- Borane-mediated aldol cycloreduction of monoenone monoketones: Diastereoselective formation of quaternary centers
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Exposure of monoenone monoketones to catecholborane in THF at ambient temperature results in tandem 1,4-reduction-aldol cyclization. For aromatic and heteroaromatic enones, six-membered cyclic aldol products are formed in excellent yield with high levels of syn diastereoselectivity. Five-membered ring formation proceeds less readily, but the yield of cyclized product is improved through introduction of Rh(I) salts.
- Huddleston, Ryan R.,Cauble, David F.,Krische, Michael J.
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Read Online
- Asymmetric sequential allylic transfer strategy for the synthesis of (-)-adaline and (-)-euphococcinine
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Enantioselective synthesis of the piperidine alkaloids, (-)-adaline (1) and (-)-euphococcinine (2), were achieved from 7 in a six-step sequence through stepwise allylic transfer reactions. Dramatic additive effect of Bu3SnF for the conversion of 3 into 9 was observed to expedite the process to afford the cyclized products in good yields. Georg Thieme Verlag Stuttgart.
- Lee, Bobin,Kwon, Jisook,Yu, Chan-Mo
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Read Online
- Rhodium-Catalyzed Asymmetric Conjugate Alkynylation/Aldol Cyclization Cascade for the Formation of α-Propargyl-β-hydroxyketones
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A rhodium-catalyzed conjugate alkynylation/aldol cyclization cascade was developed. Densely functionalized cyclic α-propargyl-β-hydroxyketones were synthesized with simultaneous formation of a C(sp)-C(sp3) bond, a C(sp3)-C(sp3) bond, as well as three new contiguous stereocenters. The transformation was achieved with excellent enantio- and diastereoselectivities using BINAP as the ligand. The synthetic utility of the newly installed alkynyl moiety was exhibited by subjecting the products to an array of derivatizations.
- Choo, Ken-Loon,Lautens, Mark
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p. 1380 - 1383
(2018/03/09)
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- Can a Ketone Be More Reactive than an Aldehyde? Catalytic Asymmetric Synthesis of Substituted Tetrahydrofurans
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O-heterocycles bearing tetrasubstituted stereogenic centers are prepared via catalytic chemo- and enantioselective nucleophilic additions to ketoaldehydes, in which the ketone reacts preferentially over the aldehyde. Five- and six-membered rings with both aromatic and aliphatic substituents, as well as an alkynyl substituent, are obtained. Moreover, 2,2,5-trisubstituted and 2,2,5,5-tetrasubstituted tetrahydrofurans are synthesized with excellent stereoselectivities. Additionally, the synthetic utility of the described method is demonstrated with a three-step synthesis of the side chain of anhydroharringtonine.
- Lee, Sunggi,Bae, Han Yong,List, Benjamin
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supporting information
p. 12162 - 12166
(2018/09/11)
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- Palladium-Catalyzed Long-Range Deconjugative Isomerization of Highly Substituted α,β-Unsaturated Carbonyl Compounds
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The long-range deconjugative isomerization of a broad range of α,β-unsaturated amides, esters, and ketones by an in situ generated palladium hydride catalyst is described. This redox-economical process is triggered by a hydrometalation event and is thermodynamically driven by the refunctionalization of a primary or a secondary alcohol into an aldehyde or a ketone. Di-, tri-, and tetrasubstituted carbon-carbon double bonds react with similar efficiency; the system is tolerant toward a variety of functional groups, and olefin migration can be sustained over 30 carbon atoms. The refunctionalized products are usually isolated in good to excellent yield. Mechanistic investigations are in support of a chain-walking process consisting of repeated migratory insertions and β-H eliminations. The bidirectionality of the isomerization reaction was established by isotopic labeling experiments using a substrate with a double bond isolated from both terminal functions. The palladium hydride was also found to be directly involved in the product-forming tautomerization step. The ambiphilic character of the in situ generated [Pd-H] was demonstrated using isomeric trisubstituted α,β-unsaturated esters. Finally, the high levels of enantioselectivity obtained in the isomerization of a small set of α-substituted α,β-unsaturated ketones augur well for the successful development of an enantioselective version of this unconventional isomerization.
- Lin, Luqing,Romano, Ciro,Mazet, Clément
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supporting information
p. 10344 - 10350
(2016/08/31)
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- Transaminase Triggered Aza-Michael Approach for the Enantioselective Synthesis of Piperidine Scaffolds
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The expanding “toolbox” of biocatalysts opens new opportunities to redesign synthetic strategies to target molecules by incorporating a key enzymatic step into the synthesis. Herein, we describe a general biocatalytic approach for the enantioselective preparation of 2,6-disubstituted piperidines starting from easily accessible pro-chiral ketoenones. The strategy represents a new biocatalytic disconnection, which relies on an ω-TA-mediated aza-Michael reaction. Significantly, we show that the reversible enzymatic process can power the shuttling of amine functionality across a molecular framework, providing access to the desired aza-Michael products.
- Ryan, James,?iau?iulis, Mindaugas,Gomm, Andrew,Maciá, Beatriz,O’Reilly, Elaine,Caprio, Vittorio
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supporting information
p. 15798 - 15800
(2016/12/22)
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- Efficient and Selective Cu/Nitroxyl-Catalyzed Methods for Aerobic Oxidative Lactonization of Diols
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Cu/nitroxyl catalysts have been identified that promote highly efficient and selective aerobic oxidative lactonization of diols under mild reaction conditions using ambient air as the oxidant. The chemo- and regioselectivity of the reaction may be tuned by changing the identity of the nitroxyl cocatalyst. A Cu/ABNO catalyst system (ABNO = 9-azabicyclo[3.3.1]nonan-N-oxyl) shows excellent reactivity with symmetrical diols and hindered unsymmetrical diols, whereas a Cu/TEMPO catalyst system (TEMPO = 2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl) displays excellent chemo- and regioselectivity for the oxidation of less hindered unsymmetrical diols. These catalyst systems are compatible with all classes of alcohols (benzylic, allylic, aliphatic), mediate efficient lactonization of 1,4-, 1,5-, and some 1,6-diols, and tolerate diverse functional groups, including alkenes, heterocycles, and other heteroatom-containing groups.
- Xie, Xiaomin,Stahl, Shannon S.
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supporting information
p. 3767 - 3770
(2015/04/14)
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- Proline-Catalyzed Knoevenagel Condensation/[4+2] Cycloaddition Cascade Reaction: Application to Formal Synthesis of Averufin
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A remarkable proline-catalyzed method for the construction of biologically interesting oxygen-bridged tricyclic ketal skeletons was uncovered by starting from a variety of readily available cyclic 1,3-diketones and either 1,4- or 1,5-dicarbonyl substrates. The approach, which mimics a biosynthetic Knoevenagel condensation/[4+2] cycloaddition sequence, establishes a viable synthetic strategy for the efficient formal synthesis of averufin. A remarkable proline-catalyzed Knoevenagel condensation/[4+2] cycloaddition cascade reaction was uncovered for the construction of biologically interesting tricyclic ketal skeletons. This approach mimics a biosynthetic sequence and establishes a viable synthetic strategy for the efficient formal synthesis of averufin.
- Tan, Haibo,Chen, Xinzheng,Chen, Huiyu,Liu, Hongxin,Qiu, Shengxiang
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supporting information
p. 4956 - 4963
(2015/08/03)
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- Ready access to functionally embellished cis -hydrindanes and cis -decalins: Protecting group-free total syntheses of (±)-nootkatone and (±)-Noreremophilane
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A simple and efficient synthesis of functionalized cis-hydrindanes and cis-decalins was achieved using a sequential Diels-Alder/aldol approach in a highly diastereoselective manner. The scope of this method was tested with a variety of substrates and was successfully applied to the synthesis of two natural products in racemic form. The highlights of the present work provide ready access to 13 new cis-hydrindanes/cis-decalins, a protecting group-free total synthesis of an insect repellent Nootkatone, and the first synthesis of a Noreremophilane using the shortest sequence.
- Handore, Kishor L.,Seetharamsingh,Reddy, D. Srinivasa
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p. 8149 - 8154
(2013/09/12)
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- Pyridine is an organocatalyst for the reductive ozonolysis of alkenes
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Whereas the cleavage of alkenes by ozone typically generates peroxide intermediates that must be decomposed in an accompanying step, ozonolysis in the presence of pyridine directly generates ketones or aldehydes through a process that neither consumes pyridine nor generates any detectable peroxides. The reaction is hypothesized to involve nucleophile-promoted fragmentation of carbonyl oxides via formation of zwitterionic peroxyacetals.
- Willand-Charnley, Rachel,Fisher, Thomas J.,Johnson, Bradley M.,Dussault, Patrick H.
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supporting information; experimental part
p. 2242 - 2245
(2012/06/30)
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- Convenient synthesis of non-conjugated alkynyl ketones from keto aldehydes by a chemoselective one-pot nonaflation - Base catalyzed elimination sequence
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Keto aldehydes were selectively converted to non-conjugated alkynyl ketones possessing an unsubstituted alkyne terminus using one-pot nonaflation - base catalyzed elimination reaction sequences. Consecutive one-pot nonaflation of keto aldehydes with perfluorobutane-1-sulfonyl fluoride and elimination of the nonaflyl group using the P1 phosphazene base resulted in the formation of a terminal CC triple bond with the keto group remaining intact. Careful optimization of the reaction conditions enabled a highly chemoselective conversion of the aldehyde function in the presence of unprotected keto groups exploiting a minor difference in acidity of their α-hydrogen atoms. Scope and limitations of the protocol as well as possible implementation of these substrates in Sonogashira coupling were explored.
- Boltukhina, Ekaterina V.,Sheshenev, Andrey E.,Lyapkalo, Ilya M.
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experimental part
p. 5382 - 5388
(2011/08/06)
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- NOVEL COMPOUNDS AS CANNABINOID RECEPTOR LIGANDS
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The present application relates to isothiazolylidene containing compounds of Formula (I) wherein R1, R2, R3, R4, and L are as defined in the specification, compositions comprising such compounds, and methods for treating conditions and disorders using such compounds and compositions.
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Page/Page column 102-103
(2010/06/11)
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- NOVEL COMPOUNDS AS CANNABINOID RECEPTOR LIGANDS
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The present application relates to isothiazolylidene containing compounds of Formula (I) wherein R1, R2, R3, R4, and L are as defined in the specification, compositions comprising such compounds, and methods of treating conditions and disorders using such compounds and compositions.
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Page/Page column 87
(2008/12/08)
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- Intramolecular 1,3-dipolar cycloadditions of dihydroimidazolium ylides: Synthesis of pyrrolo[1,2,3-de]quinoxalines and imidazo[1,2-a]indoles
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N-Alkylation of 4,5-dihydroimidazoles with alkene-containing bromomethyl ketones and treatment of the so-formed 4,5-dihydroimidazolium ions with DBU gives rise to an intramolecular 1,3-dipolar cycloaddition reaction that affords (via a reaction cascade involving eliminative ring-opening, recyclisation and prototropic tautomerism) unexpected hexahydropyrrolo[1,2,3-de]quinoxaline products. Steric bulk in both the dihydroimidazole and the dipolarophile allows isolation of an imidazo[1,2-a]indole, the initial product of cycloaddition. When the bromomethyl ketone contains no other functionality, or when cycloaddition is inhibited due to steric constraints, the dihydroimidazolium ion undergoes ring-opening hydrolysis followed by recyclization of the exposed amino ketone to afford either 3-alkyl-1-formylpiperazine-2-ones or 3-aryl-1-formyl-1,4,5,6- tetrahydropyrazines. The Royal Society of Chemistry 2006.
- Lory, Pedro M.J.,Jones, Raymond C.F.,Iley, James N.,Coles, Simon J.,Hursthouse, Michael B.
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p. 3155 - 3165
(2008/03/12)
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- Samarium diiodide-induced intramolecular pinacol coupling of dinitrones: Synthesis of cyclic cis-vicinal diamines
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Pinacol coupling of alkyl dinitrones mediated by SmI2 was achieved in the presence of a proton source allowing the synthesis of cyclic vicinal diamines with good cis-selectivity. The Royal Society of Chemistry 2005.
- Ebran, Jean-Philippe,Hazell, Rita G.,Skrydstrup, Troels
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p. 5402 - 5404
(2007/10/03)
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- Intramolecular Diels-Alder cycloadditions of fulvenes. Application to the kigelinol, neoamphilectane, and kempane skeletons
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(Chemical Equation Presented) A variety of polycyclic ring skeletons (e.g., kigelinol, neoamphilectane, and kempene systems) can be prepared rapidly via intramolecular Diels-Alder cycloadditions (IMDA) of fulvenes. The length of the tethers and the diversity of the substituents on the fulvene core dictate the nature of the IMDA pathway.
- Hong, Bor-Cherng,Chen, Fon-Len,Chen, Shang-Hung,Liao, Ju-Hsiou,Lee, Gene-Hsiang
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p. 557 - 560
(2007/10/03)
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- Asymmetric syntheses of (1R,1′R,5′R,7′R) and (1S,1′R,5′R,7′R)-1-hydroxy-exo-brevicomin and a formal synthesis of (+)-exo-brevicomin
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Asymmetric syntheses of (1R,1′R,5′R,7′R) and (1S,1′R,5′R,7′R)-1-hydroxy-exo-brevicomins 1 and 2, volatiles of the male mountain pine beetle, and a formal synthesis of (+)-exo-brevicomin 3, a component of the attracting pheromone system of several bark beetles have been achieved. The key steps are Birch reduction of commercially available α-picoline, selective Wittig olefination, and Sharpless asymmetric dihydroxylation.
- Naveen Kumar,Venkateswara Rao
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p. 2227 - 2229
(2007/10/03)
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- Stereocontrol of 1,5-related stereocentres using an intermediate silyl group-the diastereoselectivity of nucleophilic attack on a double bond adjacent to a stereogenic carrying a silyl group
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R-5-Methylcyclohex-2-enone 1 reacts successively with the phenyldimethylsilylzincate reagent and acetaldehyde to give with regiocontrol the aldols 7, dehydration of which creates the E-exocyclic double bond of the α-β-unsaturated ketone 2. Conjugate addition of the ethylcuprate reagent to this compound takes place with high (96 : 4) selectivity in favour of the R stereoisomer 12, hydrolysis of which gives (2R,3R,5S,2′ R)-2-(but-2′-yl)-3-dimethyl(phenyl)silyl-5-methylcyclohexanone 3. The oxime acetate of this ketone undergoes fragmentation in the presence of trimethylsilyl trifluoromethanesulfonate to give 3R,7R,5E-3,7-dimethylnon-5-enonitrile 4, in which an open-chain 1,5-stereo-chemical relationship is set up with a high level of stereocontrol. A similar sequence adding 4-methylpentylcuprate to the enone 2, and fragmentation gives 3R,7R,5E-3,7,11-trimethyldodec-5-enonitrile 20. Reduction and hydrogenation of this nitrile gives 3R,7R-3,7,11 -trimethyldodecanal 22, which can be converted into phytol 25. The ketoaldehyde 29 reacts with samarium iodide to give only the alcohol 30, in which the radical anion has attacked from the top surface, just like the cuprate reagents in their reactions with the ketone 2.
- Fleming, Ian,Maiti, Pranab,Ramarao, Chandrashekar
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p. 3989 - 4004
(2007/10/03)
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- N-phenyl-substituted pyrrolidines, piperidines and azabicyclics by a tandem reduction-double reductive amination reaction
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N-Phenyl-substituted pyrrolidines and piperidines have been synthesized by catalytic reduction of nitrobenzene in the presence of 4- and 5-oxoaldehydes, respectively. The process involves reduction of the aromatic nitro group to give the N-phenylhydroxylamine or aniline followed by reductive amination with the two carbonyl functional groups. Monocyclic systems are generally formed in high yield and are easily purified. The method has also been extended to the synthesis of fused N-phenylazabicyclics from 2-(3-oxopropyl)cycloalkanones. A high degree of diastereoselectivity for the trans-fused product is observed in substrates having an ester group α to the cycloalkanone carbonyl. Bicyclic precursors lacking this ester group give mixtures of cis and trans products. Finally, contrary to previous reports, we have demonstrated that aniline can be substituted for nitrobenzene in these reactions.
- Bunce, Richard A.,Herron, Derrick M.,Lewis, Jason R.,Kotturi, Sharadsrikar V.
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p. 113 - 120
(2007/10/03)
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- Catalytic Conversions in Water. Part 21: Mechanistic Investigations on the Palladium-Catalysed Aerobic Oxidation of Alcohols in Water
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Water-soluble complexes of palladium(II) with phenanthroline-derivatives are stable, recyclable catalysts for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic liquid-liquid system. The active catalyst is a dihydroxy-bridged palladium dimer. Kinetics of the reaction, ligand and anion effects are discussed.
- Ten Brink, Gerd-Jan,Arends, Isabel W. C. E.,Sheldon, Roger A.
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p. 355 - 369
(2007/10/03)
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- Reactions of stabilized Criegee intermediates from the gas-phase reactions of O3 with selected alkenes
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The gas-phase reactions of O3 with 1-octene, trans-7-tetradecene, 1,2-dimethyl-l-cyclohexene, and α-pinene have been studied in the presence of an OH radical scavenger, primarily using in situ atmospheric ionization tandem mass spectrometry (API-MS), to investigate the products formed from the reactions of the thermalized Criege intermediates in the presence of water vapor and 2-butanol (1-octene and trans-7-tetradecene forming the same Criege intermediate). With H3O+(H2O)n as the reagent ions, ion peaks at 149 u ([M + H]+) were observed in the API-MS analyses of the l-octene and trans-7-tetradecene reactions, which show a neutral loss of 34 u (H2O2) and are attributed to the α-hydroxyhydroperoxide CH3(CH2)5CH(OH)OOH, which must therefore have a lifetime with respect to decomposition of tens of minutes or more. No evidence for the presence of α-hydroxyhyroperoxides was obtained in the 1,2-dimethyl-1-cyclohexene or α-pinene reactions, although the smaller yields of thermalized Criegee intermediates in these reactions makes observation of α-hydroxyhydroperoxides from these reactions less likely than from the 1-octene and trans-7-tetradecene reactions. Quantifications of 2,7-octanedione from the 1,2-dimethyl-1-cyclohexene reactions and pinonaldehyde from the α-pinene reactions were made by gas chromatographic analyses during reactions with cyclohexane and with 2-butanol as the OH radical scavenger. The measured yields of 2,7-octanedione from 1,2-dimethyl-1-cyclohexene and of pinonaldehyde from α-pinene were 0.110 ± 0.020 and 0.164 ± 0.029, respectively, and were independent of the OH radical scavenger used. Reaction mechanisms are presented and discussed.
- Baker,Aschmann,Arey,Atkinson
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- Pyrrolo[1,2,3-de]quinoxalines: Unexpected products from 1,3-dipolar cycloaddition of dihydroimidazolium ylides
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4,5-Dihydroimidazoles undergo an N-alkylation and 1,3-dipolar cycloaddition cascade with unsaturated α-bromoketones, with subsequent eliminative ring-opening, recyclisation and tautomerisation to form unexpected hexahydropyrrolo[1,2,3-de]quinoxalines.
- Jones, Raymond C.F,Iley, James N.,Lory, Pedro M.J.,Coles, Simon C.,Light, Mark E.,Hursthouse, Michael B.
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p. 3951 - 3954
(2007/10/03)
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- Stereoselective synthesis of δ-lactones from 5-oxoalkanals via one-pot sequential acetalization, tishchenko reaction, and lactonization by cooperative catalysis of samarium ion and mercaptan
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By the synergistic catalysis of samarium ion and mercaptan, a series of 5-oxoalkanals was converted to (substituted) δ-lactones in efficient and stereoselective manners. This one-pot procedure comprises a sequence of acetalization, Tishchenko reaction and lactonization. The deliberative use of mercaptan, by comparison with alcohol, is advantageous to facilitate the catalytic cycle. The reaction mechanism and stereochemistry are proposed and supported by some experimental evidence. Such samarium ion/mercaptan cocatalyzed reactions show the feature of remote control, which is applicable to the asymmetric synthesis of optically active δ-lactones. This study also demonstrates the synthesis of two insect pheromones, (2S,5R)-2-methylhexanolide and (R)-hexadecanolide, as examples of a new protocol for asymmetric reduction of long-chain aliphatic ketones.
- Hsu,Fang
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p. 8573 - 8584
(2007/10/03)
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- Intramolecular Michael addition of N- and O-centred nucleophiles to tethered acrylates. The role of double-bond geometry in controlling the diastereoselectivity of cyclizations teading to 2,6-disubstituted tetrahydropyrans and piperidines
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The oxyanion derived from hydroxyacrylate E-(5) undergoes smooth intramolecular Michael addition to give the trans-2,6-disubstituted tetrahydropyran (7) as the major product of reaction. In contrast, the oxyanion obtained from isomer Z-(5) cyclizes to give the cis-2,6-disubstituted tetrahydropyran (6) as the major product. Such chemistry has been extended to the enantioselective synthesis of (+)-(6) the acquisition of which constitutes a formal total synthesis of acid (+)-(2), a constituent of the glandular secretion from the civet cat (Viverra civetta). Reductive amination of keto acrylate (12) affords an intermediate amine which cyclizes, in situ, to give the cis-2,6-disubstituted piperidine (26). Analogous treatment of compound (13) delivers the isomeric trans-2,6-disubstituted piperidine (27) as the exclusive product of reaction. Transition state structures have been proposed to account for the diastereoselectivities observed in all of the cyclization reactions.
- Banwell, Martin G.,Bissett, Brett D.,Bui, Chinh T.,Pham, Ha T.T.,Simpson, Gregory W.
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- Intramolecular aldol condensations: Rate and equilibrium constants
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Rate and equilibrium constants have been determined for both the aldol addition and the elimination steps in the intramolecular condensation reactions of 2,5-hexanedione, 2,6-heptanedione, 1-phenyl-1,5-hexanedione, and 5-oxohexanal. The overall thermodynamics are similar for cyclization of 2,5-hexanedione and 2,6-heptanedione; conversion of 2,5-hexanedione to the corresponding enone is actually more favorable, but the cyclization of 2,5-hexanedione is 2400 times slower than that of 2,6-heptanedione. As expected on the basis of intermolecular analogs, the addition step is less favorable and slower for 1-phenyl-1,5-hexanedione, and the addition step for 5-oxohexanal is more favorable though similar in rate to that for heptanedione. Detailed analysis of the kinetics and equilibrium for all of these compounds, as well as 2-(2-oxopropyl)benzaldehyde, in terms of Marcus theory, leads to the same intrinsic barriers for the intramolecular reactions as were seen previously for the intermolecular reactions. This means that rate constants for intramolecular aldol reactions should be predictable from the energetics of the reactions and that the effective molarity can be calculated. Methods for estimating thermodynamic quantities for reactants and products of these reactions have been examined.
- Guthrie,Guo
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p. 11472 - 11487
(2007/10/03)
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- Acid-catalyzed reactions of six- and seven-membered cyclic hemiperacetals and peracetals and of related bicyclic ozonides
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HCl-catalyzed reactions of the hemiperacetals 3-methoxy-3-methyl-7-hydroxy-1,2-dioxepane (1a) and 3-methoxy-3-methyl-6-hydroxy-1,2-dioxane (1b) and of the related ozonides 1-methyl-6,7,8-trioxabicyclooctane (2a) and 1-methyl-5,6,7-trioxabicycloheptane (2b) gave peroxidic monocyclic (11-13), bicyclic (14), and (or) tricyclic (15) products.By contrast, reactions of the peracetals corresponding to 1a and 1b, viz., 3-methyl-3,7-dimethoxy-1,2-dioxepane (13a) and 3-methyl-3,6-dimethoxy-1,2-dioxane (13b) gave only non-peroxide products.Reactions of the persubstituted peracetals 3,6-dimethoxy-3,6-dimethyl-1,2-dioxane (25) and 3,6-dimethoxy-3-isopropyl-6-methyl-1,2-dioxane (27) also gave non-peroxidic products, which resulted from fragmentation of the carbon skeletons.
- Griesbaum, Karl,Kiesel, Gilbert,Mertens, Henri,Krieger-Beck, Petra,Henke, Henning
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p. 2198 - 2204
(2007/10/02)
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- Neighboring group participation in Lewis acid-promoted [3 + 4] and [3 + 5] annulations. The synthesis of oxabicyclo[3.n.1]alkan-3-ones
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Lewis acids are employed as catalysts in the annulation of 1,4- and 1,5-dicarbonyl dielectrophiles with bis(trimethylsilyl) end ethers of β-diketones and β-keto esters. A variety of 2-(alkoxycarbonyl)-m-oxabicyclo[3.n.1]alkan-3-ones can be constructed by this process in which two new carbon-carbon bonds are generated. Unusually high regiocontrol is observed, and good to excellent stereochemical control can be achieved at virtually every position on the new carbocycles. Intramolecular neighboring group participation is proposed to explain the unusually high selectivities attained in the annulation reaction.
- Molander, Gary A.,Camera, Kimberly O.
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p. 830 - 846
(2007/10/02)
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- Direct oxidative cleavage of epoxides to dicarbonyl compounds by ceric ammonium nitrate
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Direct oxidative cleavage of the epoxides (1a-g) with ceric ammonium nitrate in aqueous acetonitrile yields the dicarbonyl compounds (2a-g) in excellent yield.
- Roy, Subhas Chandra,Adhikari, Sankar
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- An intramolecular Baylis-Hillman reaction
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By means of an intramolecular Baylis-Hillman reaction the cyclopentene derivative 1 has been formed from 2. Asymmetric induction is low. In the sixmembered ring example 9 → 10 the yield is only 17% - 23%.
- Roth,Gygax,Frater
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p. 1045 - 1048
(2007/10/02)
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- X = Y - ZH systems as potential 1,3-dipoles part 35. Generation of nitrones from oximes. Class 3 processes. Tandem intramolecular Michael addition (1,3-azaprotio cyclotransfer) - Intermolecular 1,3-dipolar cycloaddition reactions
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Aldoximes and ketoximes possessing γ- or δ-alkenyl substituents undergo thermal conversion to 5-and 6- membered cyclic nitrones via a 1,3-azaprotio cyclotransfer, a 2n + 2oσ + 2π concerted process, rather than a Michael addition. The reactions can be performed as a tandem nitrone formation-cycloaddition sequence or, if required, the intermediate nitrones can be isolated. The cycloadditions usually proceed via an exo-transition state and show both regio- and diastereofacial-specificity. Preliminary attempts at chiral induction via a menthyl auxiliary are reported.
- Grigg, Ronald,Markandu, Jasothara,Perrior, Trevor,Surendrakumar, Sivagnanasundram,Warnock, William J.
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p. 6929 - 6952
(2007/10/02)
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- Ozonolyses of 1-Methylcyclopentene, 1-Methylcyclobutene, 5-Hexen-2-one, and Natural Rubber in the Presence of Methanol
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Ozonolyses of 1-methylcyclopentene (8a) and of 1-methylcyclobutene (8b) in methanol proceeded in each case in the two possible directions.The resulting methoxyperoxides 13 and 14 afforded the corresponding peroxyhemiacetals 15 and 19 by intramolecular reactions of the OOH with the corresponding carbonyl groups.Ozonolysis of 1-methylcyclobutene (8b) additionally gave the corresponding ozonide 17b and 2-hydroperoxy-5-methoxy-2-methyl- as well as 5-hydroperoxy-2-methoxy-2-methyltetrahydrofuran (16b and 18b).The mode of formation of these hydroperoxy compounds has been elucidated by ozonolyses of 5-hexen-2-one (25) and of natural rubber (28) in the presence of methanol. - Keywords: Cycloalkenes, 1-methyl- / Ozonolysis / Peroxyhemiacetals, cyclic / Rubber, natural / Tetrahydrofurans, 2-hydroperoxy-
- Griesbaum, Karl,Kiesel, Gilbert
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p. 145 - 150
(2007/10/02)
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- BIS(TRIMETHYLSILYL) ENOL AS 1,3-DIANON EQUIVALENTS: REGIOCONTROLLED AND ANNULATION REACTIONS
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In the presence of titanium tetrachloride, 1,3-bis(trimethoxysiloxy)-1-methoxy-1,3-butadiene (1) undergoes facile annulation reactions with 1,4 -and 1,5-dielectrophiles to generate seven- and eight-membered bicyclic ether adducts.The annulations occur in good yields (49-83percent) and are also highly regioselective for substrates containing two distinct electrophilic groups.
- Molander, Gary A.,Andrews, Steven W.
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p. 2351 - 2354
(2007/10/02)
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- 1,5-Dicarbonyl Compounds via Michael-Addition of Deprotonated Enamines and Allylamines to 2-(N-Methylanilino) acrylonitrile
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A new method for the synthesis of the title compounds by a onepot, three component, coupling reaction is described.Is consists of the reaction of a homoenolate anion and an enol cation equivalent with subsequent alkylation of an acyl-anion equivalent.Hence the methodology of Umpolung is used in a threefold manner within the reaction sequence.
- Ahlbrecht, Hubertus,Dietz, Manfred,Weber, Lothar
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p. 251 - 254
(2007/10/02)
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- An Asymmetric Synthesis of 2-Substituted Piperidines through Ozonolysis of Cyclopentenes and Reductive Aminocyclization
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By the action of ozone, sodium cyanoborohydride and the optically active benzylic amines 2, the 1-substituted cyclopentenes 1, 5 and 9 were converted to a diastereometric mixture of 1,2-disubstituted piperidines (3, 6 and 10), respectively.Hydrogenation of these compounds and the following work-up yielded optically active 2-alkylpiperidines (4, up to 68percente.e.), pipecolic acid (7, 84percent e.e.) and 2-(hydroxymethyl)piperidine (11, up to 85percente.e.).Chromatographic separation of the major isomers of 3b and 6 enabled optically pure coniine (4b) and pipecolic acid (7) to be prepared, respectively.
- Kawaguchi, Mamoru,Hayashi, Osamu,Sakai, Noriyuki,Hamada, Masayuki,Yamamoto, Yukio,Oda, Jun'ichi
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p. 3107 - 3112
(2007/10/02)
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- Oxidation by cobalt(III)acetate. Part 9. Effect of substituents on the oxidative Cleavage of glycols in acetic acid
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The kinetics of oxidative cleavage of glycols by obalt(III) acetate in acetic acid have been studied.The substrates examined include cis- and trans-cyclopentane- and cyclohexane-1,2-diols and their mono- and dimethyl derivatives.The rates were first-order in both cobalt(III)acetate and substrate in all cases.In the oxidation of five-membered ring diols, cis-diols were generally oxidized faster than the trans-isomers.Complex results were obtained in the case of six-membered ring diols.Thermodynamic parameters were calculated for all the substrates.A mechanism involving a bidente complex of cobalt(III) acetate dimer and glycol is sugge sted, except for the case of trans-cyclopentane-1,2-diols, for which a monodentate intermediate is proposed.
- Gunji, Tomokazu,Hirano, Masao,Morimoto, Takashi
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p. 1827 - 1832
(2007/10/02)
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- PHOTOLYSIS OF SATURATED BICYCLIC PEROXIDES
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Under direct photolysis (n.2.1)-peroxides (n=3-5) isomerise chiefly to epoxyaldehydes, (n.2.2)-peroxides (n=2-4) mainly undergo dehydrogenation to cycloalkane-1,4-diones, and 2,3-dioxabicyclo(2.2.1)heptane exhibits both types of behaviour; photo-isomerisation of 6,7- into 6,8-dioxabicyclooctane occurs when benzophenone is present as sensitiser.
- Bloodworth, A.J.,Eggelte, Henny J.
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p. 1525 - 1528
(2007/10/02)
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- Formation of Dicarbonyl Compounds in the Flash Vacuum Pyrolysis of Saturated Bicyclic Peroxides
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Under flash vacuum pyrolysis, dioxabicycloalkanes (n = 3,4, and 5) isomerise to keto-aldehydes, MeCOnCHO, whereas dioxabicycloalkanes (n = 2,3, and 4) fragment to give, by loss of hydrogen and ethylene, mixtures of cycloalkane-1,4-diones and dialdehydes, OHCnCHO.
- Bloodworth, A. J.,Baker, David S.,Eggelte, Henny J.
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p. 1034 - 1036
(2007/10/02)
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