- CHEMISTRY OF ENOL ETHERS. LXXXVI. DIENE CONDENSATION OF 2-TRIMETHYLSILYLOXY-1,3-DIENES WITH α,β-UNSATURATED ALDEHYDES. 1-FORMYL-4-TRIMETHYLSILYLOXY-3-CYCLOHEXENES AND 1-FORMYL-4-OXOCYCLOHEXANES
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The diene condensation of a series of 2-trimethylsilyloxy-1,3-dienes (2-trimethylsilyloxy-1,3-butadiene, 2-trimethylsilyloxy-1,3-pentadiene, 2-trimethylsilyloxy-4-methyl-1,3-pentadiene) with acrylaldehyde and crotonaldehyde is distinguished by high regioselectivity and low stereoselectivity.The "para" adducts (1-formyl-4-trimethylsilyloxy-3-cyclohexenes) are formed exclusively in all cases, and the reaction leads to the formation of a mixture of the cis and trans isomers with respect to the asymmetric centers.Alcoholysis or acid hydrolysis of 1-formyl-4-trimethylsilyloxy-3-cyclohexenes give high yields of 1-formyl-4-oxocyclohexanes.In a number of cases the diene condensation is accompanied by the formation of undesirable side compounds, produced as a result of transsilylation, which takes place between the 2-trimethylsilyloxy-1,3-diene and crotonaldehyde used in the reaction.
- Makin, S. M.,Shavrygina, O. A.,Nguyen, Fong Tung
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p. 2082 - 2087
(2007/10/02)
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- CONDENSATION OF ETHYL AND METHYL 4-(TRIPHENYLPHOSPHORANYLIDENE)-3-OXOBUTANOATE WITH ENALS
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The manipulation of the mode of reaction of 4-(phosphoranylidene)-3-oxobutanoates with enals and a resulting new synthesis of ethyl β-safranate have been explored.
- Moorhoff, Cornelis M.,Schneider, David F.
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p. 4721 - 4724
(2007/10/02)
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- CHEMISTRY OF ENOL ETHERS. LXII. DIENE CONDENSATION OF 1-TRIMETHYLSILYLOXY-1,3-DIENES WITH α,β-UNSATURATED ALDEHYDES
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The diene condensation of 1-trimethylsilyloxy-1,3-dienes (1-trimethylsilyloxy-1,3-butadiene, 1-trimethylsilyloxy-2-methyl-1,3-pentadiene, 1-trimethylsilyloxy-3-methyl-1,3-butadiene) with α,β-unsaturated aldehydes (acrylic, crotonic) is regioselective, leading to the formation of the "ortho isomers," and the cis-adducts are obtained preferentially.When heated with 10percent hydrochloric acid, the mono- and dimethyl-substituted 1-formyl-2-trimethylsilyloxy-3-cyclohexenes obtained during the diene condensation give high yields of the corresponding substituted 1-formyl-1,3-cyclohexadienes.
- Makin, S. M.,Tung, Nguyen Fyong,Shavrygina, O. A.,Arshava, B. M.,Romanova, I. A.
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p. 640 - 645
(2007/10/02)
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- ELECTROCHEMICAL HYDROXYSELENENYLATION AS A NEW METHOD FOR ONE-STEP PREPARATION OF α-ARYLSELENO-α,β-UNSATURATED ALDEHYDES FROM 3-HYDROXYALKYNES
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Electrochemical oxidation of 3-hydroxyalkynes in the presence of diaryl diselenides in MeCN-H2O provided α-arylseleno-α,β-unsaturated aldehydes 2 in 62-94percent yields via hydroxyselenenylation of alkynes.
- Uneyama, Kenji,Takano, Kunikaju,Torii, Sigeru
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p. 1161 - 1164
(2007/10/02)
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- Diels-Alder Route to Potential Trichothecene Precursors
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2-Methyl-3-yn-2-ol (9) is efficiently converted into 6-formyl-3,6-dimethylcyclohex-2-enyl acetate (4b) and into 6-acetyl-3,6-dimethylcyclohex-2-enyl acetate (4c) via highly regio- and stereo-selective Diels-Alder cycloadditions of 3-methylbuta-1,3-dienyl acetate (2b).The cycloadduct (4b) is converted by base into 4a,5,6,8a-tetrahydro-4a,7-dimethylcoumarin (13b), whilst the cycloadduct (4c) yields 2,3,4a,5,6,8a-hexahydro-2-hydroxy-2,4a,7-trimethylchroman-4-one (15), the structure of which was confirmed by X-ray analysis.Both (13b) and (15) possess a number of structural features of the trichothecenes and may be of value in their total synthesis.
- Banks, Robert E.,Miller, Allen J.,Nunn, John M.,Stanley, Philip,Weakley, Timothy J. R.,Ullah, Zakir
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p. 1096 - 1102
(2007/10/02)
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- Phase-Transfer Catalyzed Reactions. 5. Dramatic Effect of the Concentration of Base on the Dimerization of Crotonaldehyde
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Self-condensation of crotonaldehyde under base-catalyzed phase-transfer conditions leads to aldehydes 3 or 4, depending only on the concentration of aqueous hydroxide used.Quaternary ammonium fluorides in anhydrous THF is shown to be a useful system for conjugate additions involving base-sensitive aldehydes.
- McIntosh, John M.,Khalil, Hamdy,Pillon, David W.
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p. 3436 - 3439
(2007/10/02)
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- Electronic Energy Levels in a Homologous Series of Unsubstituted Linear Polyenes
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Absorption, emission, and exitation spectra of 1,3,5,7-octatetraene, 1,3,5,7,9-decapentaene, and 1,3,5,7,9,11-dodecahexaene have been obtained in room temperature solutions and 77 K glasses.All spectra exibit the chracteristic gap between the origin of the strongly allowed absorption (1Ag --> 1Bu) and the origin of fluorescence (1Ag* --> 1Ag).Comparison with results previously obtained for methyl-substituted polyenes shows that the 1Bu-1Ag* energy gap is a sensitive function of the degree of substitution.Solvent-effects studies have been used to extrapolate transition energies of the unsubstituted polyenes to gas-phase conditions.For the tetraene, pentaene, and hexaene the 1Bu-1Ag* energy differences are 6380, 7050, and 7420 cm-1, respectively.These results are discussed in terms of current theoretical descriptions of polyene electronic states.
- D'Amico, Kevin L.,Manos, Christopher,Christensen, Ronald L.
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p. 1777 - 1782
(2007/10/02)
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