- Ruthenium-lewis acid catalyzed asymmetric diels-alder reactions between dienes and α,β-unsaturated ketones
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The complex [Ru(Cp)(R,R-BIPHOP-F)(acetone)][SbF6],(R,R)-1a. was used as catalyst for asymmetric Diels-Alder reactions between dienes (cyclopentadiene, methylcyclopentadienc, isoprene, 2,3-dimethylbutadiene) and α,β-unsaturated ketones (methyl vinyl ketone (MVK). ethyl vinyl ketone, divinyl ketone, α-bromovinyl methyl ketone and α-chlorovinyl methyl ketone). The cycloaddition products were obtained in yields of 50-_90% and with enantioselectivities up to 96% ee. Ethyl vinyl ketone, divinyl ketone and the halogenated vinyl ketones worked best and their reactions with acyclic dienes consistently provided products with >90% ee. α-Chlorovinyl methyl ketone performed better than α-bromovinyl methyl ketone. The reaction also provided a [4.3.1]bicyclic ring system in 95% ee through an intramolecular cycloaddition reaction. Crystal structure determinations of [Ru(Cp)((S,S)-BIPHOP-F)(mvk)]-[SbF6], (S,S)-1b, and [Ru(Cp)((R,R)-Me4BIPHOP-F)(acrolein)][SbF6], (R,R)-2b, provided the basis for a rationalization of the asymmetric induction.
- Rickerby, Jenny,Vallet, Martial,Bernardinelli, Gerald,Viton, Florian,Kuendig, E. Peter
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p. 3354 - 3368
(2008/03/27)
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- Chlorination of α,β-Unsaturated Ketones and Esters in the Presence of Acid Scavengers
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The chlorination of a series of α,β-unsaturated ketones and esters by Cl2 in CH3OH, with and without acid scavengers such as N-chlorosuccinimide (NCS), pyridine and 2,6-lutidine, is described.Methyl vinyl ketone and cyclohex-2-enone have also been chlorinated in ethanol.Mixtures of Markovnikov(M) and anti-Markovnikov(AM) methoxy chlorides and dichlorides are formed in most cases; phenyl vinyl ketone gives no M products in the absence of pyridine, M methoxy chloride is not formed with (E)-4-chlorobut-3-en-2-one under any conditions, pyridine has no effect on the product ratios and methyl 3-chlorobut-2-enoate forms only dichloride.Chlorination of the ketones in the presence of the pyridines results in a significant increase in the M regioisomer (except for methyl isopropenyl ketone and the ketones mentioned), giving M : AM ratios which are similar to the corresponding esters.Ratios for the esters are not affected significantly by pyridine.We ascribe the effect of the pyridine bases to the elimination of acid and the acid-catalysed mechanism, permitting the chlorination to occur via a carbon-carbon ?-bond (chloronium ion) mechanism.The rate of chlorination of methyl vinyl ketone is retarded by pyridine but is still considerably faster than methyl acrylate.NCS, in contrast to N-bromosuccinimide (NBS) reported previously, has no effect on the M : AM ratio.The chlorination of methyl vinyl ketone with NCS and HCl gives markedly different results from Cl2.
- Heasley, Victor L.,Elliott, Stephen L.,Erdman, Paul E.,Figueroa, Daphne E.,Krosley, Kevin W.,et al.
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p. 393 - 399
(2007/10/02)
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- Yeast Reduction of Some Four-Carbon Chlorinated Ketones. A Convenient Synthesis of (S)-(+)-But-3-en-2-ol
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The action of fermenting yeast on various four-carbon chlorinated ketones has been studied. (S)-(+)-But-3-en-2-ol is conveniently prepared from (+/-)-3-chlorobutan-2-one which yields a 1:1 mixture of (2S,3S)- and (2S,3R)-3-chlorobutan-2-ols.Conversion of the mixture into the dimethyl-methoxymethyl ethers followed by dehydrohalogenation and hydrolysis then gives (S)-(+)-but-3-en-2-ol.
- Ibrahim, Tuncel,Grattan, Timothy J.,Whitehurst, John Stanley
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p. 3317 - 3319
(2007/10/02)
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- CAPTODATIVE SUBSTITUENT EFFECTS XXI. SYNTHESIS OF SELENENYLATED CAPTODATIVE OLEFINS VIA SELENENYL HALIDE ADDITION TO OLEFINS BEARING ELECTRON-WITHDRAWING SUBSTITUENTS
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Addition of methane- and benzeneselenenyl bromide or chloride and benzene sulfenyl chloride to carbon-carbon double bonds substituted by electron-withdrawing groups is achieved in solvents of different polarity.Two regioisomeric adducts 6 and 7 or 8 and 9 are generally formed, which can be interconverted by equilibration in refluxing acetonitrile.It is of mechanistic interest that the regioisomers may also derive from selenenyltrihalide adducts.In comparison to acrylic esters, the propiolic ester reacts more slowly, producing mainly the α-selenenyl adduct.Dehydrohalogenation of adducts provides a general and valuable method for the preparation of olefins carrying methyl or phenylselenyl groups in α-position to electron-withdrawing substituents.
- Piettre, S.,Janousek, Z.,Merenyi, R.,Viehe, H. G.
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p. 2527 - 2544
(2007/10/02)
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- REACTION OF HALOGENS WITH SOME α,β-UNSATURATED ALDEHYDES AND KETONES
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Mechanisms are proposed to acconunt for evidence indicating that some simple α,β-unsaturated aldehydes and ketones do not react with halogens by the expected attack on the C=C bond.
- Heasley, Victor L.,Shellhamer, Dale F.,Carter, Tom L.,Gipe, Daphne E.,Gipe, Robert K.,et al.
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p. 2467 - 2470
(2007/10/02)
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- Dienylphosphates
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Dienylphosphates of the formula SPC1 Wherein each of R1 and R1 ' is lower alkyl, aryl or benzyl and each of R2, R3 and R4 is hydrogen or lower alkyl, Are useful as anthelmintic agents and as intermediates for enolphosphates having anthelmintic activity.
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