- Highly chemoselective direct crossed aliphatic-aromatic acyloin condensations with triazolium-derived carbene catalysts
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It has been shown for the first time that triazolium precatalysts promote (in the presence of base) highly chemoselective crossed acyloin condensation reactions between aliphatic and ortho-substituted aromatic aldehydes. An o-bromine atom can serve as a temporary directing group to ensure high chemoselectivity (regardless of the nature of the other substituents on the aromatic ring) which then can be conveniently removed. The process is of broad scope and is operationally simple as it does not require the preactivation of any of the coupling partners to ensure selectivtiy. Preliminary data indicate that highly enantioselective variants of the reaction are feasible using chiral precatalysts.
- O'Toole, Sarah E.,Rose, Christopher A.,Gundala, Sivaji,Zeitler, Kirsten,Connon, Stephen J.
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supporting information; experimental part
p. 347 - 357
(2011/04/17)
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- BIOFUEL PRODUCTION
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Methods, enzymes, recombinant microorganism, and microbial systems are provided for converting polysaccharides, such as those derived from biomass, into suitable monosaccharides or oligosaccharides, as well as for converting suitable monosaccharides or oligosaccharides into commodity chemicals, such as biofuels. Commodity chemicals produced by the methods described herein are also provided. Commodity chemical enriched, refinery-produced petroleum products are also provided, as well as methods for producing the same.
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- Efficient method for the deprotection of tert-butyldimethylsilyl ethers with TiCl4-Lewis base complexes: Application to the synthesis of 1β-methylcarbapenems
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TiCl4-Lewis base (AcOEt, CH3NO2) complexes smoothly deprotected tert-butyldimethylsilyl (TBDMS) ethers. The reaction velocity with these complexes, which seemed less reactive due to the influence of Lewis bases, was considerably greater than that with TiCl4 alone. Selective desilylations between aliphatic and aromatic TBDMS ethers (1 and 5), between 1 and benzyl, allyl, tosyl, methoxyphenyl, and chloroacetyl ethers (13, 14, 15, 16, and 17), and between TBDMS and TBDPS ethers (18 and 19) were successfully performed. Desilylation of TBDMS-aldol, acyloin, and β-lactam analogues 9-12 proceeded smoothly due to anchimeric assistance by the neighboring carbonyl groups. The present method was successfully applied to the practical synthesis of 1β-methylcarbapenems 20a′-f′.
- Iida, Akira,Okazaki, Hiroki,Misaki, Tomonori,Sunagawa, Makoto,Sasaki, Akira,Tanabe, Yoo
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p. 5380 - 5383
(2007/10/03)
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- Stetter reaction in room temperature ionic liquids and application to the synthesis of haloperidol
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Imidazolium-type room temperature ionic liquids (RTILs) have been used for the Stetter reaction, affording the desired 1,4-dicarbonyl compounds in good yields. Thiazolium salts and Et3N are efficient catalysts for this reaction performed in ionic liquid. The possibility to recycle and reuse the solvent has been demonstrated, although it was not possible to recycle the thiazolium catalyst. This method was used in the total synthesis of haloperidol.
- Anjaiah, Siddam,Chandrasekhar, Srivari,Gree, Rene
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p. 1329 - 1334
(2007/10/03)
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- The RuO4-catalyzed ketohydroxylation. Part 1. Development, scope, and limitation
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A new straightforward oxidation of C,C-double bonds to unsymmetrical α-hydroxy ketones using catalytic amounts of RuCl3 and stoichiometric amounts of Oxone under buffered conditions has been developed, a reaction for which we coined the expression "ketohydroxylation". The transformation allows the direct formation of α-hydroxy ketones (acyloins) from olefins without intermediate formation of syn-diols. The present paper will provide detailed information starting with the underlying concept and the subsequent development of the reaction. The effect of base, solvent stoichiometry, and temperature will be discussed resulting in an improved mechanistic model that might help to explain the influence of different reaction parameters on reactivity and selectivity in RuO4-catalyzed oxidations of C,C-double bonds. Furthermore, an improved workup procedure allows the recovery of the ruthenium catalyst by precipitation while simplifying the overall product purification. The second part of the paper focuses on exploration of scope and limitation. A variety of substituted olefins are oxidized to α-hydroxy ketones in good to excellent regioselectivities and yield. Cyclic substrates proved to be problematic to oxidize; however, a careful analysis of temperature effects resulted in the development of a successful protocol for the ketohydroxylation of cyclic substrates by simply decreasing the reaction temperature.
- Plietker, Bernd
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p. 8287 - 8296
(2007/10/03)
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- Samarium diiodide promoted formation of 1,2-diketones and 1-acylamido-2-substituted benzimidazoles from N-acylbenzotriazoles
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N-Acylbenzotriazoles, when treated with samarium diiodide in THF, undergo self-coupling reaction to afford 1,2-diketones in good to excellent yields; while when treated with samarium diiodide in CH3CN, they undergo ring-opening reaction to afford 1-acylamido-2-alkyl (or aryl) benzimidazoles in reasonable to good yields. A plausible mechanism was suggested.
- Wang, Xiaoxia,Zhang, Yongmin
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p. 4201 - 4207
(2007/10/03)
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- RuO4-catalyzed ketohydroxylation of olefins
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A new mild method for the oxidation of a variety of olefins to α-hydroxy ketones is described. Using the concept of a nucleophilic reoxidant, different olefins were ketohydroxylated with high regioselectivity in good to excellent yields.
- Plietker, Bernd
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p. 7123 - 7125
(2007/10/03)
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- Formation of 1,2-diketones by samarium diiodide promoted reaction of N-acylbenzotriazoles
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Transformation of N-acylbenzotriazoles 1 into 1,2-diketones 2 in good to excellent yields has been realized by the use of samarium diiodide at room temperature.
- Wang, Xiaoxia,Zhang, Yongmin
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p. 5431 - 5433
(2007/10/03)
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- Difluoroboroxymolybdenum fischer carbene complexes as precursors of acyl radicals: Dimerization and trapping with electron-deficient alkenes
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Pentacarbonyl acyl molybdates 1 react with boron trifluoride to give difluoroboroxy Fischer carbene complexes 2, which undergo loss of the metal fragment at room temperature to form 1,2-diketones 3, 1,2-hydroxy ketones 4, or dimers 5 through a dimerization or decarbonylation-dimerization process of acyl radicals. Decomposition of 2 in the presence of electron-deficient alkenes 11 and 18 furnishes the two-, three-, and four-component coupling products 12, 13, 19, 20, and 21.
- Barluenga, Jose,Rodriguez, Felix,Fananas, Francisco J.
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p. 1930 - 1937
(2007/10/03)
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- Convenient preparation of metals deposited on solid supports and their use in organic synthesis
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'High-surface alkali metals' can be conveniently prepared via deposition of corresponding metals on various supports such as sodium chloride, polyethylene, polypropylene and cross-linked polystyrene from their solutions in liquid ammonia. Alkali metals deposited on polymeric supports can be stored in form of stable suspensions in inert solvents and used for the acyloin and Dieckmann condensations and for preparation of organolithiums. Addition of the suspension of supported alkali metal to a solution of zinc chloride gave an active zinc on polymeric support, which can be used for the Reformatski and Barbier reactions.
- Majkosza, Mieczyslaw,Nieczypor, Piotr,Grela, Karol
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p. 10827 - 10836
(2007/10/03)
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- Carbonylation of dialkylcyanocuprates with carbon monoxide: Synthesis of α-hydroxyketones
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Dialkylcyanocuprates, prepared from copper(I) cyanide and the corresponding alkyllithium or Gringard reagents, readily react with carbon monoxide in the presence of tri-n-butylphosphine at -78°C in THF to give α-hydroxyketones in high yields (65-85%).
- Kabalka, George W.,Li, Nan-Sheng,Yu, Su
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p. 2203 - 2206
(2007/10/03)
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- Convenient Preparation of 'High-Surface Sodium' in Liquid Ammonia: Use in the Acyloin Reaction
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'Sodium on solid support' (5-20 wt.% of Na on NaCl, glass powder, poly(ethylene) and poly(propylene)) can be conveniently prepared via low-temperature (-33°C) deposition of sodium from its solution in liquid ammonia. Use of this reagent in the acyloin reaction of carboxylic esters gave the corresponding products in good yields.
- Makosza, Mieczyslaw,Grela, Karol
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p. 267 - 268
(2007/10/03)
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- Origin of α-Hydroxy Ketones in the Osmium Tetroxide-Catalyzed Asymmetric Dihydroxylation of Alkenes
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The origin and the mechanism of formation of α-hydroxy ketones in the osmium tetroxide-catalyzed asymmetric cis-dihydroxylation (ADH) of alkenes in the presence of tert-butyl hydroperoxide is described.The formation of α-hydroxy ketones has been established to proceed through either the hydration of monooxobisglycolate ester 2 followed by oxidation with tert-butyl hydroperoxide (TBHP) or by acid-catalyzed addition of TBHP on the intermediate bisglycolate ester 2.On the basis of the mechanistic insight, it has been possible to shut down the formation of α-hydroxy ketones and other side products in the ADH reaction, even when TBHP is used as an oxygen source.It is possible to prepare α-hydroxy ketones in good yields but the optical purity of ketols has been found to be very low, which not only shed significant light on the mechanism of their formation, but also delineated the improbability of syntesizing them in optically active forms by ADH reaction of alkenes.
- Lohray, Braj B.,Bhushan, Vidya,Kumar, R. Krishna
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p. 1375 - 1380
(2007/10/02)
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- The Synthesis of Some Lipophilic Tetradentate Ligands for Use in the Formation of Metal-Linked Polymers
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Two lipophilic tetradentate ligands, 5,5'-di-t-butyl- and 5,5'-dihexyl-2,2'-bipyrimidine, were prepared via either Ullmann or nickel(0)-promoted reactions in low but useful yields.Approaches towards the synthesis of lipophilic ligands based on 2,2'-biimidazole, namely 4,4',5,5'-tetrabutyl-2,2'-biimidazole (from decane-4,5-dione) and various 4,4',5,5'-tetra(arylamino)-2,2'-biimidazoles (from 4,4',5,5'-tetrabromo-2,2'-biimidazole and arylamines), and a 2,2'-bibenzimidazole, 5,5',6,6'-tetra(octyloxy)-2,2'-bibenzimidazole (from N,N'-bisoxamide), were uniformly unsuccessful for preparing the 2,2'-biheteroaryl compounds.
- Crossley, Maxwell J.,Gorjian, Sargon,Sternhell, Sever,Tansey, Kerrie M.
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p. 723 - 738
(2007/10/02)
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- Catalytic action of azolium salts. VI. Preparation of benzoins and acyloins by condensation of aldehydes catalyzed by azolium salts
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Benzoins 4 (2-hydroxyethanones substituted with aryl groups at the 1- and 2-positions) were prepared by self-condensation of aromatic aldehydes 3 using catalytic amounts of azolium salts 1 and 2 in excellent yields. 1,3-Dimethylbenzimidazolium iodide (2) was an effective catalyst for the preparation of acyloins 6 (2-hydroxyethanones substituted with alkyl groups at the 1- and 2-positions) by self-condensation of aliphatic aldehydes 5. On the other hand, an attempt at the condensation of hexanal (5d) catalyzed by 1,3-dimethylimidazolium iodide (1) failed to yield the acyloin 6d, and instead the aldol-type condensed product 8d was obtained.
- Miyashita,Suzuki,Iwamoto,Higashino
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p. 2633 - 2635
(2007/10/02)
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- Ruthenium-Catalyzed Oxidative Transformation of Alkenes to α-Ketols with Peracetic Acid. Simple Synthesis of Cortisone Acetate
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The reactions of alkenes with peracetic acid in the presence of RuCl3 catalyst gave the corresponding α-ketols, which are important building units for synthesis of biological active compounds, such as cortisone acetate.
- Murahashi, Shun-Ichi,Saito, Takao,Hanaoka, Hidenori,Murakami, Yoshihide,Naota, Takeshi,et al.
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p. 2929 - 2930
(2007/10/02)
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- Synthesis of α-Hydroxy Ketones by Direct, Low-Temperature, in Situ Nucleophilic Acylation of Aldehydes and Ketones by Acyllithium Reagents
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The reaction of n-, sec-, and tert-butyllithium with CO at atmospheric pressure at -110 and -135 deg C in the appropriate solvent system in the presence of ketones and aldehydes generates the acyllithium, RC(O)Li, which reacts with the carbonyl compound to give the α-hydroxy ketone, generally in good yield.Reactions with aldehydes are limited in scope, working well with the t-BuLi-derived acyllithium reagents, but not with n-BuC(O)Li.
- Seyferth, Dietmar,Weinstein, Robert M.,Hui, Richard C.,Wang, Wei-Liang,Archer, Colin M.
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p. 5620 - 5629
(2007/10/02)
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- Pulsed-laser photochemistry of pentanal at 355 nm
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Pure pentanal is irradiated with a frequency tripled Nd-YAG laser in the intensity interval 0.1-1 MW. cm-2. Alpha-dione and α-ketol are formed selectively with quantum yields of 5.5 and 38%, respectively. As only the S1 state of the pentanal is excited, the results obtained are explicable as a dynamic effect in connection with the order of the reactions.
- Paquet,Fellous,Stringat,Fabre
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p. 485 - 486
(2007/10/02)
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- Reactivity of a lithium nickel acylate complex in THF
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The reactivity of the lithium salt of a nickel acylate complex in THF is discussed. Upon reaction with a hard acid, this anionic complex oxygen alkylates, forming a nickel carbene complex. This carbene complex reacts with additional acylate complex to generate an enol ether derivative. When the nickel acylate reacts with a soft acid such as an alkyl halide, the intermediate formed is an acyl(alkyl)nickel complex, which very slowly undergoes a reductive elimination. When the nickel acylate complex is oxidized, products consistent with a radical reaction are observed.
- Simunic, Joan L.,Pinhas, Allan R.
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p. 2400 - 2406
(2008/10/08)
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- SILAFUNCTIONAL COMPOUNDS IN ORGANIC SYNTHESIS. 29. OXIDATION OF (ALKENYL)ALKOXYSILANES TO α-HYDROXY KETONES
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(Alkenyl)alkoxysilanes are readily transformed into α-hydroxy ketones via epoxidation and the subsequent oxidative cleavage of the carbon-silicon bonds.
- Tamao, Kohei,Maeda, Kimio
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- Oxidation of hydrocarbons. X. Concerning the formation of ketols and diones during the oxidation of alkenes by permanganate ion
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The oxidation of E-5-decene by potassium permanganate in slightly acidic aqueous acetone solutions has been studied.An analysis of the reaction mixture at various time intervals indicates that the ketol, 5-hydroxy-6-decanone, is the initially formed product under these conditions.The other major product, 5,6-decanedione, is formed sequentially from oxidation of the ketol rather than directly from the alkene.
- Lee, Donald G.,Srinivasan, N. S.
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p. 2146 - 2149
(2007/10/02)
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- Photochemistry in solution-XX. Triplet reactivity of aliphatic aldehydes
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The triplet self-quenching process of three aliphatic aldehydes has been investigated by inhibition with dienes (taking into account the singlet interaction with the dienes) and by laser flash photolysis. The results obtained for intersystem crossing, the setf-quenching process and product formation have been rationalized. The main reactivity observed for the three aldehydes is the self-quenching process which occurs from both the singlet and triplet state. The laser flash photolysis experiments carried out with butanal show two absorptions of a transient at 320 aod 355 nm; no evidence for two different species could be put forward. The similar decay of the two absorption maximas of the transient, as the concentration of aldehyde is increased, would be indicative of only one single absorbing species which could be either the triplet state of the aldehyde or a radical-pair formed by the self-quenching process or the 1,4-biradical resulting from γ-H abstraction. The fact that both the quenching experiments (by dienes or by 1-methylnaphthalene) and the laser flash measurements lead to about the same lifetime also indicates only one species. The products formed from the triplet setf-quenching process have also been obtained by a different method: excitation of benzophenone at 365 nm in the presence of butanal. The quantum yields for product formation is about the same as those obtained for the triplet by direct irradiation of butanal, except that of octane-4,5-dione which is increased if the photoreaction is carried out at 365 nm in the presence of beazophenone.
- Kossanyi,Sabbah,Chaquin,Ronfart-Haret
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p. 3307 - 3315
(2007/10/02)
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