine ligand-tuning of the ruthenium(salen) complexes was required to attain high enantioselectivity (up to 93% ee). In particular, the nature of the apical ligand was found to affect not only enantioselectivity but also kinetics of the desymmetrization reaction. Spectroscopic analysis of the oxidation disclosed that irradiation of visible light is indispensable not only for dissociation of the nitrosyl ligand but also for single electron transfer from the alcohol-bound ruthenium ion to dioxygen.
- Shimizu, Hideki,Onitsuka, Satoaki,Egami, Hiromichi,Katsuki, Tsutomu
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p. 5396 - 5413
(2007/10/03)
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- Efficient desymmetrization of meso-cis-1,2-cyclohexanedimethanol with differentiation between diastereotopic and enentiotopic C-H bonds by (-)- sparteine-mediated deprotonation
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The deprotonation of a dicarbamate prepared from cis-1,2- cyclohexanedimethanol by sec-butyllithium/(-)-sparteine proceeds with efficient selection between the enantiotopic branches and their diastereotopic protons with high preference for the pro-S proto
- Van Bebber, Jan,Ahrens, Hartmut,Froehlich, Roland,Hoppe, Dieter
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p. 1905 - 1916
(2007/10/03)
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- (2-Vinylcyclopropyl)carbenes. More stepwise mechanisms for ring-expansion
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A simple vinyl group is sufficient to induce a stepwise mechanism for the ring expansion of cyclopropylcarbenes.
- Cummins, Jordan M.,Pelczer, Istvan,Jones Jr., Maitland
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p. 7595 - 7599
(2007/10/03)
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- Evidence for 2-Hexene-1,6-diyl Diradicals Accompanying the Concerted Diels-Alder Cycloaddition of Acrylonitrile with Nonpolar 1,3-Dienes
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The spontaneous reactions of a series of alkyl 1,3-dienes with acrylonitrile (AN) were investigated.Reproducible spontaneous copolymerizations were shown to compete with the expected concerted cycloadditions.For dienes which exist in s-cis/s-trans equilibrium, both copolymer and cycloadduct are formed.Kinetic measurements show that the alternating copolymerization and cycloaddition are two independent paralell second order reactions.With 1,3-cyclohexadiene and 1,2-dimethylenecyclohexane, for which s-gauche is in equilibrium with s-cis, copolymerization still competes with cycloaddition.The s-trans-locked verbenene forms only copolymer, while s-cis-locked cyclopentadiene and 1,2-dimethylenecyclopentane form only cycloadduct rapidly.Our explanation involves a 2-hexene-1,6-diradical, formed by combination between the terminal carbons of the s-gauche or s-trans diene and acrylonitrile.This does not cyclize but initiates copolymerization.Competitively s-cis conformer undergoes classical concerted addition.
- Li, Yufei,Padias, Anne Buyle,Hall, H. K.
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p. 7049 - 7058
(2007/10/02)
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- The Stereochemistry of Organometallic Compounds. XXXVIII. Regio- and Stereo-control in the Rhodium-Catalysed Hydroformylation of Some Alkenyl Phosphites
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Excellent regiocontrol is achieved in the rhodium-catalysed hydroformylation of some alkenyl phosphites, and good stereocontrol is obtained in the hydroformylation of some cyclohexenyl phosphites.The stereochemical results have implications for the mechanism of these rhodium-catalysed reactions.
- Jackson, W. Roy,Moffat, Mark R.,Perlmutter, Patrick,Tasdelen, E. Elizabeth
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p. 823 - 834
(2007/10/02)
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- Chelation Control by Phosphite Esters in Rhodium Catalysed Hydroformylation
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Phosphite esters can be used to give excellent regiocontrol in rhodium catalysed hydroformylation reactions of alkenes and in addition excellent stereocontrol in the reactions of some cyclohexenyl phosphites.
- Jackson, W. Roy,Perlmutter, Patrick,Tasdelen, E. Elizabeth
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p. 763 - 764
(2007/10/02)
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- Aqueous Cycloaddition using Glyco-organic Substrates. Facial Stereoselectivity in Diels-Alder Reactions of a Chiral Diene derived from D-Glyceraldehyde
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The preparation of a new chiral, water-soluble E-diene, which could be considered as the simplest diene obtainable from the simplest sugar, is described, along with its use in cycloaddition with acrylaldehyde.Water, as the solvent, enhanced the rate of the Diels-Alder reaction, promoted complete regio- and endo-selectivity, and improved a like (anti) facial selectivity, compared with the results obtained with organic solvents.
- Lubineau, Andre,Auge, Jacques,Lubin, Nadege
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p. 3011 - 3015
(2007/10/02)
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- Enantioselective hydrolysis of cis-1,2-diacetoxycycloalkanedimethanols: enzymatic preparation of chiral building blocks from prochiral meso-substrates.
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The enzymatic hydrolysis of the prochiral title compounds 1a-f in presence of porcine liver esterase (PLE) and lipase from porcine pancreas (PPL) was studied, resulting in the preparation of the chiral monoacetates 2b-f with high (72-99percente.e.) enantiomeric purities.
- Laumen, Kurt,Schneider, Manfred
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p. 2073 - 2076
(2007/10/02)
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- Enzymes in Organic Synthesis. 24. Preparations of Enantiomerically Pure Chiral Lactones via Stereospecific Horse Liver Alcohol Dehydrogenase Catalyzed Oxidations of Monocyclic Meso Diols
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Preparative-scale horse liver alcohol dehydrogenase catalyzed oxidation of monocyclic meso diols provides a direct and convenient one-step route to a broad range of chiral γ-lactones of value as synthons in asymmetric synthesis.The general applicability of the method is demonstrated by oxidations of cis-1,2-bis(hydroxymethyl) substrates of the cyclohexyl, cyclohexenyl, cyclopentyl, cyclobutyl, cyclopropyl, and dimethylcyclopropyl series.For each diol, oxidation of the hydroxymethyl group attached to the S chiral center occurs exclusively, and the pure γ-lactone products are isolated in high (68-90percent) yields and of 100percent ee.In contrast, the enzyme does not exhibit significant enantiomeric selectivity in its catalysis of oxidations of the corresponding racemic trans diols.The stereospecificities observed, or lack thereof, are as predicted by the active-site model.
- Jakovac, Ignac J.,Goodbrand, H. Bruce,Lok, Kar P.,Jones, J. Bryan
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p. 4659 - 4665
(2007/10/02)
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- Conformational Equilibrium in 8-Methyl-cis-2-thiahydrindane and 8-Methyl-cis-2-oxahydrindane by 13C NMR Spectroscopy
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The preferred conformation of 8-methyl-cis-thiahydrindane has been both estimated by 13C NMR chemical shifts and determined by low temperature 13C NMR spectroscopy to be the conformer with the methyl group equatorial with respect to the cyclohexane ring.This result is in disagreement with the interpretation of the temperature dependence of the CD spectra of (+) and (-) 8-methyl-cis-2-thiahydrindane, whereby the conformation with the methyl group axial with respect to the cyclohexane ring was claimed to be the preferred conformation.The preferred conformation of the related oxygen heterocycle, 8-methyl-cis-2-oxahydrindane, has been estimated by 13C NMR chemical shifts to be the conformer with the methyl group axial with respect to the cyclohexane ring.Possible reasons for these observations are discussed.
- Willer, Rodney L.
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p. 261 - 265
(2007/10/02)
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- Reactions of α-Halotetrahydrothiophene 1,1-Dioxides with Strong Bases
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This article describes the halogenated sulfones 2, 3, 7, 11, 16 and 18 obtained from the hitherto unknown intermediates 4, 5, 6 and 8, 9, 10 and from 14, 15.An account is given of Ramberg-Baecklund-type reactions undergone by the α-halogenated cyclic sulfones 2a and 7 with bases at high temperature.
- Neidlein, Richard,Doerr, Henning
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p. 1540 - 1548
(2007/10/02)
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