- Enantioselective oxidation of secondary alcohols by the flavoprotein alcohol oxidase from Phanerochaete chrysosporium
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The enantioselective oxidation of secondary alcohols represents a valuable approach for the synthesis of optically pure compounds. Flavoprotein oxidases can catalyse such selective transformations by merely using oxygen as electron acceptor. While many flavoprotein oxidases preferably act on primary alcohols, the FAD-containing alcohol oxidase from Phanerochaete chrysosporium was found to be able to perform kinetic resolutions of several secondary alcohols. By selective oxidation of the (S)-alcohols, the (R)-alcohols were obtained in high enantiopurity. In silico docking studies were carried out in order to substantiate the observed (S)-selectivity. Several hydrophobic and aromatic residues in the substrate binding site create a cavity in which the substrates can comfortably undergo van der Waals and pi-stacking interactions. Consequently, oxidation of the secondary alcohols is restricted to one of the two enantiomers. This study has uncovered the ability of an FAD-containing alcohol oxidase, that is known for oxidizing small primary alcohols, to perform enantioselective oxidations of various secondary alcohols.
- Tjallinks, Gwen,Martin, Caterina,Fraaije, Marco W.
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- Phosphine-Catalyzed Intermolecular Annulations of Fluorinated ortho-Aminophenones with Alkynones – The Switchable [4+2] or [4+2]/[3+2] Cycloaddition
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A phosphine-catalyzed intermolecular annulation reaction of functionalized ortho-aminoacetophenones with alkynones has been disclosed in this paper. A variety of 2-alkynylquinolines and benzo-fused indolizine were selectively afforded in moderate to good yields at different reaction temperatures and with different phosphine catalysts via the in situ generated zwitterionic intermediate derived from alkynone and phosphine. (Figure presented.).
- Zhang, Yanshun,Sun, Yaoliang,Wei, Yin,Shi, Min
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supporting information
p. 2129 - 2135
(2019/03/13)
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- Diastereoselective synthesis of β-amino ketone and acid derivatives by palladium-catalyzed conjugate addition
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The first diastereoselective synthesis of β-amino ketone and β-amino acid derivatives by palladium-catalyzed conjugate addition of arylboronic acids to chiral β-enamino ketones and β-enamino esters is reported. The catalytic system employing (S)-4-(tert-butyl)oxazolidin-2-one as the chiral auxiliary in water under an air atmosphere provides β-amino ketone and β-amino acid derivatives in high yields with excellent diastereoselectivity.
- Zhi, Wubin,Li, Jingya,Zou, Dapeng,Wu, Yangjie,Wu, Yusheng
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supporting information
p. 2736 - 2740
(2018/06/25)
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- Visible-Light-Induced Efficient Selective Oxidation of Nonactivated Alcohols over {001}-Faceted TiO2 with Molecular Oxygen
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In the presence of molecular oxygen, a {001}-faceted nanocrystalline anatase TiO2 catalyst enabled the selective oxidation of nonactivated aliphatic alcohols to the corresponding aldehydes or ketones under visible light. The reaction shows excellent conversion and selectivity towards the formation of the carbonyl products without over-oxidation to the corresponding carboxylic acids. The exceptional reactivity of the catalyst is possibly due to the absorption of visible light originating from a stronger interaction of alcohol with the {001} facet, which facilitates the modification of the band structure of TiO2, thus facilitating the photogenerated hole transfer and subsequent oxidation processes. The experimental results have also been corroborated by first-principles quantum chemical DFT calculations.
- Vadakkekara, Raji,Biswas, Abul Kalam,Sahoo, Tapan,Pal, Provas,Ganguly, Bishwajit,Ghosh, Subhash Chandra,Panda, Asit Baran
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supporting information
p. 3084 - 3089
(2016/11/13)
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- Supported Palladium Oxide Nanoparticles in SBA-15 as a Heterogeneous Catalyst for the Aerobic Oxidation of Alcohols
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Palladium nanoparticles were first synthesized through the thermal decomposition method and subsequently immobilized on ordered mesoporous silica material, SBA-15, to afford PdO/SBA-15 catalyst. The synthesized catalyst was characterized by X-ray diffraction, nitrogen adsorption-desorption measurement, transmission electron microscopy, and inductively coupled plasma atomic emission spectrometry. The catalytic activity was tested for the aerobic oxidation of alcohols. Easy recovery, high yeilds and relatively short reaction times were observed for the mentioned catalyst.
- Atashin, Hassan,Malakooti, Reihaneh
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p. 1039 - 1044
(2016/02/18)
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- Si-free enolate Claisen rearrangements of enamido substrates
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α-Alkyl β-amino esters are available in high diastereoselectivity through a silicon-free Claisen enolate [3,3]-sigmatropic rearrangement of enamide esters. Optimisation studies have probed the crucial role of the initial enolisation and the nature of the enamide N-centre. The demonstration of chirality transfer and the formation of β-proline systems, is also presented.
- Harker, Wesley R. R.,Carswell, Emma L.,Carbery, David R.
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supporting information; experimental part
p. 1406 - 1410
(2012/04/05)
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- Palladacycle-catalyzed reaction of bicyclic alkenes with terminal ynones: Regiospecific synthesis of polysubstituted furans
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A new synthetic strategy to access polysubstituted furans regiospecifically has been developed using simple bicyclic alkenes and terminal ynones as starting materials with palladacycles as unique active catalysts. A rational mechanism has also been proposed. This reaction features mild reaction conditions, easily available starting materials and palladacycle catalysts, a wide substrate scope, and high regiospecificity.
- Ge, Guang-Cun,Mo, Dong-Liang,Ding, Chang-Hua,Dai, Li-Xin,Hou, Xue-Long
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supporting information
p. 5756 - 5759
(2013/01/15)
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- Sn/Li exchange reactions in 1,ω-distannylated conjugated trienes and tetraenes: An enabling step for polyene synthesis
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Successive treatments of (1E,3E,5E)- or (1E,3Z,5E)-1,6-bis(tributylstannyl) hexa-1,3,5-triene with nBuLi and butanal rendered polyenyl alcohols resulting from one Sn/Li exchange reaction and exhibiting complete retention of the configuration of all C=C bonds. Mono- or dimethylated all-E-configured 1,6-distannylated conjugated trienes as well as all-E-1,8-bis(tributylstannyl) octa-1,3,5,7-tetraene and dimethylated congeners thereof reacted similarly. The respective Sn/Li exchange reactions affected the substructure Bu 3Sn-CH=CH with a 93-94:7-6 preference over Bu3Sn-CMe=CH and with a 90:10 preference over Bu3Sn-CH=CMe. all-E-1-Lithio-6- (tributylstannyl)hexa-1,3,5-triene was incorporated into navenone B after Negishi coupling and into (-)-cicutoxin after acylation. NMR spectroscopy of our navenone B specimen revealed that certain resonances were misassigned previously. Molecular tinkertoy: all-E-1,6-(Tributylstannyl)hexa-1,3,5-triene, all-E-1,8-(tributylstannyl)octa-1,3,5,7-tetraene, and related bis(tributylstannylated) polyenes undergomono-Sn/Li exchange reactions. They set the stage for terminus-differentiating functionalizations, which provide inter alianavenone B and (-)-cicutoxin.
- Burghart, Jochen,Brueckner, Reinhard
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experimental part
p. 150 - 165
(2011/03/18)
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- Structure-reactivity relationship for alcohol oxidations via hydride transfer to a carbocationic oxidizing agent
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Second-order rate constants were determined for the oxidation of 27 alcohols (R1R2CHOH) by a carbocationic oxidizing agent, 9-phenylxanthylium ion, in acetontrile at 60°C. Alcohols include open-chain alkyl, cycloalkyl, and unsaturated alcohols. Kinetic isotope effects for the reaction of 1-phenylethanol were determined at three H/D positions of the alcohol (KIEα-D=3.9, KIEβ-D3=1.03, KIE OD=1.10). These KIE results are consistent with those we previously reported for the 2-propanol reaction, suggesting that these reactions follow a hydride-proton sequential transfer mechanism that involves a rate-limiting formation of the α-hydroxy carbocation intermediate. Structure-reactivity relationship for alcohol oxidations was deeply discussed on the basis of the observed structural effects on the formation of the carbocationic transition state (Cδ+-OH). Efficiencies of alcohol oxidations are largely dependent upon the alcohol structures. Steric hindrance effect and ring strain relief effect win over the electronic effect in determining the rates of the oxidations of open-chain alkyl and cycloalkyl alcohols. Unhindered secondary alkyl alcohols would be selectively oxidized in the presence of primary and hindered secondary alkyl alcohols. Strained C7-C11 cycloalkyl alcohols react faster than cyclohexyl alcohol, whereas the strained C5 and C12 alcohols react slower. Aromatic alcohols would be efficiently and selectively oxidized in the presence of aliphatic alcohols of comparable steric requirements. This structure-reactivity relationship for alcohol oxidations via hydride-transfer mechanism is hoped to provide a useful guidance for the selective oxidation of certain alcohol functional groups in organic synthesis. Copyright
- Lu, Yun,Bradshaw, Joshua,Zhao, Yu,Kuester, William,Kabotso, Daniel
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p. 1172 - 1178
(2013/01/12)
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- N-Vinylpyridinium tetrafluoroborate salts as reagents for the stereoselective and regioselective synthesis of symmetrical (2E,4E)-1,6-dioxo-2,4-dienes
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We had previously demonstrated the utility of N-vinylpyridinium tetrafluoroborate salts as novel electrophilic coupling partners in Pd(0)-catalyzed Suzuki cross-coupling reactions with aryl and vinyl boronic acids. We now report that these crystalline, air-stable, and non-hygroscopic salts are also useful reagents for the synthesis of symmetrical (2E,4E)-1,6-dioxo-2,4-dienes (diene diones), which in turn are valuable starting materials for the synthesis of various five-membered heterocycles. The optimization of reaction conditions and the scope and limitations of the reductive dimerization are discussed.
- Gao, Ge,Brown, Neil,Minatoya, Machiko,Buszek, Keith R.
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scheme or table
p. 6491 - 6494
(2009/04/06)
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- The hydroxyl radical reaction rate constant and products of 3,5-dimethyl-1-hexyn-3-ol
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A bimolecular rate constant, κDHO, of (29 ± 9) × 10-12 cm3 molecule-1 s-1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 3,5-dimethyl-1-hexyn-3-ol (DHO, HC≡CC(OH)(CH3)CH2CH(CH3 2) at (297 ± 3) K and 1 atm total pressure. To more clearly define DHO's indoor environment degradation mechanism, the products of the DHO + OH reaction were also investigated. The positively identified DHO/OH reaction products were acetone ((CH3 2C=O), 3-butyne-2-one (3B2O, HC≡CC(=O)(CH3)), 2-methyl-propanal (2MP, H(O=)CCH(CH3)2), 4-methyl-2-pentanone (MIBK, CH3C(=O CH2 CH(CH3)2), ethanedial (GLY, HC(=O C(=O)H), 2-oxopropanal (MGLY, CH3C(=O)C(=O)H), and 2,3-butanedione (23BD, CH3C(=O)C(=O)CH3). The yields of 3B2O and MIBK from the DHO/OH reaction were (8.4 ± 0.3) and (26 ± 2)%, respectively. The use of derivatizing agents O-(2,3,4,5,6-pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O-bis (trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible DHO/OH reaction mechanisms based on previously published volatile organic compound/OH gas-phase reaction mechanisms.
- Wells
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p. 534 - 544
(2007/10/03)
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- Synthesis and biological evaluation of novel 1β-methylcarbapenems with isothiazoloethenyl side chains
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The synthesis of novel 1β-methylcarbapenems 1a,b bearing isothiazoloethenyl moieties at C-5 position of pyrrolidine ring and their biological evaluation are described. Both compounds showed potent and well-balanced antibacterial activity as well as high stability to DHP-I. Especially, 5-isothiazole derivative 1a exhibited excellent DHP-I stability and advanced pharmacokinetics profiles, compared to 5-isoxazole derivative 2, imipenem, and meropenem.
- Kang, Yong Koo,Lee, Kyung Seok,Yoo, Kyung Ho,Shin, Kye Jung,Kim, Dong Chan,Lee, Chang-Seok,Kong, Jae Yang,Kim, Dong Jin
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p. 463 - 466
(2007/10/03)
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- Synthesis and characterization of coordinatively unsaturated alkynyl- and aryl-cobalt complexes with 15 valence electrons, TpiPr2Co-R, bearing the hydrotris(3,5-diisopropylpyrazolyl)borato ligand (TpiPr2)
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Coordinatively unsaturated 15e alkynyl- (TpiPr2Co-C≡C-R) and aryl-cobalt complexes (TpiPr2Co-aryl) bearing the hydrotris(3,5-diisopropylpyrazolyl)borato ligand (TpiPr2) are prepared by dehydrative condensation of the hydroxo complex [TpiPr2Co(μ-OH)2]2 with 1-alkyne and arylation of the chloro complex TpiPr2Co-Cl with Grignard reagents, respectively. Spectroscopic and crystallographic analyses reveal the apparent C3-symmetrical tetrahedral structures with high-spin electronic configuration (S = 3/2), which should result from the property of the TpiPr2 ligand as a tetrahedral enforcer. The TpiPr2Co and hydrocarbyl fragments, are connected dominantly through σ-bonding interaction, and π-interaction including back-donation is not significant as revealed by EHMO calculations. The Co-C bonds are so polarized as to be readily protonated even by moisture to give the corresponding hydrocarbons, but the reactivity toward unsaturated hydrocarbons turns out to be sluggish. TpiPr2Co-C≡C-COOMe is found to catalyze a rare example of specific linear trimerization of methyl propiolate to give (E,E)-MeOOC(H)C=CH-CH=C(COOMe)-C≡C-COOMe.
- Yoshimitsu, Shin-Ichi,Hikichi, Shiro,Akita, Munetaka
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p. 3762 - 3773
(2008/10/08)
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- Racemic and asymmetric Diels-Alder reactions of 1-(2-oxazolidinon-3-yl)-3-siloxy-1,3-butadienes
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Achiral and chiral 1-(2-oxazolidinon-3-yl)-3-siloxy-1,3-butadienes were prepared from readily available starting materials. Although more stable than the parent 1-amino-3-siloxy dienes, the 1-(2-oxazolidinon-3-yl)-3-siloxy-1,3-butadienes are still very reactive in Diels-Alder reactions, somewhat more than 1,3-dialkoxy-1,3-butadienes (e.g., Danishefsky's diene). The cycloadditions of the achiral and chiral dienes with several different dienophiles were examined. The reactions proceeded in good yield, with modest to high endo selectivity. The chiral dienes exhibited excellent facial selectivity in cycloadditions with α-substituted acroleins, maleic anhydride and N-phenylmaleimide. Upon reduction and hydrolysis of the cycloadducts, substituted cyclohexenones were obtained with ee's ranging from 22% to >98%.
- Janey,Iwama,Kozmin,Rawal
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p. 9059 - 9068
(2007/10/03)
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- Asymmetric reduction of ethynyl ketones and ethynylketoesters by secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus
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Secondary alcohol dehydrogenase (SADH) from Thermoanaerobacter ethanolicus, an NADP-dependent, thermostable oxidoreductase, reduces ethynyl ketones and ethynylketoesters enantioselectively to the corresponding propargyl (propargyl = prop-2-ynyl) alcohols. Ethynyl ketones, in general, are reduced with moderate enantioselectivity (with the exception of 4-methylpent-l-yn-3-one, which gives the (S)-alcohol with >98% ee). Although ethynyl ketones bearing a small (up to n-propyl) alkyl substituent are reduced to (S)-alcohols, larger ethynyl ketones give (R)-alcohols. In contrast, ethynylketoesters are converted to (R)-ethynylhydroxyesters of excellent optical purity. Unexpectedly, isopropyl ethynylketoesters give higher chemical yields and higher enantioselectivities of ethynylhydroxyesters than methyl or ethyl ethynylketoesters. The optically pure ethynylhydroxyesters may serve as useful chiral building blocks for asymmetric synthesis.
- Heiss, Christian,Phillips, Robert S.
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p. 2821 - 2825
(2007/10/03)
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- Cis-dioxomolybdenum(VI) complexes as new catalysts for the Meyer-Schuster rearrangement
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We describe a new catalytic system for the isomerisation of propargylic alcohols into α,β-ethylenic carbonyl derivatives (Meyer-Schuster rearrangement), based on the combination of dioxomolybdenum(IV) catalysts and sulfoxides.
- Lorber, Christian Y.,Osborn, John A.
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p. 853 - 856
(2007/10/03)
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- Thermal Rearrangements, XXII. The Propargyl-Cope Rearrangement of meso- and d,l-3,4-Dimethyl-1,5-hexadiyne-3,4-diol
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The thermal behavior of meso- and d,l-3,4-dimethyl-1,5-hexadiyne-3,4-diol (meso- and d,l-4) has been studied at 400 deg C in the gas phase.In a tandem reaction the diols isomerize via the bisallenes 5 first to cis- and trans-3,4-diacetylcyclobutene (cis- and trans-8) which have been detected as intermediates by 13C-NMR spectroscopy as well as catalytic hydrogenation to 1,2-diacetylcyclobutane (9).Subsequently, 8 stabilizes itself by ring opening to (E,Z)- and (E,E)-3,5-octadien-2,7-dione .As a side reaction retro-ene cleavage of 4 to 2-butynone (10) and methyl vinyl ketone (12) is observed.By pyrolysis of the pure diastereomers 4 it is shown that the retro-ene process is more pronounced in the d,l than in the meso series. - Key Words: Rearrangements, thermal / Propargyl-Cope reaction / 1,5-Hexadiyne-3,4-diol / Cyclobutene, 3,4-diacetyl- / Fragmentations, retro-ene / Tandem reactions
- Hopf, Henning,Hamann, Uwe,Zimmermann, Gerhard,Remmler, Matthias
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p. 959 - 964
(2007/10/02)
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- A Pseudomonas sp. Alcohol Dehydrogenase with Broad Substrate Specificity and Unusual Stereospecificity for Organic Synthesis
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A new alcohol dehydrogenase from Pseudomonas sp. strian PED has been isolated and characterized.The enzyme exhibits a broad substrate specificity, accepting aromatic, cyclic, and aliphatic compounds as substrates.The Km values were determined as 525 μM for NAD and 75 μM for 2-propanol with a specific activity of 36 U/mg.The kinetic mechanism is ordered bi-bi with the cofactor binding first and releasing last.The enzyme transfers the pro-R hydride of NADH to the si face of carbonyl compounds to yield (R) alcohols.Synthetic-scale reductions of a number of representative compounds were carried out in high enentiomeric excess with in situ regeneration of NADH using 2-propanol as the hydride source and the same enzyme as catalyst.
- Bradshaw, Curt W.,Fu, Hong,Shen, Gwo-Jenn,Wong, Chi-Huey
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p. 1526 - 1532
(2007/10/02)
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- VALENCE ISOMER INTERCONVERSION OF NORBORNADIENES AND QUADRICYCLANES HAVING AN ACYL GROUP
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As a model for light energy conversion, various acylnorbornadienes and their corresponding valence isomers acylquadricyclanes have been prepared.Among these (19) and (31) were found to be the best pair for the purpose because of the visible light absorption of (19), a high quantum yield for its photocycloaddition and a rapid and complete reversion of (31) to (19) with an acid catalyst.
- Hirao, Ken-ichi,Yamashita, Asami,Ando, Akira,Hamada, Tatsuo,Yonemitsu, Osamu
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p. 2913 - 2916
(2007/10/02)
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- The Cycloaddition of 1,6-Dihydro-2-dimethylamino-4,6,6-trimethylpyrimidine with Acetylenic Compounds
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1,6-Dihydro-2-dimethylamino-4,6,6-trimethylpyrimidine reacted with acetylenic compounds containing electron-withdrawing groups to yield 2-dimethylaminopyridine derivatives.When monosubstituted acetylenes were used, 4-unsubstituted pyridines were selectively obtained.The results of MINDO/3 calculations are consistent with this regioselectivity.Keywords--1,6-dihydropyrimidine; cycloaddition; acetylenic compound; pyridine derivative; MINDO/3 calculation
- Kashima, Choji,Shimizu, Masao,Omote, Yoshimori
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p. 2694 - 2697
(2007/10/02)
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- Phenyl Cations as Reactive Intermediates in the Solvolysis of Dien-in-yl Triflates
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The synthesis, separation, and solvolysis of the stereoisomeric 1,4-dimethyl-1,3-hexadien-5-yn-1-yl triflates 15a - c in various solvents are described.In contrast to the (Z)-isomers 15a - c, the (E)-isomers 15a - c react preferably via an intermediate phenyl cation 16 to give the phenyl ethers 17.Further mechanistic investigations which support the formation of the intermediate phenyl cations 16 are described.The formation of the benzylic derivatives 18 is discussed.
- Holweger, Walter,Hanack, Michael
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p. 3004 - 3020
(2007/10/02)
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