- Imine exchange in O-aryl and O-alkyl oximes as a base reaction for aqueous 'dynamic' combinatorial libraries. A kinetic and thermodynamic study
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Kinetics and mechanisms of the imine exchange reactions of O-alkyl and O-aryl oximes with O-alkyl-and O-aryloxyamines, respectively, were studied by 1H NMR spectroscopy in aqueous solutions. The reaction between benzaldehyde O-methyloxime and O-ethylhydroxylamine at 60 °C is first order in both oxime and the alkoxylamine (the second-order rate constant k2 = 0.86 ± 0.081 mol-1 min-1 at pD 2.9). the reaction being subject to acidic catalysis. A similar imine transfer was studied in the reaction of 1,3-diaminooxyprog with bifunctional oximes. Testing of various additives as potential catalysts for the reaction revealed imidazole as a moderately effective catalyst. The exchange in O-aryl oximes was studied in the interaction between 3-pyridinealdehyde O-pnenyloxime and O-(p-nitrophenyl)hydroxylamine. The reaction is first order in the oxime, but its is independent on the aryloxyamine concentration and pD. The proposed mechanism involves a rate-limiting hydration of the oxime molecule. Mechanisms of the exchange reactions are discussed in relation to their possible use to generate diverse pools of compounds for the recently proposed 'dynamic' combinatorial chemistry approach Copyright
- Polyakov, Vladimir A.,Nelen, Marina I.,Nazarpack-Kandlousy, Noureddin,Ryabov, Alexander D.,Eliseev, Alexey V.
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Read Online
- One-pot synthesis of oxime ethers from benzaldehyde or acetophenone, hydroxylamine salt, potassium hydroxide, and alkyl halides
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Oxime ethers were synthesized in one-pot reaction from benzaldehyde or acetophenone, hydroxylamine hydrogen chloride, alkyl halides and KOH in aqueous DMSO. The reactions were completed in 15-50 min with yields in 80-96%.
- Li, Chunbao,Zhang, Hang,Cui, Yi,Zhang, Shuanming,Zhao, Zheyuan,Choi, Michael C. K.,Chan, Albert S. C.
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Read Online
- Change of Orientation in Electrophilic Substitution of Benzaldehydes by O-Alkyloximation Derivatives
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By the introduction of O-alkyloxyimino group, orientation in electrophilic substitution of benzaldehyde can be selectively controlled.
- Goda, Hiroshi,Ihara, Hirotaka,Hirayama, Chuichi,Sato, Makoto
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Read Online
- A Short Total Synthesis of Benzophenanthridine Alkaloids via a Rhodium(III)-Catalyzed C-H Ring-Opening Reaction
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The biologically important naturally available benzophenanthridines were prepared efficiently in three steps with overall good yields. A new synthetic methodology involving a rhodium(III) catalyzed redox-neutral ring-opening of 7-azabenzonorbornadienes with aromatic aldoximes is developed to synthesize the target molecules. The developed C-H ring-opening reaction is highly diastereoselective and compatible with various sensitive functional group substituted aromatic aldoximes as well as substituted 7-azabenzonorbornadienes. The ring-opening products were transformed into highly sensitive 13,14-dehydrobenzo phenanthridine derivatives by HCl hydrolysis. Subsequently, 13,14-dehydrobenzophenanthridines were converted into biologically important benzophenanthridine alkaloids in the presence of DDQ. A possible reaction mechanism was proposed for the C-H ring-opening reaction and supported by the deuterium labeling studies.
- Aravindan, Narasingan,Jeganmohan, Masilamani
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p. 14826 - 14843
(2021/10/20)
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- Compound and application thereof
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The compound has the structure shown in the formula (I) or the formula (II) and R. 1 Selected from H. Deuterium, halogen, cyano, nitro, alkenyl, alkynyl, carboxy, C1 - C20 chain alkyl, C3 - C20 cycloalkyl, C1 - C20 alkoxy, substituted or unsubstituted C6 - C60 aryl, substituted or unsubstituted C3 - C60 heteroaryl, and the heteroatom in the heteroaryl is selected from O or S. L Is one selected from a single bond, a substituted or unsubstituted C6 - C60 arylene group, a substituted or unsubstituted C3 - C60 heteroarylene group. R Is one selected from H, deuterium, halogen, cyano, nitro, alkenyl, alkynyl, carboxy, C1 - C20 chain alkyl, C3 - C20 cycloalkyl, C1 - C20 alkoxy, substituted or unsubstituted C6 - C60 aryl, substituted or unsubstituted C3 - C60 heteroaryl. Ar Is a substituted or unsubstituted C6 - C60 aryl group, a substituted or unsubstituted C3 - C60 heteroaryl group. When the compound is applied OLED devices, the device efficiency can be effectively improved, the driving voltage is reduced, and the compound is a good-performance electronic transmission material.
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Paragraph 0151; 0153-0155
(2021/10/05)
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- Nickel versus Palladium in Cross-Coupling Catalysis: On the Role of Substrate Coordination to Zerovalent Metal Complexes
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A detailed comparison of the effect of coordinating functional groups on the performance of Suzuki-Miyaura reactions catalysed by nickel and palladium is reported, using competition experiments, robustness screening, and density functional theory calculations. Nickel can interact with a variety of functional groups, which manifests as selectivity in competitive cross-coupling reactions. The presence of these functional groups on exogenous additives has effects on cross-coupling reactions that range from a slight improvement in yield to the complete cessation of the reaction. In contrast, palladium does not interact sufficiently strongly with these functional groups to induce selectivity in cross-coupling reactions; the selectivity of palladium-catalysed cross-coupling reactions is predominantly governed by aryl halide electronic properties.
- Burton, Paul M.,Cooper, Alasdair K.,Nelson, David J.
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p. 565 - 573
(2020/02/13)
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- Nickel-Catalyzed Transformation of Alkene-Tethered Oxime Ethers to Nitriles by a Traceless Directing Group Strategy
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Nickel-catalyzed transformation of alkene-tethered oxime ethers to nitriles using a traceless directing group strategy has been developed. A series of alkene-tethered oxime ethers derived from benzaldehyde and cinnamyl aldehyde derivatives were converted into the corresponding benzonitriles and cinnamonitriles in 46-98% yields using the nickel catalyst system. Control experiments showed that the alkene group tethered to an oxygen atom on the oximes via one methylene unit plays a key role as a traceless directing group during the catalysis.
- Takahashi, Yoshiyuki,Tsuji, Hiroaki,Kawatsura, Motoi
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p. 2654 - 2665
(2020/02/04)
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- Nitrate promoted mild and versatile Pd-catalysed C(sp2)-H oxidation with carboxylic acids
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A nitrate-promoted Pd-catalysed mild cross-dehydrogenative C(sp2)-H bond oxidation of oximes or azobenzenes with diverse carboxylic acids has been developed. In contrast to the previous catalytic systems, this protocol features mild conditions (close to room temperature for most cases) and a broad substrate scope (up to 64 examples), thus constituting a versatile method to directly prepare diverse O-aryl esters. Moreover, the superiority of the nitrate additive in this mild transformation was further determined by experimental and computational evidence.
- Hao, Hong-Yan,He, Yu-Ting,Lou, Shao-Jie,Luo, Gen,Mao, Yang-Jie,Xiong, Xue,Xu, Dan-Qian,Xu, Zhen-Yuan
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supporting information
p. 6732 - 6737
(2020/09/21)
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- Palladium-catalyzed C-H activation/C-C cross-coupling reactions: Via electrochemistry
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Palladium-catalyzed C-H activation/C-C cross-coupling reactions typically require stoichiometric chemical oxidants and exogenous ligands. However, there are significant disadvantages associated with the use of traditional stoichiometric oxidants. To overcome these issues, we have developed an electrochemical strategy to achieve methylation and acylation.
- Ma, Cong,Zhao, Chuan-Qi,Li, Yi-Qian,Zhang, Li-Pu,Xu, Xue-Tao,Zhang, Kun,Mei, Tian-Sheng
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supporting information
p. 12189 - 12192
(2017/11/16)
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- Palladium-catalyzed enolate arylation as a key C-C bond-forming reaction for the synthesis of isoquinolines
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The palladium-catalyzed coupling of an enolate with an ortho-functionalized aryl halide (an α-arylation) furnishes a protected 1,5-dicarbonyl moiety that can be cyclized to an isoquinoline with a source of ammonia. This fully regioselective synthetic route tolerates a wide range of substituents, including those that give rise to the traditionally difficult to access electron-deficient isoquinoline skeletons. These two synthetic operations can be combined to give a three-component, one-pot isoquinoline synthesis. Alternatively, cyclization of the intermediates with hydroxylamine hydrochloride engenders direct access to isoquinoline N-oxides; and cyclization with methylamine, gives isoquinolinium salts. Significant diversity is available in the substituents at the C4 position in four-component, one-pot couplings, by either trapping the in situ intermediate after α-arylation with carbon or heteroatom-based electrophiles, or by performing an α,α-heterodiarylation to install aryl groups at this position. The α-arylation of nitrile and ester enolates gives access to 3-amino and 3-hydroxyisoquinolines and the α-arylation of tert-butyl cyanoacetate followed by electrophile trapping, decarboxylation and cyclization, C4-functionalized 3-aminoisoquinolines. An oxime directing group can be used to direct a C-H functionalization/bromination, which allows monofunctionalized rather than difunctionalized aryl precursors to be brought through this synthetic route.
- Pilgrim, Ben S.,Gatland, Alice E.,Esteves, Carlos H. A.,McTernan, Charlie T.,Jones, Geraint R.,Tatton, Matthew R.,Procopiou, Panayiotis A.,Donohoe, Timothy J.
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p. 1065 - 1090
(2016/01/15)
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- Synthesis of 2-fluorocholine aryl carbonyl compounds
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The invention provides a method for synthesizing 2-fluoroarylcarbonyl compounds, which comprises the following steps: converting arylcarbonyl compounds into corresponding carbonyl oxime ether compounds, mildly implementing aryl hydrocarbon chain direct fluoridation of high-selectivity oximido substituent group ortho-position in the presence of a palladium catalyst, a fluoridation reagent and additives, and finally, rehydrolyzing oxime ethers under the action of acid to obtain the 2-fluoroarylcarbonyl compounds. The fluoridation method has the advantages of mild reaction conditions, high substrate adaptability, high fluoridation selectivity and the like, is simple to operate, and has higher application research value.
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Paragraph 0100
(2017/02/09)
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- A O-nitrobenzaldehyde synthetic method of compound
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The invention provides a preparation method for an o-nitrobenzaldehyde compound. The method directly taking benzaldehyde compounds as starting raw materials comprises the following steps: firstly, converting a formyl group into an O-methyl oximido; secondly, taking divalent palladium salt as a catalyst, and realizing the carbon-hydrogen bond activation single nitration reaction on an o-position of an oximido under the condition that both an oxidant and a nitration agent exist; finally, removing the O-methyl oximido by using strong organic acid to obtain the o-nitrobenzaldehyde compound. The nitration method provided by the invention has the advantage of specificity in the o-position of a nitration position, the reaction process is safe and environment-friendly, the substrate is excellent in adaptability, and various substituents can realize o-position nitration; various benzaldehyde is directly taken as raw materials, so that the reaction steps are simple, and the synthesizing method is a novel route for synthesizing various o-nitrobenzaldehyde compounds containing substituents.
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Paragraph 0047
(2016/10/07)
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- An effective Biginelli-type synthesis of 1-methoxy-3,4-dihydropyrimidin-2(1H)-ones
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Abstract The ternary condensation of N-methoxyurea, aldehydes, and 1,3-dicarbonyl compounds, resulting in novel 1-methoxy-3,4-dihydropyrimidin-2(1H)-ones has been examined. Commonly used reaction conditions and catalysts (EtOH/HCl, HOAc, DMF) proved to be
- Kolosov, Maksim A.,Kulyk, Olesia G.,Al-Ogaili, Muataz J.K.,Orlov, Valeriy D.
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supporting information
p. 4666 - 4669
(2015/08/06)
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- Regiospecific synthesis of substituted 2-nitrobenzaldehydes from benzaldehydes through palladium-catalyzed chelation-assisted C-H nitration
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A regiospecific synthesis of substituted 2-nitrobenzaldehydes from substituted benzaldehydes has been developed that involves a three-step process with palladium-catalyzed chelation-assisted C-H nitration as the key step. In the process, O-methyl aldoxime serves as a removable directing group for the palladium-catalyzed ortho-nitration of substituted benzaldoximes and it can be removed in subsequent conversion of the resulting 2-nitrobenzaldoximes into 2-nitrobenzaldehydes.
- Zhang, Wei,Wu, Degui,Zhang, Jian,Liu, Yunkui
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p. 5827 - 5835
(2014/10/15)
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- Palladium-catalyzed decarboxylative acylation of O-methyl ketoximes with α-keto acids
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A mild, practical and efficient palladium-catalyzed decarboxylative ortho-acylation of O-methyl ketoximes with α-keto acids via C-H bond activation is described. In these reactions, a broad range of O-methyl ketoximes and α-keto acids undergoes the decarboxylative cross-coupling reactions with high selectivities and good tolerance. The Royal Society of Chemistry 2013.
- Kim, Minyoung,Park, Jihye,Sharma, Satyasheel,Kim, Aejin,Park, Eonjeong,Kwak, Jong Hwan,Jung, Young Hoon,Kim, In Su
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supporting information
p. 925 - 927
(2013/02/23)
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- Rhodium-catalyzed directed C-H cyanation of arenes with N-cyano-N-phenyl-p-toluenesulfonamide
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A Rh-catalyzed directed C-H cyanation reaction was developed for the first time as a practical method for the synthesis of aromatic nitriles. N-Cyano-N-phenyl-p-toluenesulfonamide, a user-friendly cyanation reagent, was used in the transformation. Many different directing groups can be used in this C-H cyanation process, and the reaction tolerates a variety of synthetically important functional groups.
- Gong, Tian-Jun,Xiao, Bin,Cheng, Wan-Min,Su, Wei,Xu, Jun,Liu, Zhao-Jing,Liu, Lei,Fu, Yao
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supporting information
p. 10630 - 10633
(2013/08/23)
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- Palladium-catalyzed direct acylation of ketoximes and aldoximes from the alcohol oxidation level through C-H bond activation
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A highly efficient palladium-catalyzed oxidative ortho-acylation of O-methyl ketoximes and O-methyl aldoximes with benzylic and aliphatic alcohols from the alcohol oxidation level is described. This protocol potentially provides new opportunities to use readily available alcohols as starting materials for catalytic reactions, and represents a catalytic alternative to transcend the barriers imposed by classical Friedel-Crafts acylation. A highly efficient palladium-catalyzed oxidative ortho-acylation of O-methyl ketoximes and O-methyl aldoximes with benzylic and aliphatic alcohols from the alcohol oxidation level is described. Copyright
- Sharma, Satyasheel,Kim, Minyoung,Park, Jihye,Kim, Mirim,Kwak, Jong Hwan,Jung, Young Hoon,Oh, Joa Sub,Lee, Youngil,Kim, In Su
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p. 6656 - 6665
(2013/11/06)
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- Metal-Free 2,2,6,6-tetramethylpiperidin-1-yloxy radical (TEMPO) catalyzed aerobic oxidation of hydroxylamines and alkoxyamines to oximes and oxime ethers
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TEMPO-Mediated oxidation of hydroxylamines (=hydroxyamines) and alkoxyamines to the corresponding oxime derivatives is reported (TEMPO=2,2,6,6-tetramethylpiperidin-1-yloxy radical; Scheme 2). These environmentally benign oxidations proceed in good to excellent yields (Table 1). For alkoxyamines, oxidation to the corresponding oxime ethers can be performed by using dioxygen as a terminal oxidant in the presence of 5-10 mol-% of TEMPO or 4-substituted derivatives thereof as a catalyst (Scheme 3 and Table 2). Importantly, benzyl bromides can directly be transformed to oxime ethers via in situ alkoxyamine formation by a nucleophilic substitution followed by TEMPO-mediated oxidation (Scheme 4 and Table 3). Copyright
- Wertz, Sebastian,Studer, Armido
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p. 1758 - 1772,15
(2012/12/13)
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- Selective ortho -bromination of substituted benzaldoximes using Pd-catalyzed C-H activation: Application to the synthesis of substituted 2-bromobenzaldehydes
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Substituted 2-bromobenzaldehydes were synthesized from benzaldehydes using a three-step sequence involving a selective palladium-catalyzed ortho-bromination as the key step. O-Methyloxime serves as a directing group in this reaction. A rapid deprotection of substituted 2-bromobenzaldoximes afforded substituted 2-bromobenzaldehydes with good overall yields.
- Dubost, Emmanuelle,Fossey, Christine,Cailly, Thomas,Rault, Sylvain,Fabis, Frederic
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experimental part
p. 6414 - 6420
(2011/09/16)
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- (1-Alkynyl)dicarbonylcyclopentadienyliron complexes as electron-rich alkynes in organic synthesis: BF3-mediated [2+2] cycloaddition/ring- opening providing (2-alkenyl-1-imino)iron complexes
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Strike while the iron is hot! A BF3-mediated formal [2+2] cycloaddition between (1-alkynyl)iron complexes and aromatic aldehyde imines occurs, which is followed by ring-opening of the initially formed azacyclobutenes to yield (2-alkenyl-1-imino)iron complexes (see scheme). The resulting iron complexes undergo deferric substitution reactions with water under oxidative conditions to afford the corresponding cinnamamides with high E selectivity.
- Nakaya, Ryotaro,Yasuda, Shigeo,Yorimitsu, Hideki,Oshima, Koichiro
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supporting information; experimental part
p. 8559 - 8561
(2011/09/20)
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- Highly efficient formation of nitriles and alkoxy radicals from N-alkoxybenziminoyl chlorides in solution
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A series of N-alkoxybenziminoyl chlorides were synthesized and reacted with tributyltin hydride in the presence of AIBN to generate the corresponding N-alkoxybenziminoyl radicals. This methodology successfully generates the desired radicals, which undergo a rapid and highly efficient β-scission reaction, as shown by the formation of the corresponding nitriles and products derived from alkoxy radicals. The intermediate N -alkoxybenziminoyl radical could not be trapped by employing high concentrations of Bu3SnH or by using a hydrogen atom donating solvent such as toluene. The fast β-scission reaction was found to be independent of the structure of the iminoyl chloride. These results are different from studies on the similar N-alkyliminoyl radicals, which typically give products from both β-scission hydrogen atom transfer pathways. Using the data from this study as well as some reported rate constants for different hydrogen atom transfer (HAT) processes, we conclude that the lower limit for the rate constant for the β-scission process (kβ)in N-alkoxybenziminoyl radicals is 2.5 × 107 s-1.
- De Peter Lijser,Burke, Cassandra R.,Rosenberg, Jonathan,Hunter, Jordan
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supporting information; experimental part
p. 1679 - 1684
(2009/10/01)
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- One-pot synthesis of alkoxyamine derivatives by reductive alkoxyamination with a 2-picoline-borane complex
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Reduction of oxime ethers with a 2-picoline-borane complex was examined to give alkoxyamine derivatives. The reduction was found to proceed in the presence of aqueous HCl in MeOH-AcOH. The method was extended to one-pot synthesis of alkoxyamine derivative
- Kawase, Yasushi,Yamagishi, Takehiro,Kutsuma, Teruo,Ueda, Kimio,Iwakuma, Takeo,Nakata, Tadashi,Yokomatsu, Tsutomu
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body text
p. 463 - 470
(2009/06/08)
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- Stereoselective synthesis of quaternary center bearing azetines and their β-amino acid derivatives
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(Chemical Equation Presented) We describe here the use of a stable, four-membered azetine heterocycle for the preparation of highly substituted β-amino acid derivatives. Imidazolidinone chiral auxiliaries were found to eliminate a competitive reaction pathway that had been present under previously reported conditions for azetine synthesis. The ephedrine derived imidazolidin-2-one 21 was allowed to react as its chlorotitanium enolate with O-methyl or -benzyl oximes under optimized conditions to gain improved access to azetines at the gram scale. The azetines were further found to undergo alkylation with complete diastereocontrol, affording the creation of a quaternary center. Subsequent ring opening with benzoyl chloride and auxiliary cleavage provided the corresponding β2,2,3-amino carbonyl derivatives in good yields.
- MacNevin, Christopher J.,Moore, Rhonda L.,Liotta, Dennis C.
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p. 1264 - 1269
(2008/04/05)
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- Probing the aglycon promiscuity of an engineered glycosyltransferase
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(Figure Presented) A sweet library: Two variants (wild-type (WT) and a triple mutant) of glycosyltransferase (GT) OleD have been shown to catalyze glycosylation of over 70 substrates, formation of O-, S- and N-glycosidic bonds, and iterative glycosylation (see scheme). Identified substrates include nucleophiles not previously known to act in GT reactions and span numerous natural product and therapeutic drug classes.
- Gantt, Richard W.,Goff, Randal D.,Williams, Gavin J.,Thorson, Jon S.
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supporting information; experimental part
p. 8889 - 8892
(2009/05/26)
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- Mechanistic aspects of the formation of aldehydes and nitriles in photosensitized reactions of aldoxime ethers
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(Chemical Equation Presented) The photooxidation of a series of aldoxime ethers was studied by laser flash photolysis and steady-state (product studies) methods. Nanosecond laser flash photolysis studies have shown that chloranu (CA)-sensitized reactions of the O-methyl (1), O-ethyl (2), O-benzyl (3), and O-tert-butyl (4) benzaldehyde oximes result in the formation of the corresponding radical cations. In polar non-nucleophilic solvents such as acetonitrile, there are several follow-up pathways available depending on the structure of the aldoxime ether and the energetics of the reaction pathway. When the free energy of electron transfer (ΔGET) becomes endothermic, syn-anti isomerization is the dominant pathway. This isomerization pathway is a result of triplet energy transfer from CA to the aldoxime ether. For substrates with α-protons (aldoxime ethers 1-3), the follow-up reactions involve deprotonation at the α-position followed by β-scission to form the benziminyl radical (and an aldehyde). The benziminyl radical reacts to give benzaldehyde, the major product under these conditions. A small amount of benzonitrile is also observed. In the absence of α-hydrogens (aldoxime ether 4), the major product is benzonitrile, which is thought to occur via reaction of the excited (triplet) sensitizer with the aldoxime ether. Abstraction of the iminyl hydrogen yields an imidoyl radical, which undergoes a β-scission to yield benzonitrile. An alternative pathway involving electron transfer followed by removal of the iminyl proton was not deemed viable based on charge densities obtained from DFT (B3LYP/6-31G*) calculations. Similarly, a rearrangement pathway involving an intramolecular hydrogen atom transfer process was ruled out through experiments with a deuterium-labeled benzaldehyde oxime ether. Studies involving nucleophilic solvents have shown that all aldoxime ethers reacted with MeOH by clean second-order kinetics with rate constants of 0.7 to 1.2 × 107 M-1 s-1, which suggests that there is only a small steric effect in these reactions. The steady-state experiments demonstrated that under these conditions no nitrile is formed. This is explained by a mechanistic scheme involving nucleophilic attack on the nitrogen of the aldoxime ether radical cation, followed by solvent-assisted [1,3]-proton transfer and elimination of an alcohol, similar to the results obtained for a series of acetophenone oxime ethers.
- Peter De Lijser,Rangel, Natalie Ann,Tetalman, Michelle A.,Tsai, Chao-Kuan
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p. 4126 - 4134
(2008/02/04)
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- Ruthenium-catalysed conversion of oxime ethers into nitriles
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The conversion of oxime ethers into nitriles has been achieved under neutral conditions using Ru(CO)(PPh3)3H2 and the bidentate ligand Xantphos as the catalyst.
- Anand, Naveen,Owston, Nathan A.,Parker, Alexandra J.,Slatford, Paul A.,Williams, Jonathan M.J.
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p. 7761 - 7763
(2008/02/12)
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- Palladium-catalyzed aerobic oxidation of amines
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Pd-Catalyzed aerobic oxidation of different amines was systematically examined for the first time. A PdCl2/PPh3 system was successfully developed to catalyze the aerobic oxidation of several types of amines including Ar-CH2NHPh, Ar-CH2NHOMe, and Ar-CH2NHMs with high yields. Theoretical studies showed a remarkable difference in the energy barriers of β-hydride elimination between an alcohol and various amines.
- Wang, Jia-Rui,Fu, Yao,Zhang, Bei-Bei,Cui, Xin,Liu, Lei,Guo, Qing-Xiang
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p. 8293 - 8297
(2007/10/03)
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- Tandem oxidation processes: The direct conversion of activated alcohols into oximes; synthesis of citaldoxime
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The direct conversion of primary alcohols into oximes is reported using manganese dioxide and alkoxylamines/hydroxylamine as their hydrochloride salts or supported on Amberlyst 15. This transformation has been applied to a range of benzylic, allylic and propargylic alcohols and utilised to prepare the natural product citaldoxime.
- Kanno, Hisashi,Taylor, Richard J. K.
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p. 1287 - 1290
(2007/10/03)
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- N-nitroso-N,O-dialkylhydroxylamines: Preparation, structure, and mechanism of the hydronium ion catalysed solvolytic nitrous oxide extrusion reaction
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Eleven N-nitroso-N,O-dialkylhydroxylamines, RN(NO)OR′, have been prepared and the mechanisms of their hydronium ion catalysed solvolyses in aqueous solution which liberate nitrous oxide have been investigated. All reactions are first-order in substrate and first-order in hydronium ion, and the second-order rate constants at 25°C vary over a range of less than 140 in spite of considerable variation in substrate structure (R ranges from methyl to 4-methoxybenzyl to 2-adamantyl, for example) and changes in solvent composition (water with up to 50% methanol or 66% acetonitrile). Enthalpies and entropies of activation are qualitatively similar throughout the range (ΔH?= 72-93 kJ mol-1 and ΔS? = -19 to -57 J K-1 mol-1) which, with the product analyses, are accommodated by a mechanism involving pre-equilibrium protonation of the substrates followed by rate-limiting dissociation to give RN2O+ and HOR′. The oxodiazonium ion intermediate, RN2O+, then dissociates further to give the carbenium ion intermediate, R+, or suffers direct nucleophilic displacement of N2O by solvent (the external nucleophile) or by R′OH (the internal nucleophile liberated in the initial fragmentation). The carbenium ion, R+ (if formed), suffers nucleophilic capture either by solvent or by R′OH. When acetonitrile is the co-solvent (rather than methanol) for the N-(2-adamantyl) substrate 3g, the product of the Ritter reaction, 2-acetamidoadamantane, is detected. These nitrous oxide liberating reactions are compared with the nitric oxide liberating reactions of related N-nitrosohydroxylamines, and the origin of the difference between them is identified. The N(1)-nitroso group in the N,O-dibenzyl compound 3c is shown by X-ray crystallography to be essentially coplanar with the C and O atoms also bonded to N(1).
- Bhat, J. Ishwara,Clegg, William,Maskill, Howard,Elsegood, Mark R.J.,Menneer, Iain D.,Miatt, Peter C.
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p. 1435 - 1446
(2007/10/03)
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- Reductive cleavage of N-O bonds in hydroxylamines and hydroxamic acid derivatives using samarium diiodide
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An efficient process for the reductive cleavage of N-O bonds using samarium diiodide is detailed for a variety of structural types to define the scope and limitations of the method. The reduction is shown to be compatible with base sensitive substrates such as trifluoroacetamide derivatives, which cannot be reduced satisfactorily using aluminum amalgam or sodium amalgam. Direct quenching of the reduction mixture with acylating agents is demonstrated to provide high yields of protected amines in a one-pot process from the N-O derivatives.
- Keck, Gary E.,Wager, Travis T.,McHardy, Stanton F.
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p. 11755 - 11772
(2007/10/03)
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- Stereoselective Synthesis of trans-2-Aryl-3-(2-pyridyl)aziridines from an α-Silyl Carbanion
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Five para-substituted benzaldehyde oxime O-methyl ethers (3) reacted with 2-(trimethylsilylmethyl)pyridine (1) in the presence of lithium di-isopropylamide (LDA) in tetrahydrofuran to give the corresponding trans-2-aryl-3-(2-pyridyl)aziridines (4) in high yield (80, 85, 60, 58, and 74percent, respectively), with small amounts of (Z)-1-amino-1-aryl-2-(2-pyridyl)ethenes (5), and N',N'-di-isopropylbenzamidines (7) as byproducts.The yields of compounds (4) and (5) and their ratio were considerably influenced by experimental conditions (especially molar ratio and the addition method of the reactants).When treated with LDA, compounds (3) were quantitatively converted into benzonitriles, which reacted with anion (2) to give enamines (5) after elimination of a trimethylsilyl group from the corresponding N-trimethylsilyl derivatives, or with additional LDA to give the benzamidine (7); aziridines (4) were not transformed into enamines (5) by the action of LDA.On the basis of these results, a reaction mechanism has been discussed for the formation of compounds (4).
- Konakahara, Takeo,Matsuki, Masayuki,Sugimoto, Shinji,Sato, Kenji
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p. 1489 - 1494
(2007/10/02)
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- Reactions of Oxime Dianions with Electrophiles: An Attempt to Use Aldoximes as Acyl Anion Equivalents and the Synthesis of 2,5-Disubstituted Furans
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The oxime of benzaldehyde (3), when treated with n-butyl-lithium, gave a mixture of the vinyl-lithium (5) and benzonitrile (4).Despite its potential as an acyl anion equivalent, the dianion (5) could only be formed in moderate yield and was always accompanied by elimination products.Aliphatic aldoximes (1) gave the alkyl anion with n-butyl-lithium, but were only alkylated in the case of the Z-isomer.The oxime of furfuraldehyde (8) underwent deprotonation at the 5-position of the furan ring with n-butyllithium - N,N,N',N' - tetramethylethylenediamine in tetrahydrofuran.The resultant dianion (10) was reacted with a variety of electrophiles to give the 2,5-disubstituted furan (9).
- Ager, David J.
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p. 2748 - 2759
(2007/10/02)
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