- Dichloromethane activation. Direct methylenation of ketones and aldehydes with CH2Cl2 promoted by Mg/TiCl4/THF
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(Chemical Equation Presented) This Mg-TiCl4-promoted CH 2-transfer reaction of CH2Cl2 represents an extremely simple, practical, and efficient methylenation of a variety of ketones and aldehydes, especially in enolizable or sterically hindered ketones such as 2,2-dimethylcyclohexanone, camphor, and fenchone.
- Yan, Tu-Hsin,Tsai, Chia-Chung,Chien, Ching-Ting,Cho, Chia-Ching,Huang, Pei-Chen
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p. 4961 - 4963
(2007/10/03)
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- Dehydration products of 2-methylisoborneol
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2-Methylenebornane and 2-methyl-2-bornene have previously been identified as dehydration or degradation products of 2-methylisoborneol (MIB), a compound responsible for taste and odour problems in various water environments. Previously, the identification of these products has been based on mass spectral analysis only. The dehydration of MIB under a variety of conditions was reinvestigated and the products fully characterised by 1H and 13C n.m.r. and GC-MS. Comparison of EI mass spectra of the dehydration products of MIB with those published previously indicate that earlier assignments of MIB dehydration products are incorrect. 2-Methylenebornane and 2-methyl-2-bornene have previously been identified as dehydration or degradation products of 2-methylisoborneol (MIB), a compound responsible for taste and odour problems in various water environments. Previously, the identification of these products has been based on mass spectral analysis only. The dehydration of MIB under a variety of conditions was reinvestigated and the products fully characterised by 1H and 13C n.m.r. and GC-MS. Comparison of EI mass spectra of the dehydration products of MIB with those published previously indicate that earlier assignments of MIB dehydration products are incorrect.
- Schumann, Russell,Pendleton, Phillip
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p. 1243 - 1246
(2007/10/03)
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- Intermediate phenolic compounds for the catalytic synthesis of chromans
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A catalytic synthesis of chromans in racemic or optically active forms, including intermediates thereto; the synthesis employs an asymmetric palladium (II) catalyzed oxidative cyclization of a 2-homoallylphenol and provides intermediates useful in making chromans, especially vitamin E in racemic or optically active forms.
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- THE WITTIG REACTION USING POTASSIUM-TERT-BUTOXIDE HIGH YIELD METHYLENATIONS OF STERICALLY HINDERED KETONES
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Potassium-tert-butoxide is recommended for general use in Wittig reactions with nonstabilized ylides.High yield methylenations of cyclohexanone and a series of five sterically hindered ketones demonstrate its utility.
- Fitjer, Lutz,Quabeck, Ulrike
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p. 855 - 864
(2007/10/02)
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- Influence of Ring Size on Geminal Interproton Coupling Constants in Exocyclic Methylene Groups
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In systems where substituent effects are constant, there is a well defined trend in the magnitude of geminal interproton coupling constants in exocyclic methylene groups with ring size.Reduction of ring size from six to five to four results in a monotonic reduction in the magnitude of Jgem.These trends apply to methylenecycloalkanes, methylenebenzocycloalkenes and α-methylenecycloalkanones.There is an indication that the trend does not continue for methylenecyclopropanes.A number of new exocyclic-methylene compounds have been designed and synthesized to provide specific experimental data.
- Spear, Robert J.,Sternhell, Sever
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p. 889 - 897
(2007/10/02)
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- THE METHYLENATION OF ENOLIZABLE KETONES AND ESTERS USING ORGANOTITANIUM CHEMISTRY
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The titanium methylidene fragment, Cp2Ti=CH2, resulting from Tebbe's reagent, Cp2TiCH2*AlMe2Cl or the β,β-disubstituted metallacycle, Cp2TiCH2C(Me)(n-Pr)CH2, methylenates enolizable acidic ketones and converts α,α-disubstituted ketones into titanium enolates.The reagent reacts selectively with ketones over esters.
- Clawson, Leigh,Buchwald, Stephen L.,Grubbs, Robert H.
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p. 5733 - 5736
(2007/10/02)
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- Wittig-type Reaction of Dimetallated Carbodianion Species as Produced by Zinc Reduction of gem-Polyhalogen Compounds in the Presence of Levis Acids
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Treatment of R1COR2 with a suspension prepared from diiodomethane, trimethylaluminium and excess zinc in tetrahydrofuran at room temperature affords olefins R1R2C=CH2 in fair (R1,R2=alkyl) to good (R1=alkyl, R2=H) yields.The ketone methylenation is better carried with another system consisting of CH2Br2-Zn-TiCl4.Ketones and aldehydes are transformed into α-chloro α,β-unsaturated esters or α,β-unsaturated esters in good yields on treatment with methyl trichloroacetate or t-butyl dichloroacetate (ethyl dibromoacetate) in the presence of diethylaluminium chloride and zinc.
- Takai, Kazuhiko,Hotta, Yuji,Oshima, Koichiro,Nozaki, Hitosi
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p. 1698 - 1702
(2007/10/02)
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