Grignard reactions in imidazolium ionic liquids

A new, base-stable, imidazolium room-temperature ionic liquid (RTIL) has been prepared and applied to the addition of Grignard reagents to carbonyl compounds. These reactions occur readily at ambient temperature to afford the alcohol products in good to excellent yield. The RTIL can be recycled and reused numerous times without any difficulty.     

Design of ionic liquids as a medium for the Grignard reaction

Design of novel phosphonium ionic liquids that are compatible with Grignard reagents have been investigated; several types of phosphonium salts that have an alkyl ether moiety have been synthesized and their capability evaluated as solvents for Grignard reagents. It has been established that even basic aliphatic Grignard reagent-mediated reactions are possible when methoxyethyl(tri-n-butyl)phosphonium bis(trifluoromethanesulfonyl)imide is used as the solvent.     

Formation and reactions of alkylzinc reagents in room-temperature ionic liquids

[reaction: see text] The presence of a suitable amount of bromide or chloride ions was found to be critical in forming the alkylzinc reagents from alkyl iodides and zinc metal in the room-temperature ionic liquid, N-butylpyridinium tetrafluoroborate. Beta-hydride transfer in the reactions of butylzinc reagents with aldehydes can also be reduced by a bromide ion.     

Novel organocycloborates via Grignard reagents

An unprecedented cyclisation reaction of alpha,omega-borylbromoalkanes is seen upon treatment with magnesium turnings, forming organocycloborates in high yield. The novel boratacyclopentanes and -hexanes have been characterised by X-ray crystallography.     

Grignard reagents in ionic solvents: electron transfer reactions and evidence for facile Br-Mg exchange

Grignard reagents form persistent solutions in phosphonium ionic liquids possessing O-donor anions and these solutions are excellent reaction media for electron transfer processes and transmetallation reactions.     

The quest for chiral Grignard reagents

The involvement of single electron transfer, i.e. of free radicals in the reactions of organomagnesium reagents could be detected with the aid of a chiral secondary Grignard reagent, in which the magnesium-bearing carbon atom is the sole stereogenic centre. So far, however, such reagents have not been accessible, because the standard preparation of Grignard reagents proceeds via free radicals. We review and summarize here our efforts to generate such a Grignard reagent 36 by asymmetric synthesis starting from an enantiomerically pure alpha-chloroalkyl-sulfoxide 30b using a sulfoxide/magnesium exchange reaction to give 33 followed by a carbenoid homologation reaction. Grignard reagent 36 turned out to be an ideal probe to learn about the extent to which SET is involved in reactions of organomagnesium reagents.     

Dealkylation reactions catalyzed by Grignard reagents

Some reactions of 2,3-dihydrobenzofuran derivatives with Grignard reagents were re-examined in order to account for discrepancies between the yields of starting materials and reaction products. Phenol was found to be present in addition to the products previously described. On the basis of the results it is assumed that phenol results from dealkylation of o-alkylphenol, catalyzed by the magnesium halide moiety of the Grignard reagent.     

Reactions of methylchlorodisilanes with Grignard reagents

Reactions of Cl₂MeSiSiMeCl₂ with RMgCl make it possible to obtain and isolate pure disilanes containing a smaller number of functional groups, namely, RMeClSiSiMeCl₂ (R = Ph), RMeClSiSiMeRCl (R = Prⁱ, Ph), and R₂MeSiSiMeRCl (R = Buⁱ). The reaction of Cl₂MeSiSiMeCl₂ with BuⁿMgCl is the least selective. The chlorides obtained were reduced with LiAlH₄ into the corresponding hydrides.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 954–957, May, 1995.     

Iron-catalyzed alkylation of alkenyl Grignard reagents

The first iron-catalyzed cross-coupling reaction between alkenyl Grignard reagents and n- or s-alkyl bromides is described. The reaction is stereoselective and takes place in the presence of 5 mol % of [Fe(acac)3/TMEDA/HMTA] (1:2:1) under very mild conditions (THF, 0 degrees C, 45 min).     

Highly enantiomerically enriched alpha-haloalkyl Grignard reagents

alpha-Chloro- and alpha-bromoalkyl Grignard reagents 11 and 30 with > 97% ee (enantiomeric excess) were generated by a sulfoxide/magnesium exchange reaction from the enantiomerically and diastereomerically pure sulfoxides 25 and 27. The resulting alpha-haloalkyl Grignard reagents are configurationally stable at -78 degrees C. Racemization sets in at or above -60 degrees C, especially when the solution contains bromide ions. In the absence of halide ions, the configurational stability extends up to -20 degrees C, when chemical decomposition commences.     

Kinetic resolution of racemic Grignard reagents by nickel-catalyzed asymmetric Grignard cross-coupling

Racemic Grignard reagents, 2-phenylpropylmagnesium chloride and 2-norbornylmagnesium chloride were kinetically resolved by asymmetric cross-coupling with vinyl bromides in the presence of chiral phosphine-nickel catalysts to give optically active coupling products (~37% ee) and carboxylic acids after carbonation with carbon dioxide.     

Iron-catalyzed oxidative homo-coupling of aryl Grignard reagents

[reaction: see text] Iron-catalyzed homo-coupling of aryl Grignard reagents was successfully developed. A variety of aryl Grignard reagents were efficiently converted into the corresponding symmetrical biaryls in the presence of 1-5 mol % FeCl3 and a stoichiometric amount of 1,2-dichloroethane.     

Reaction of furfurylidene acetone with Grignard reagents

The interaction of furfurylidene acetone with methylmagnesium iodide and ethylmagnesium halides has been studied. In the first case 2-methyl-4-(2-furyl)-3-buten-2-ol is formed as the product of 1,2-addition (yield 73 %). In the second case 4-(2-furyl)-2-hexanone (42 %) is the result of 1,4-addition, whereas 3-methyl-5-(2-furyl)-3-heptanol (45 %) is formed by consecutive 1,2- and 1,4-addition. In all cases the products of 1,3-addition were found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 921–923, May, 1993.     

Alkenenitriles: annulations with omega-chloro Grignard reagents

[reaction: see text] omega-Chloro Grignard reagents chelate with cyclic gamma-hydroxy-alpha,beta-alkenenitriles to trigger a conjugate addition-alkylation annulation. The chelation-controlled conjugate addition-alkylation is the first anionic annulation with alpha, beta-alkenenitriles, providing cis bicyclo[3.3.0]octane, hydrindane, and decalin ring systems in a single synthetic operation.     

Reactions of Grignard reagents with 1,3-dicyanoadamantane

Reactions of Grignard reagents RMgX (R = Me, Et, Pr, Bu; X = Br, I) with 1,3-dicyanoadamantane (1) were studied. Optimum conditions for the synthesis of monoaddition products of Grignard reagents to compound 1 were established. The first stage of the reaction of cyanoadamantane 1 with MeMgBr was studied by the MNDO-PM3 method. According to calculations, the more preferable reaction mechanism involves formation of a six-membered cyclic intermediate containing two Mg atoms, two C atoms, and one Br and one N atom.     

Kumada-Corriu coupling of Grignard reagents,probed with a chiral Grignard reagent

The Grignard reagent 2, in which the magnesium-bearing carbon atom is the sole stereogenic centre has been coupled with vinyl bromide under Pd(0) or Ni(0)-catalysis to give compound 3 with full retention of configuration. Coupling using Fe(acac)3 or Co(acac)2 as catalyst was accompanied by considerable racemisation. These findings are discussed with respect to a dichotomy between concerted polar and stepwise SET transmetallation pathways.     

Reactions of pentafluorophenylgermanium hydrides with Grignard reagents

Dendritic and cross-linked polyphenylenepolygermanes have been obtained by reactions of EtMgBr with (C₆F₅)₃GeH and (C₆F₅)₂GeH₂, respectively. The reaction of sodium naphthalenide with trihydride C₆F₅GeH₃ gives linear insoluble polymer (C₆F₄GeH₂) _n .Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 191–193, January, 1996.     

Emission-based optical carbon dioxide sensing with HPTS in green chemistry reagents: room-temperature ionic liquids

We describe the characterization of a new optical CO₂ sensor based on the change in the fluorescence signal intensity of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) in green chemistry reagents—room-temperature ionic liquids (RTILs). As far as we are aware, this is the first time RTILs, 1-methyl-3-butylimidazolium tetrafluoroborate (RTIL-I) and 1-methyl-3-butylimidazolium bromide (RTIL-II), have been used as matrix materials with HPTS in an optical CO₂ sensor. It should be noted that the solubility of CO₂ in water-miscible ionic liquids is approximately 10 to 20 times that in conventional solvents, polymer matrices, or water. The response of the sensor to gaseous and dissolved CO₂ has been evaluated. The luminescence intensity of HPTS at 519 and 521 nm decreased with the increasing concentrations of CO₂ by 90 and 75% in RTIL-I and RTIL-II, respectively. The response times of the sensing reagents were in the range 1–2 min for switching from nitrogen to CO₂, and 7–10 min for switching from CO₂ to nitrogen. The signal changes were fully reversible and no significant hysteresis was observed during the measurements. The stability of HPTS in RTILs was excellent and when stored in the ambient air of the laboratory there was no significant drift in signal intensity after 7 months. Our stability tests are still in progress.      

Cooperativity in ionic liquids

Cooperativity in ionic liquids is investigated by means of static quantum chemical calculations. Larger clusters of the dimethylimidazolium cation paired with a chloride anion are calculated within density functional theory combined with gradient corrected functionals. Tests of the monomer unit show that density functional theory performs reasonably well. Linear chain and ring aggregates have been considered and geometries are found to be comparable with liquid phase structures. Cooperative effects occur when the total energy of the oligomer differs from a simple sum of monomer energies. Cooperative effects have been found in the structural motifs examined. A systematic study of linear chains of increasing length (up to nine monomer units) has shown that cooperativity plays a more important role than expected and is stronger than in water. The Cl...H distance of the chloride to the most acidic proton increases with an increasing number of monomer units. The average bond distance approaches 218.9 pm asymptotically. The dipole moment grows almost linearly and the dipole moment per monomer unit reaches the asymptotic value of 16.3 D. The charge on the chloride atoms decreases with an increasing chain length. In order to detect local hydrogen bonding in the clusters a new parametrization of the shared-electron number method is introduced. We find decreasing hydrogen bond energies with an increasing cluster size for both the first hydrogen bond to the most acidic proton and the average hydrogen bond.