Grignard Reaction (grignard + reaction)

Distribution by Scientific Domains


Selected Abstracts


A Rapid and Convenient Synthesis of Homoallylic Alcohols by the Barbier,Grignard Reaction.

CHEMINFORM, Issue 7 2005
Grant J. Sormunen
No abstract is available for this article. [source]


Highly Concise Synthesis of 3'-"Up"-ethynyl-5'-methylbicyclo- [3.1.0]hexyl Purine and Pyrimidine Nucleoside Derivatives Using Rhodium(II) Carbenoid Cycloaddition and Highly Diastereoselective Grignard Reaction

CHINESE JOURNAL OF CHEMISTRY, Issue 12 2009
Zunhua Yang
Abstract Synthesis of north -5'-methylbicyclo[3.1.0]hexyl purine and pyrimidine nucleosides with an ethynyl group at C-3' position has been successfully accomplished by a facile method. Methylbicyclo[3.1.0]hexanone (±)- 5 having three contiguous chiral centers was remarkably simply constructed only by four steps containing a carbenoid insertion reaction in the presence of rhodium(II) acetate dimer and CuSO4, giving a correct relative stereochemistry of the generated three chiral centers. Upon Grignard reaction of (±)- 5 with ethynylmagnesium bromide, exclusive diastereoselectivity was observed. Condensation of glycosyl donor (±)- 9 with purine nucleobase afforded only the desired N9 -alkylated nucleoside, while condensation with pyrimidine, N3 -benzoylated uracil gave the desired N1 -alkylated nucleoside (±)- 13 with the undesired O2 -alkylated nucleoside (±)- 14. Probably, (±)- 14 would be formed due to steric hindrance caused upon approaching for N1 -alkylation. [source]


Grignard Reactions in Imidazolium Ionic Liquids.

CHEMINFORM, Issue 43 2006
Scott T. Handy
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


A New Synthetic Route to Unsymmetrical 9-Arylxanthenes,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2009
Sajal Kumar Das
Abstract A facile and general three-step synthetic route towards unsymmetrical 9-arylxanthenes was developed. The reaction sequence involves nucleophilic substitution of commercially available 2-fluorobenzaldehydes with arenoxides, Grignard reaction of the resulting 2-arenoxybenzaldehydes with arylmagnesium bromides, followed by FeCl3 -catalyzed intramolecular diarylmethylation of the resulting carbinols. This strategy was extended to access symmetrical as well as unsymmetrical 9-arylthioxanthenes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


Synthesis of New Thiophene-Substituted 3,3-Diphenyl-3H -naphtho[2,1- b]pyrans by Cross-Coupling Reactions, Precursors of Photomodulated Materials

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2003
Michel Frigoli
Abstract 3,3-Diphenyl-3H -naphtho[2,1- b]pyrans linked to one, two, or three thiophene nuclei in different positions of the naphthalene moiety (5, 6, 8, and 9) by a covalent bond have been prepared in good yields. A Suzuki cross-coupling reaction was used with two possible strategies: chromenization before the coupling with oligothiophenes or chromenization after the coupling, the main intermediates being the diphenyl propargylic alcohol, the functionalized naphthol derivatives, and the thiophenic boronates. The overall yields for obtaining such photochromic compounds are generally quite satisfying. For the 7-position, the coupling reaction has been realized using a Grignard reaction between a tetralone derivative and a thiophenic bromo magnesium intermediate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


Solid-Phase Synthesis of [5.5]-Spiroketals

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2008
Stefan Sommer
Abstract An efficient and reliable multi-step synthesis of 251 natural product-like [5.5]-spiroketals on solid supports has been developed. As central key step, a double intramolecular hetero-Michael (DIHMA) reaction to alkynones was applied. The sequence allows for introduction of numerous substituents on the scaffold and for variation of stereochemistry. [5.5]-Spiroketals bearing an additional ketone were obtained in high overall yields. Further diversification was achieved by reduction of the ketone and reductive amination using polymer-supported borohydride, Grignard reaction and conversion to oxime derivatives in the solution phase. [source]


Convenient methods for the synthesis of d4, d2 and d6 isotopomers of 4-(4-fluorobenzyl)piperidine

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 6 2005
Ágnes Proszenyák
Abstract Pure 4-(4-fluoro-[2,3,5,6- 2H4]benzyl)piperidine was prepared via the Grignard reaction of 4-fluoro-[2,3,5,6- 2H4]bromobenzene and pyridine-4-aldehyde followed by consecutive deoxygenation and heteroatomic ring saturation in the presence of palladium on carbon catalyst. An improved method for the catalytic H/D exchange in benzylic positions of 4-(4-fluorobenzyl)piperidine and its d4 derivative has also been described. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Alkyl halides reactions with cathodes or with magnesium.

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2006
Grignard reagent studied with radical clocks.
Abstract In the mechanism of reaction of Grignard reagent formation for alkyl halides (RX), it is generally assumed that the alkyl radical, formed by the electron transfer from the metal to this halide, reacts rapidly with the paramagnetic MgX, species. The previous comparisons of aryl halides reactivity toward magnesium and their reactivity toward a cathode strongly suggested that MgX, species are not, for the aryl halides, compulsory to rationalise the observed facts. The aryl radicals formed by electron transfer from the metal to the aryl halide would undergo a rapid second electron transfer to yield carbanions transformed into RMgX by reaction with MgX2. In contrast, for the alkyl halides, the reduction of the rapidly formed alkyl radicals into carbanions has seldom been discussed as a possible fate for these radicals, the main discussed fates being dimerisation, disproportionation, hydrogen abstraction from the solvent, rearrangement or coupling with MgX, radicals. Two main differences distinguish the reactivity of alkyl halides from their aryl halides counterpart. First, the radical anions of aryl halides may have a given lifetime whereas electron transfer to alkyl halides is concerted with the cleavage of the molecule. Second, the aryl radicals display far stronger oxidising properties than the alkyl radicals. The counterpart of this property is that aryl carbanions display weaker reducing properties than the alkyl ones. In this report, putting in perspective Grignard reaction and the experimental results obtained with identical radical clocks in electrochemistry, we tentatively provide an answer to the question raised in the title. The comparison of electrochemical patterns of reactivity of selected alkyl halides and the evolutions of yields in the preparation of Grignard reagent suggest a new explanation for the lower yields generally observed when alkyl iodides are the starting substrates. It involves an autocatalytic reaction where carbanionic species formed from the alkyl radicals and diffusing away from the metal surface, transfer one electron to the alkyl halide; the result would be the creation of two radicals leading to an increased amount of by-products. If the carbanionic mechanism were to be retained for the formation of alkyl Grignard reagent one would have to admit that the magnesium surface behaves as a cathode displaying high current densities reminiscent of microelectrodes. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Radical clocks and electron transfer.

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2005
Comparison of crown ether effects on the reactivity of potassium, magnesium towards 1-bromo-2-(3-butenyl)benzene.
Abstract The reaction of the title precursor of the aryl radical clock 1-bromo-2-(3-butenyl)benzene, 1Br, towards potassium and magnesium in THF was studied in the presence and absence of various additives, at ambient and low temperatures. The additives were cis -dicyclohexano-18-crown-6 or tert -butyl alcohol; the first one to render soluble potassium by forming its alkalide, the second to distinguish carbanionic from radical cyclization. The addition of 1Br to a THF stirred suspension of potassium pieces yields remarkably low amounts of products resulting from radical cyclization, in contrast to the amounts reported by Bunnett and Beckwith's group for the reaction in 67% ammonia,33% tert -butyl alcohol medium. The amount of cyclized products obtained with potassium pieces in THF is in the same range as that observed in the reaction of magnesium with 1Br in THF. This similarity allows us to discard the earlier triad hypothesis that we proposed to account for the unexpectedly low amounts of cyclized products of aryl halides radical clocks in Grignard reagent formation. The addition of crown ethers to the THF reaction medium induces contrasting effects for potassium and magnesium. A distinctive increase in the radical cyclization is observed for potassium, whereas the addition of crown inhibits the formation of Grignard reagent more efficiently when the solvent is diethyl ether than when it is THF. The observed effects are explained by putting in perspective the metal reactive dissolution with elementary steps occurring in the vicinity of a cathode. The reaction of potassium pieces or magnesium turnings is comparable to the heterogeneous electron transfer occurring at a cathode whereas the reaction of potassium in the presence of crown ether is comparable to homogeneous conditions of electron transfer obtained in redox catalysis. A discussion of the dianion hypothesis for the Grignard reaction of aryl halides is provided and the importance of considering the reactivity of reactive metal dissolution (or organic corrosion) in the framework of recent progress made in the modelling of electrode reactivity is emphasized. This paper shows that caution should be taken when radical clocks are used to study reactions at the metal,solution interface. More specifically, the non-observation of rearranged products from the radical clock (even for the very rapid ones) under these conditions does not necessary imply that there is no radical intermediate along the dominant reaction channel. This pattern of reactivity strongly contrasts with that usually observed when radical clocks are used in homogeneous media. The leading parameters in the rearranged/unrearranged products ratio seem to be the time that the reactive species (radical anions) created by the first electron transfer spend in the close vicinity of this surface, the rate constant of rearrangement of the radical formed by the cleavage of the radical anion and the redox properties of this radical. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Synthesis and characterization of novel polyimide from bis-(3-aminophenyl)-4-(trifluoromethyl)phenyl phosphine oxide

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2001
Kwang Un Jeong
Abstract A novel diamine, bis-(3-aminophenyl)-4-(trifluoromethyl)phenyl phosphine oxide (mDA3FPPO), containing phosphine oxide and fluorine moieties was prepared via the Grignard reaction from an intermediate, 4-(trifluoromethyl)phenyl diphenyl phosphine oxide, that was synthesized from diphenylphosphinic chloride and 4-(trifluoromethyl)bromobenzene, followed by nitration and reduction. The monomer was characterized by Fourier transform infrared (FTIR), 1H NMR, 31P NMR, 19F NMR spectroscopies; elemental analysis; melting point measurements; and titration and was used to prepare polyimides with a number of dianhydrides such as pyromellitic dianhydride (PMDA), 5,5,-[2,2,2-trifluoro-1-(trifluoromethyl)ethyliden]-bis-1,3-isobenzofuranedione (6FDA), 3,3,,4,4,-benzophenone tetracarboxylic dianhydride (BTDA), and 4,4,-oxydiphthalic dianhydride (ODPA). Polyimides were synthesized via a conventional two-step route; preparation of polyamic acids, followed by solution imidization, and the molecular weight were controlled to 20,000 g/mol. Resulting polyimides were characterized by FTIR, NMR, DSC, and intrinsic viscosity measurements. Refractive-index, dielectric constant, and adhesive properties were also determined. The properties of polyimides were compared with those of polyimides prepared from 1,1-bis-(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (3FDAm) and bis-(3-aminophenyl) phenyl phosphine oxide (mDAPPO). The polyimides prepared from mDA3FPPO provided high glass-transition temperatures (248,311 °C), good thermal stability, excellent solubility, low birefringence (0.0030,0.0036), low dielectric constants (2.9,3.1), and excellent adhesive properties with Cu foils (107 g/mm). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3335,3347, 2001 [source]


Development of an Industrial Multi-Injection Microreactor for Fast and Exothermic Reactions , Part II

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2008
D. M. Roberge
Abstract A Grignard reaction performed in a microreactor is presented. The reaction is of type A (highly exothermic and very rapid) and has a low yield which is attributed to a hot spot formed in the mixing zone of the reactor. The reaction yield could be significantly increased by applying the multi-injection principle, leading to better thermal control in the microreactor. Nevertheless, the microreactor plays a major role in reducing the magnitude of the hot spot. Knowing this, it was possible to design and construct an industrial microreactor with significant advantages such as modularity, high flow rate operation, and low investment expenditure (pumps and flow controller minimization). [source]


Highly Concise Synthesis of 3'-"Up"-ethynyl-5'-methylbicyclo- [3.1.0]hexyl Purine and Pyrimidine Nucleoside Derivatives Using Rhodium(II) Carbenoid Cycloaddition and Highly Diastereoselective Grignard Reaction

CHINESE JOURNAL OF CHEMISTRY, Issue 12 2009
Zunhua Yang
Abstract Synthesis of north -5'-methylbicyclo[3.1.0]hexyl purine and pyrimidine nucleosides with an ethynyl group at C-3' position has been successfully accomplished by a facile method. Methylbicyclo[3.1.0]hexanone (±)- 5 having three contiguous chiral centers was remarkably simply constructed only by four steps containing a carbenoid insertion reaction in the presence of rhodium(II) acetate dimer and CuSO4, giving a correct relative stereochemistry of the generated three chiral centers. Upon Grignard reaction of (±)- 5 with ethynylmagnesium bromide, exclusive diastereoselectivity was observed. Condensation of glycosyl donor (±)- 9 with purine nucleobase afforded only the desired N9 -alkylated nucleoside, while condensation with pyrimidine, N3 -benzoylated uracil gave the desired N1 -alkylated nucleoside (±)- 13 with the undesired O2 -alkylated nucleoside (±)- 14. Probably, (±)- 14 would be formed due to steric hindrance caused upon approaching for N1 -alkylation. [source]