Mechanism of the reaction of acetylene with Grignard reagents

Kinetics of the reaction between acetylene and phenylmagnesium bromide were investigated in diethyl ether in the presence of small additions of triethylamine and without a catalyst. The mechanistic scheme suggested by Grignard et al. was supplemented with the reaction of bromomagnesiumacetylene with the Grignard reagent. The rate constants for individual reactions were determined. Triethylamine catalyzes the reactions to different extents, the conversions of bromomagnesiumacetylene being the most susceptible to the catalysis. The possible ways of the action of the catalyst were discussed and the importance of nucleophilic assistance was stressed.     

Nickel-catalyzed cross-coupling reaction of alkynyl bromides with Grignard reagents

We describe a convenient method for the synthesis of 1,2-disubstituted acetylenes via a cross-coupling reaction of （bromoethynyl）benzene with Grignard reagents. The reaction of （bromoethynyl）benzene （1 mmol） with Grignard reagent （1.3 mmol） mediated by NiCl2 （4 mol%） and （p-CH3Ph）3P （8 mol%） in THF could produce 1,2-disubstituted acetylenes in good yields at room temperature.     

Ni- or Cu-catalyzed cross-coupling reaction of alkyl fluorides with Grignard reagents

n-Octyl fluoride underwent a cross-coupling reaction with n-propylmagnesium bromide in the presence of 1,3-butadiene using NiCl2 as a catalyst at room temperature to give undecane in moderate yields. This alkyl-alkyl cross-coupling proceeded more efficiently when CuCl2 was employed instead of NiCl2. Addition of 1,3-butadiene dramatically improved the yields of the coupling products from primary alkyl Grignard reagents in both Ni- and Cu-catalyzed reactions. Alkyl fluorides efficiently reacted with tertiary alkyl and phenyl Grignard reagents using CuCl2 in the absence of 1,3-butadiene to afford the coupling products in high yields. The competitive reaction of a mixture of alkyl halides (R-X; X = F, Cl, Br) with nC5H11MgBr showed that the reactivities of the halides increase in the order R-Cl < R-F < R-Br. In contrast, in the Cu-catalyzed reaction with PhMgBr, the reactivities increase in the order R-Cl < R-Br < R-F.     

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.     

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.     

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.     

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.     

Manganese-catalyzed cross-coupling reaction between aryl Grignard reagents and alkenyl halides

Aryl Grignard reagents react stereospecifically with alkenyl halides in the presence of manganese chloride (10%) to afford good yields of cross-coupling products.     

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.     

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.     

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.     

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.     

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.     

Synthesis of carboxylic amides by ring-opening of oxazolidinones with Grignard reagents

Treatment of N-alkyl-oxazolidin-2-ones with Grignard reagents gives tertiary carboxylic amide products. Various substituted oxazolidinones can be used as illustrated with phenyl, benzyl or isopropyl groups on the 4-position, and methyl, benzyl or p-methoxybenzyl groups on the 3-position (the nitrogen atom). A selection of Grignard reagents were successful, including allyl, benzyl, alkyl and phenyl magnesium halides. The organomagnesium species attacks the carbonyl group and promotes ring-opening of the oxazolidinone. The product tertiary amides are useful substrates for stereoselective transformations and were applied to a highly selective enolate alkylation and to a ring-closing metathesis reaction to a six-membered lactam and hence a formal synthesis of the alkaloids (-)-coniine and (+)-stenusine.