- Electro-mediated PhotoRedox Catalysis for Selective C(sp3)–O Cleavages of Phosphinated Alcohols to Carbanions
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We report a novel example of electro-mediated photoredox catalysis (e-PRC) in the reductive cleavage of C(sp3)?O bonds of phosphinated alcohols to alkyl carbanions. As well as deoxygenations, olefinations are reported which are E-selective and can be made Z-selective in a tandem reduction/photosensitization process where both steps are photoelectrochemically promoted. Spectroscopy, computation, and catalyst structural variations reveal that our new naphthalene monoimide-type catalyst allows for an intimate dispersive precomplexation of its radical anion form with the phosphinate substrate, facilitating a reactivity-determining C(sp3)?O cleavage. Surprisingly and in contrast to previously reported photoexcited radical anion chemistries, our conditions tolerate aryl chlorides/bromides and do not give rise to Birch-type reductions.
- Barham, Joshua P.,K?nig, Burkhard,Karl, Tobias A.,Reiter, Sebastian,Tian, Xianhai,Yakubov, Shahboz,de Vivie-Riedle, Regina
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supporting information
p. 20817 - 20825
(2021/08/18)
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- Enantioselective Tail-to-Head Cyclizations Catalyzed by Dual-Hydrogen-Bond Donors
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Chiral urea derivatives are shown to catalyze enantioselective tail-to-head cyclization reactions of neryl chloride analogues. Experimental data are consistent with a mechanism in which ?-participation by the nucleophilic olefin facilitates chloride ionization and thereby circumvents simple elimination pathways. Kinetic and computational studies support a cooperative mode of catalysis wherein two molecules of the urea catalyst engage the substrate and induce enantioselectivity through selective transition state stabilization.
- Kutateladze, Dennis A.,Strassfeld, Daniel A.,Jacobsen, Eric N.
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p. 6951 - 6956
(2020/05/19)
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- Upcycling a plastic cup: One-pot synthesis of lactate containing metal organic frameworks from polylactic acid
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Waste PLA can be upcycled to metal organic frameworks of potential high value in a one-pot synthesis scheme, where PLA depolymerisation occurs in situ. Three homochiral lactate based frameworks were successfully synthesised and characterised from PLA as a feed source, including ZnBLD. The chiral separation ability of ZnBLD was maintained.
- Slater, Benjamin,Wong, So-On,Duckworth, Andrew,White, Andrew J. P.,Hill, Matthew R.,Ladewig, Bradley P.
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supporting information
p. 7319 - 7322
(2019/06/27)
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- Converting S-limonene synthase to pinene or phellandrene synthases reveals the plasticity of the active site
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S-limonene synthase is a model monoterpene synthase that cyclizes geranyl pyrophosphate (GPP) to form S-limonene. It is a relatively specific enzyme as the majority of its products are composed of limonene. In this study, we converted it to pinene or phellandrene synthases after introducing N345A/L423A/S454A or N345I mutations. Further studies on N345 suggest the polarity of this residue plays a critical role in limonene production by stabilizing the terpinyl cation intermediate. If it is mutated to a non-polar residue, further cyclization or hydride shifts occurs so the carbocation migrates towards the pyrophosphate, leading to the production of pinene or phellandrene. On the other hand, mutant enzymes that still possess a polar residue at this position produce limonene as the major product. N345 is not the only polar residue that may stabilize the terpinyl cation because it is not strictly conserved among limonene synthases across species and there are also several other polar residues in this area. These residues could form a “polar pocket” that may collectively play this stabilizing role. Our study provides important insights into the catalytic mechanism of limonene synthases. Furthermore, it also has wider implications on the evolution of terpene synthases.
- Xu, Jinkun,Ai, Ying,Wang, Jianhui,Xu, Jingwei,Zhang, Yongkang,Yang, Dong
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- Photocatalytic Transfer Hydrogenolysis of Allylic Alcohols on Pd/TiO2: A Shortcut to (S)-(+)-Lavandulol
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We report herein a regio- and stereoselective photocatalytic hydrogenolysis of allylic alcohols to form unsaturated hydrocarbons employing a palladium(II)-loaded titanium oxide; the reaction proceeds at room temperature under light irradiation without stoichiometric generation of salt wastes. Olefin and saturated alcohol moieties tolerated the reaction conditions. Hydrogen atoms were selectively incorporated into less sterically congested carbons of the allylic functionalities. This protocol allowed a short-step synthesis of (S)-(+)-lavandulol from (R)-(?)-carvone by avoiding otherwise necessary protection/deprotection steps.
- Takada, Yuki,Caner, Joaquim,Kaliyamoorthy, Selvam,Naka, Hiroshi,Saito, Susumu
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supporting information
p. 18025 - 18032
(2017/12/08)
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- Isotope sensitive branching and kinetic isotope effects to analyse multiproduct terpenoid synthases from Zea mays
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Multiproduct terpene synthases TPS4-B73 and TPS5-Delprim from Zea mays exhibit isotopically sensitive branching in the formation of mono- and sesquiterpene volatiles. The impact of the kinetic isotope effects and the stabilization of the reactive intermediates by hyperconjugation along with the shift of products from alkenes to alcohols are discussed.
- Gatto, Nathalie,Vattekkatte, Abith,K?llner, Tobias,Degenhardt, J?rg,Gershenzon, Jonathan,Boland, Wilhelm
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supporting information
p. 3797 - 3800
(2015/03/30)
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- Metal-organic framework Co(D-cam)1/2(bdc)1/2(tmdpy) for improved enantioseparations on a chiral cyclodextrin stationary phase in gas chromatography
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Initial efforts to combine a chiral metal-organic framework (MOF), Co(D-Cam)1/2(bdc)1/2(tmdpy) (D-Cam=D-camphoric acid, bdc=1,4-benzenedicarboxylic acid, tmdpy=4,4′-trimethylenedipyridine), with peramylated β-cyclodextrins to investigate whether the use of a MOF can enhance enantioseparations on a cyclodextrin stationary phase are reported. Compared with columns of peramylated β-cyclodextrin incorporated in a MOF containing sodium chloride, the column of peramylated β-cyclodextrin+MOF shows excellent selectivity for the recognition of racemates, and higher resolutions are achieved on the peramylated β-cyclodextrin+MOF stationary phase. Experimental results indicate that the use of Co(D-Cam) 1/2(bdc)1/2(tmdpy) can improve enantioseparations on peramylated β-cyclodextrins. This is the first report that chiral MOFs can improve enantioseparations on a chiral stationary phase for chromatography. Copyright
- Liu, Hong,Xie, Sheng-Ming,Ai, Ping,Zhang, Jun-Hui,Zhang, Mei,Yuan, Li-Ming
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p. 1103 - 1108
(2014/11/07)
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- Oxidation of α-pinene by atmospheric oxygen in the supercritical CO2-ethyl acetate system in the presence of Co(II) complexes
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The reactivity of monoterpene α-pinene in a flow reactor in the presence of cobalt catalyst in a complex supercritical solvent consisting of CO2 and ethyl acetate is studied over the temperature range of 190-320°C and a pressure range of 110-125 atm. It was found that the main isomerization products include compounds with bicyclo[2.2.1]heptane and p-menthane backbones; the reaction is accompanied by partial racemization. The formation of oxidation products is observed in the presence of air, with epoxydation rather than allylic oxidation being the predominant process at the first stage. The oxidized products (campholenic aldehyde, verbenone, pinocamphone) are shown to be formed with a high enantioselectivity; the formation of acetoxylation products is observed at temperatures above 200°C.
- Anikeev,Ilina,Kurbakova,Nefedov,Volcho,Salakhutdinov
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experimental part
p. 190 - 195
(2012/03/12)
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- Comparative thermolysis of β-and α-pinenes in supercritical ethanol: The reaction characterization and enantiomeric ratios of products
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The thermolysis of β-pinene and the co-thermolysis of an equimolar mixture of β-and α-pinenes in supercritical ethanol were carried out. The reaction of β-pinene affords β-myrcene as the major product (>70%). Considerable differences in the temperature dependence of the reaction rate were revealed for the transformations of β-pinene into β-myrcene and of α-pinene into limonene. The pre-exponential factors and the activation energies were calculated. The enantiomeric ratios of the thermolysis products of β-and α-pinenes and limonene were estimated. The starting monoterpenes do not undergo racemization during thermolysis. The thermolysis of enantiomerically pure α-pinene affords racemic (±)-limonene, whereas (-)-β-pinene gives (-)-limonene. The enantiomeric ratio in the latter remains equal to the enantiomeric purity of the starting β-pinene.
- Chibiryaev,Yermakova,Kozhevnikov,Sal'nikova,Anikeev
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p. 1234 - 1238
(2008/09/18)
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- The kinetics, stereochemistry, and deuterium isotope effects in the α-pinene pyrolysis. Evidence for incursion of multiple conformations of a diradical
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Pyrolysis of optically active α-pinene gave 95% racemic limonene (dipentene), alloocimine, racemic α-pinene, α-pyronene. Activation parameters are reported. Pyrolysis of (S) syn-6-trideuteriomethyl α-pinene at 256.7°C for 2400s gave dipentene with twice as much deuterium as hydrogen transfer with kH/kD=1.49 and alloocimine with a Z and E trideuteriomethyl ratio of ca. 5 with kH/kD=0.89. The isotope effect on loss of starting material was 1.16. Separation of the enantiomers of α-pinene from 3600s pyrolyses at 256.7°C followed by NMR analysis revealed that the ratio of the R-syn to R-anti to S-anti isomers is 4.6:3.7:1 at roughly two half-lives. Kinetic analysis reveals that the previously proposed mechanism for all conversions involving slow interconversion of two diradicals with Cs symmetry is not consistent with the distribution of the ??-pinene isomers, particularly the formation of more suprafacial-retention product (R-anti) than bond-rotated isomer (S-anti). Inclusion of another Cs species (ignoring the deuteriums) that would be intermediate between the originally proposed Cs species, appears more consistent with the observations.
- Gajewski, Joseph J,Kuchuk, Ilya,Hawkins, Christopher,Stine, Robert
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p. 6943 - 6950
(2007/10/03)
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- Lewis acid-activated chiral leaving group: Enantioselective electrophilic addition to prochiral olefins
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A new strategy using a BINOL derivative as a chiral leaving group and Lewis acid has been developed for enantioselective alkylation of prochiral olefins. (R)-2,2′-Bis[2-(trimethylsilyl)ethoxy- methyl]-1,1′-binaphthol is demonstrated to be an effective reagent for enantioselective hydroxymethylation of silyl enol ethers and trisubstituted alkenes. Electrophilic addition to prochiral olefins is accompanied by cleavage of an acetal that is dual activated by SnCl4 and the δ-effect of silicon through the SN2 substitution process. Enantioselective synthesis of cyclic terpenes is also described using this strategy.
- Nakamura, Hiroko,Ishihara, Kazuaki,Yamamoto, Hisashi
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p. 5124 - 5137
(2007/10/03)
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- Asymmetric synthesis of (R)-limonene and (S)-cembrene-A by an intramolecular cyclization reaction using a chiral leaving group
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A six-membered monocyclic terpene, (R)-limonene, and a 14-membered monocyclic diterpene, (S)-cembrene-A, have been synthesized, respectively, by new enantioselective intramolecular cyclization reactions of neryl ether and (all-E)-geranylgeranyl ether using an (R)- 1,1′-binaphthyl-2-benzoxy-2′-oxy auxiliary as a chiral leaving group in the presence of tin(IV) chloride.
- Ishihara,Nakamura,Yamamoto
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p. 1113 - 1116
(2007/10/03)
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- Enantioselective Terpene Syntheses by Diels-Alder Reaction of 1-(1-Arylalkoxy)-2-methyl-1,3-butadiene with Isoprene
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The (R)- and (S)-1-(1-arylalkoxy)-2-methyl-1,3-butadienes 6 undergo cycloadditions with excess isoprene (7) under pressure to yield not only the expected (4S,6R)- and (4R,6S)-trans-carveol (8) with up to 96percent e.e. but also up to 40percent of (R)- and (S)-limonene (9) with up to 93percent e.e.Asymmetric induction is proposed to arise from a transition state involving definite ? stacking of one molecule of isoprenyl ether and two molecules of isoprene.Key Words: (4S,6R)-, (4R,6S)-trans-Carveol / (R)-, (S)-Limonene / Isoprene / Isoprenyl ether / Cycloaddition, diastereo-, enantioselective
- Zadel, Guido,Rieger, Rainer,Breitmaier, Eberhard
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p. 1343 - 1346
(2007/10/02)
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- Reductive Deoxygenation of α,β-Unsatured Ketones via Cyanophosphates by Lithium in Liquid Ammonia
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A new method for deoxygenation of α,β-unsatured ketones via cyanophosphates by lithium metal in liquid ammonia is described
- Yoneda, Ryuji,Osaki, Hirotaka,Harusawa, Shinya,Kurihara, Takushi
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p. 2817 - 2818
(2007/10/02)
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- Biosynthesis of Cyclic Monoterpenoids. Involvement of Stereochemically Specified Linalyl Cation in the Cyclization of C10-Prenyl Chain
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Incubation of geranyl diphosphate (GPP) and the enantiomers and racemate of linalyl diphosphate (LPP) with the limonene synthetase isolated from Mentha spicata resulted in the conversion of GPP and (S)-LPP into (S)-limonene; this can be taken as evidence that linalyl cation having not only the (S)-LPP-like configuration but also C-1 and C-6 bouble bonds situated in the anti spatial arrangement is involved in the process of the cyclization of GPP to (S)-limonene.The intermediacy of the linalyl cation was supported by the evaluation of the potential energy of the cation with the MO calculation.
- Suga, Takayuki,Hirata, Toshifumi,Izumi, Shunsuke,Hiraga, Yoshikazu,Okamoto, Kazuki
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p. 115 - 118
(2007/10/02)
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- CHIRAL LEAVING GROUP: ASYMMETRIC SYNTHESIS OF LIMONENE AND BISABOLENE
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The biogenetic-type asymmetric synthesis of limonene and bisabolenes is described.As model studies for the present asymmetric synthesis, the cyclization of catechol, biphenol and binaphthol mononeryl ethers 1, 4, and 5, with organoaluminium reagents are executed to furnish limonene as a major product.Since the reaction of 1, 4, and 5 has proved to proceed much faster than that of neryl phenyl ether under the similar conditions, the rate acceleration is attributed to the novel metal-anchimeric assistance of the aluminium reagents bound with the neighboring hydroxyl group for effecting the generation of the allyl cathion.This anchimeric effect is utilized for the enantioselective cyclization of (R)-(+)-1,1'-bi-2-naphthol mononeryl ether (8) upon treatment with modified aluminium reagent 9 to produce limonene with high optical purity (77percent ee).In a similar fashion, (R)-(+)-binaphtol (Z,Z)-monofarnesyl ether 16a undergoes the enantioselective cyclization to give β-bisabolene in 76percent ee.
- Sakane, Soichi,Fujiwara, Junya,Maruoka, Keiji,Yamamoto, Hisashi
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p. 2193 - 2202
(2007/10/02)
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