- 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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scheme or table
p. 5382 - 5388
(2011/08/06)
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- Au-catalyzed cyclization of monoallylic diols
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The Ph3PAuCl/AgOTf-catalyzed cyclization of monoallylic diols to form tetrahydropyrans is reported. The reactions proceed rapidly at temperatures as low as -78° C with catalyst loadings as low as 0.1 mol % to provide the products in 79-99% yield. A broad range of structurally diverse substrates perform well in the reaction. When 2,6-disubstituted tetrahydropyrans are produced, the reaction is highly diastereoselective for the 2,6-cis product.
- Aponick, Aaron,Li, Chuan-Ying,Biannic, Berenger
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p. 669 - 671
(2008/09/17)
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- Simplified analogues of qinghaosu (artemisinin)
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Three new simplified analogues of qinghaosu have been designed and synthesized through simple routes without recourse to the commonly employed photosensitized oxidation. The peroxy bonds in the target molecules were taken from UHP with the first peroxy-ca
- Zhang, Qi,Wu, Yikang
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p. 10407 - 10414
(2008/02/12)
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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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- Asymmetric synthesis of myrioxazines A and B, novel alkaloids of Myrioneuron nutans
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Two new epimeric tricyclic alkaloids, myrioxazines A and B were isolated from the leaves of Myrioneuron nutans and their structures elucidated by spectral analysis (mass spectrometry and 2D NMR). Absolute configurations were determined by total asymmetric synthesis.
- Pham, Van Cuong,Jossang, Akino,Chiaroni, Angèle,Sévenet, Thierry,Bodo, Bernard
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p. 7565 - 7568
(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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- Neighboring Group Participation in Lewis Acid-Promoted and Annulations. The Stereocontrolled Synthesis of Tricyclic Ethers
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A variety of 1,4- and 1,5-keto aldehydes derived from cycloalkanes are coupled with the bis(trimethylsilyl) enol ether of methyl acetoacetate in the presence of either TMSOTf or TrSbCl6 to generate tricyclic ethers.The reactions proceed with excellent regiochemical control by a mechanism involving neighboring group participation.This mechanism involves initial formation of a bicyclic oxocarbenium ion intermediate from the keto aldehyde substrates.The geometries of selected bicyclic intermediates have been optimized using the AM1 method allowing successful prediction of the stereochemical outcomes in the cyclization in most cases.Epimerization of α-chiral keto aldehyde substrates does not appear to occur in these Lewis acid-promoted annulation reactions.
- Molander, Gary A.,Cameron, Kimberly O.
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p. 5931 - 5943
(2007/10/02)
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- Intramolecular anodic olefin coupling reactions: The use of bis enol ether substrates
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In an effort to develop electrochemical methods for directly initiating oxidative cyclization reactions, the anodic oxidation of bis enol ether substrates has been examined. The reactions were found to lead to the formation of five-, six-, and seven-membered-ring 1,4-dicarbonyl equivalents. The reactions were not found to be useful for generating larger ring sizes. Both alkyl and silyl enol ether substrates were found to be compatible with the conditions required for carbon-carbon bond formation. Cyclic voltammetry studies indicated that the cyclizations were fast and that the reactions happened at or near the electrode surface. Finally, the cyclization reactions were shown to be compatible with the formation of quaternary carbons, even when carbon-carbon bond formation involved the generation of two vicinal quaternary carbons.
- Moeller, Kevin D.,Tinao, Luzviminda V.
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p. 1033 - 1041
(2007/10/02)
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- WATER-PROMOTED ORGANIC REACTIONS. ALDOL REACTION OF SILYL ENOL ETHERS WITH CARBONYL COMPOUNDS UNDER ATMOSPHERIC PRESSURE AND NEUTRAL CONDITIONS.
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As a consequence of the hydrophobic effect, the reaction between silyl enol ethers and aldehydes are shown to proceed without a catalyst in aqueous solution and neutral conditions providing crossed-aldol products with a syn selectivity, as under pressure, that is the reverse in comparison with the acid catalysed reaction.With α,β-unsaturated aldehydes, 1,2- and 1,4-addition were observed, whereas with α,β-unsaturated ketones, only 1,4-addition occured.
- Lubineau, Andre,Meyer, Elsa
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p. 6065 - 6070
(2007/10/02)
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- Observations sur l'hydrolyse d'acetals dihydropyranniques
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The hydrolysis of of dihydropyranyl acetals by sulfuric acid leads to cyclenones, but by the use of pyridinium p-tolenesulfonate, δ-ketoaldehydes may be isolated.These compounds do not undergo aldol condensation under these conditions.
- Thuy, Vu Moc,Maitte, Pierre
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p. 497 - 499
(2007/10/02)
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- Compounds with Bridgehead Nitrogen. Part 49. The Synthesis and Stereochemistry of Perhydropyridobenzoxazepines and of r-3a,t-11a,c-14a,t-14b,t-22a,t-22b-Perhydrodiquinodioxadiazacyclotetradecine
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Ring closure of the diastereoisomeric 2-decahydroquinolin-8-ylethanols with formaldehyde gave r-4a,c-7a,t-11a-, r-4a,t-7a,t-11a, and r-4a,c-7a,c-11a-perhydropyridobenzoxazepines, but instead of the fourth isomer a dimer, r-3a,t-11a,c-14a,t-14b,t-22a,t-22b-perhydrodiquinodioxadiazacyclotetradecine, was obtained.Comparison of 13C n.m.r. shifts of the conformationally locked isomers with those of perhydropyridooxazepine showed different average perhydro-1,3-oxazepine ring conformations in the various structures so that an estimate of the position of conformational equilibrium (CDCl3 solution) of the bicyclic compound from this data could not be made.The 13C n.m.r. spectrum of perhydropyridooxazepine in CDCl3-CFCl3, however, showed a ratio of ca. 5:1 trans-fused:O-inside-cis-fused conformers at -80 oC.
- Crabb, Trevor A.,Jupp, Philip A.
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p. 913 - 918
(2007/10/02)
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- A New Synthesis of 1,5-Dicarbonyl Compounds under Neutral Conditions
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Michael addition of α-nitroketones to methyl vinyl ketone or acrylaldehyde followed by denitration with Bu3SnH affords 1,5-dicarbonyl compounds in good yields.
- Ono, Noboru,Miyake, Hideyoshi,Kaji, Aritsune
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p. 875 - 876
(2007/10/02)
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- Proton Magnetic Resonance Studies of Compounds with Bridgehead Nitrogen. Part 39. Stereochemistry of Perhydropyrido-benzoxazines and the Conformational Equilibrium for Perhydropyridooxazine
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The four diastereoisomeric perhydropyridobenzoxazines have been synthesised and their configurations assigned by 1H n.m.r. and i.r. spectroscopy and by kinetic studies of N-methylation.Comparisons of the 1H n.m.r. chemical shifts of proton α to nitrogen in these isomers suggested an equilibrium (CDCl3,25 deg C) for perhydropyridooxazine containing ca. 90percent of the trans-fused conformer.
- Crabb, Trevor A.,Turner, Christopher H.
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p. 1778 - 1782
(2007/10/02)
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