Oxidative Dimerization of Lithium-Enolates of Esters Promoted by TitaniumTetrachloride

Ojima, Iwao; Brandstadter, Stephan M.; Donovan, Robert J.

doi:10.1246/cl.1992.1591

Cited by 24 publications

(23 citation statements)

References 10 publications

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“…[22][23][24][25][26] The best diastereomer ratio (rac and meso ) in the product, which is equal to 89 : 11, is achieved by treat ment of isopentanoic acid enolate with iodine. 26 Since in all other cases 21-25 the content of the rac form of 2,3 di isopropylsuccinate is no more than 70%, this procedure 26 was applied to synthesize the pure racemate of DIPS.…”

Section: Resultsmentioning

confidence: 99%

Stereo- and enantioselective polymerization of hexa-1,5-diene on heterogeneous Ziegler-Natta catalysts obtained with the use of optically active internal donors

Lyubimtsev

Nifant’ev

2009

Russ Chem Bull

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Pure racemates and individual enantiomers of diethyl 2,3 diisopropylsuccinate ((+,-) DIPS and (-) DIPS) and 2,3 diisopropyl 1,4 dimethoxybutane ((+,-) DPDMB and (+) DPDMB) were prepared. The synthesized compounds and diethyl phthalate were used as internal donors for the preparation of heterogeneous Ziegler-Natta catalysts. Polymerization of hexa 1,5 diene was carried out on these catalysts. The obtained samples of poly(methylene 1,3 cyclo pentane) were studied by 13 С NMR spectroscopy and polarimetry. The induction of opti cal activity to polymer is observed with (-) DIPS as the internal donor. The induction value makes up 15-20% from the value recorded in the case of optically active metallocene catalysts. The emergence of induction may be associated with the presence of close contact between the titanium atom and the donor molecule within the active site of catalyst, as well as with the fact that the donor molecule either deactivates a part of the stereospecific titani um centers or influences the structure of the titanium centers during their formation and development.

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Section: Resultsmentioning

confidence: 99%

Stereo- and enantioselective polymerization of hexa-1,5-diene on heterogeneous Ziegler-Natta catalysts obtained with the use of optically active internal donors

Lyubimtsev

Nifant’ev

2009

Russ Chem Bull

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“…We thought that the byproducts might be due to a-elimination of amine hydrogen, yielding an immonium species that can react further. Titanium tetrachloride is known to be able to oxidize electron-rich species such as lithium enolates, 25 possibly analogous to amines. 1,4-Diazabicyclo[2.2.2]octane Dabco and quinuclidine are bridged tertiary amines which cannot undergo a-elimination, because it would form a bridgehead imine in violation of Bredt's rule 26 (Scheme 4).…”

Section: Model Compounds Via Titanium Chloride/tertiary Amines Routementioning

confidence: 99%

Condensation routes to polyaniline and its analogs

Hall

Padías

Boone

2007

J. Polym. Sci. A Polym. Chem.

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To obtain polyanilines which are more structurally perfect than those obtainable by the oxidation of anilines, polycondensation procedures were investigated. Model reactions gave extensive information about yields and about the physical properties of the putative structural polymer units. Condensation of anthraquinones with aromatic diamines using titanium tetrachloride and the unique base, 1,4-diazabicyclo-[2.2.2]-octane Dabco, gave high molecular weight orange polyquinonimines. Alkoxy groups on the anthraquinone ring aided solubility and molecular weight, and appropriately positioned alkoxy groups afforded stereoregular polymers. A bisthiophene benzoquinone also polymerized successfully. Application of the same procedure to 2,5-dimethyl-p-benzoquinone gave stereoregular poly(arylene benzoquinonimines), close analogs of pernigrani line. The factors causing problems in achieving high yields and high molecular weight were identified. Recent synthetic developments in this field are discussed. Reduction of the obtained polyquinonimines proceeded smoothly to the leucoemeraldine analogs. Unlike the results from pernigraniline obtained by oxidative polymerization, no evidence for the formation of the electrically conductive emeraldine form was obtained. Keywords: conducting polymers; conjugated polymers; polyaniline; polycondensation; polyimines H. K. Hall, Jr., received his B.S. at Brooklyn Polytech, M.S. at Pennsylvania State University, and Ph.D. from the University of Illinois in 1949. Postdoctoral work followed, with Prof. P. J. Flory at Cornell and with Professors S. Winstein and W. G. Young at UCLA. After 17 years at DuPont, he moved in 1969 to the University of Arizona. His research interests have included the ring-opening polymerizations of strained bicyclic molecules, the mechanisms of reactions of donor with acceptor olefins, the polymerization of imines, and the synthesis of electrically conductive, piezoelectric, and nonlinear optical polymers.

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“…[iii] They also reported the cross-coupling of two different enolates to generate unsymmetrical 1,4-diketones, but this required the use of one ketone enolate in a three-fold excess over the other. Following these reports, various other oxidants were established for the oxidative coupling of enolates, such as Cu(II) triflate, [iv] Fe(III) chloride, [v] iodine, [vi] Ti(IV) chloride, [vii] and Ag(I) chloride. [ viii] Contemporaneously, the use of non-enolate carbonyl derivatives for oxidative coupling was also pioneered.…”

Section: Introductionmentioning

confidence: 99%

Oxidative Coupling of Enolates, Enol Silanes, and Enamines: Methods and Natural Product Synthesis

2012

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The oxidative coupling of enolates, enol silanes, and enamines provides a direct method for the construction of useful 1,4-dicarbonyl synthons. Despite being first reported in 1935, with subsequent important advances beginning in the 1970’s, the development of this powerful reaction into a reliable methodology was somewhat limited. In recent years, there have been a number of reports from several research groups demonstrating advances in several neglected areas of oxidative coupling. This microreview summarizes these new advances in methodology and provides an overview of recent natural product syntheses that showcase the power of these transformations.

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Oxidative Dimerization of Lithium-Enolates of Esters Promoted by TitaniumTetrachloride

Abstract: Oxidative dimerization of lithium ester enoalates is effectively promoted by TiCl4, which serves as a new and efficient synthetic method. Mechanistic study indicates that the reaction proceeds via a radical-like mechanism, but it is not a free radical process.

Cited by 24 publications

References 10 publications

Stereo- and enantioselective polymerization of hexa-1,5-diene on heterogeneous Ziegler-Natta catalysts obtained with the use of optically active internal donors

Stereo- and enantioselective polymerization of hexa-1,5-diene on heterogeneous Ziegler-Natta catalysts obtained with the use of optically active internal donors

Condensation routes to polyaniline and its analogs

Oxidative Coupling of Enolates, Enol Silanes, and Enamines: Methods and Natural Product Synthesis

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