Secondary Alkyl Grignard Reagents Research Articles

Desymmetrization of Inert meso-Diethers through Copper-Catalyzed Asymmetric Allylic Alkylation with Grignard Reagents.

We have developed a highly regio-, diastereo-, and enantioselective Cu-catalyzed desymmetrization of inert meso-diethers using Grignard reagents. Moreover, previous inaccessible sterically hindered organometallic reagents are realized in the reaction with broad secondary alkyl Grignard reagents. Finally, detailed control experiments and density functional theory calculations revealed the desymmetrization of meso-diethers exploits a direct anti-SN2' pathway, in the absence of an in situ-generated allyl bromine intermediate. The following oxidative addition is the crucial rate-determining and enantioselectivity-determining step.

Purple Light-Promoted Coupling of Bromopyridines with Grignard Reagents via SET.

Alkyl- and arylpyridines and 2,2'-bipyridines are conventionally prepared by Minisci reactions of pyridines and transition metal-catalyzed coupling reactions of halopyridines. Herein, purple light-promoted radical coupling reactions of 2- or 4-bromopyridines with Grignard reagents in Et2O or a mixture of Et2O and tetrahydrofuran in regular glassware without the need for a transition metal catalyst were disclosed for the first time. Methyl, primary and secondary alkyl, cycloalkyl, aryl, heteroaryl, pyridyl, and alkynyl Grignard reagents were compatible with the protocol. As a result, alkyl- and arylpyridines and 2,2'-bipyridines were easily prepared. Single electron transfer from the Grignard reagent to bromopyridine was stimulated by purple light. An electron extruded from the dimerization of the Grignard reagent worked as the catalyst. Light on/off experiments indicated that constant irradiation was required for product formation. Studies of radical clock substrates verified the involvement of a pyridyl radical from bromopyridine and the noninvolvement of an alkyl or aryl radical from the Grignard reagent. The available proof supports a photoinduced SRN mechanism for the new coupling reactions.

Cu-mediated or metal-free alkylation of gem-dibromoalkenes with tertiary, secondary and primary alkyl Grignard reagents

Abstract A novel copper-mediated or transition-metal-free alkylation of gem-dibromoalkenes with tertiary, secondary and primary alkyl Grignard reagents was described. The outcomes of these reactions were found to be highly dependent on the reaction conditions and the type of Grignard reagents used. Specifically, the tertiary alkylation of gem-dibromoalkenes proceeded efficiently in the presence of 50 mol% CuCN or under transition-metal-free conditions, furnishing the tertiary alkyl-substituted monobromoalkenes or alkenes in high yields.

C-F Activation for C(sp2)-C(sp3) Cross-Coupling by a Secondary Phosphine Oxide (SPO)-Nickel Complex.

A secondary phosphine oxide (SPO)-nickel catalyst allowed the activation of otherwise inert C-F bonds of unactivated arenes in terms of challenging couplings with primary and secondary alkyl Grignard reagents. The C-F activation is characterized by mild reaction conditions and high levels of branched selectivity. Electron-rich and electron-deficient arenes were suitable electrophiles for this transformation. In addition, this strategy also proved suitable to heterocycles and for the activation of C-O bonds under slightly modified conditions.

Nickel-Catalyzed Alkylation or Reduction of Allylic Alcohols with Alkyl Grignard Reagents.

By choosing different phosphine ligands, nickel-catalyzed selective alkylation and reduction of allylic alcohols with alkyl Grignard reagents were performed. The reaction using Ni(dppe)Cl2 as the catalyst resulted in the cross-coupling of allylic alcohols with primary alkyl Grignard reagents and cyclopropylmagnesium bromide. The reaction catalyzed by the combination of Ni(PCy3)2Cl2 and dcype led to the reduction of allylic alcohols. Secondary alkyl Grignard reagents except cyclopropylmagnesium bromide always led to reduction of allylic alcohols using either Ni(dppe)Cl2 or Ni(PCy3)2Cl2/dcype as the catalyst. In the reductive reaction β-H-containing alkyl Grignard reagents were required.

Nickel‐Catalyzed C(sp2)−C(sp3) Kumada Cross‐Coupling of Aryl Tosylates with Alkyl Grignard Reagents

AbstractAryl tosylates are an attractive class of electrophiles for cross‐coupling reactions due to ease of synthesis, low price, and the employment of C−O electrophiles, however, the reactivity of aryl tosylates is low. Herein, we report the Ni‐catalyzed C(sp2)−C(sp3) Kumada cross‐coupling of aryl tosylates with primary and secondary alkyl Grignard reagents. The method delivers valuable alkyl arenes by cross‐coupling with challenging alkyl organometallics possessing β‐hydrogens that are prone to β‐hydride elimination and homo‐coupling. The reaction is catalyzed by an air‐ and moisture stable‐Ni(II) precatalyst. A broad range of electronically‐varied aryl tosylates, including bis‐tosylates, underwent this transformation, and many examples are suitable at mild room temperature conditions. The combination of Ar−X cross‐coupling with the facile Ar−OH activation/cross‐coupling strategy permits for orthogonal cross‐coupling with challenging alkyl organometallics. Furthermore, we demonstrate that the method operates with TON reaching 2000, which is one of the highest turnovers observed to date in Ni‐catalyzed cross‐couplings.magnified image

Copper- and Nickel-Catalyzed Cross-Coupling Reaction of Monofluoroalkenes with Tertiary, Secondary, and Primary Alkyl and Aryl Grignard Reagents

A highly efficient cross-coupling reaction of monofluoroalkenes with tertiary, secondary, and primary alkyl and aryl Grignard reagents in the presence of a catalytic amount of copper or nickel catalyst, respectively, has been developed. The reactions proceeded smoothly at room temperature, providing (E)-alkene isomers in moderate to high yields. Plausible mechanisms of the Ni-catalyzed coupling reaction of monofluoroalkene with Grignard reagents are suggested.

ChemInform Abstract: Zirconocene‐Mediated Carbonylative Coupling of Grignard Reagents.

AbstractThe transmetalation of Grignard reagents with zirconocene dichloride under a CO atmosphere generates acyl zirconium(IV) complexes that are inaccessible with the Schwartz reagent, including those derived from secondary and tertiary alkyl and aryl Grignard reagents.

Sterically Controlled Cu-Catalyzed or Transition-Metal-Free Cross-Coupling of gem-Difluoroalkenes with Tertiary, Secondary, and Primary Alkyl Grignard Reagents.

A robust copper-catalyzed or transition-metal-free cross-coupling of gem-difluoroalkenes with tertiary, secondary, and primary alkyl Grignard reagents has been developed. Remarkably, the tertiary and secondary alkylation of gem-difluoroalkenes proceeded very smoothly in the presence of 25 mol % of CuCN or under transition-metal-free conditions, affording the tertiary and secondary alkyl-substituted fluoroalkenes in good to excellent yields with excellent Z stereoselectivity.

Zirconocene‐Mediated Carbonylative Coupling of Grignard Reagents

AbstractOrganozirconocenes are versatile synthetic intermediates that can undergo carbonylation to yield acyl anion equivalents. Zirconocene hydrochloride ([Cp2ZrHCl]) is often the reagent of choice for accessing these intermediates but generates organozirconocenes only from alkenes and alkynes. This requirement eliminates a broad range of substrates. For example, organozirconocenes in which the zirconium center is bonded to an aromatic ring, a benzylic group, or an alkyl group that possesses a tertiary or quaternary carbon atom α to the carbon–zirconium bond can not be formed in this way. To provide more generalized access to acyl zirconium reagents, we explored the transmetalation of Grignard reagents with zirconocene dichloride under a CO atmosphere. This protocol generates acyl zirconium(IV) complexes that are inaccessible with the Schwartz reagent, including those derived from secondary and tertiary alkyl and aryl Grignard reagents.

Zirconocene-Mediated Carbonylative Coupling of Grignard Reagents.

Organozirconocenes are versatile synthetic intermediates that can undergo carbonylation to yield acyl anion equivalents. Zirconocene hydrochloride ([Cp2 ZrHCl]) is often the reagent of choice for accessing these intermediates but generates organozirconocenes only from alkenes and alkynes. This requirement eliminates a broad range of substrates. For example, organozirconocenes in which the zirconium center is bonded to an aromatic ring, a benzylic group, or an alkyl group that possesses a tertiary or quaternary carbon atom α to the carbon-zirconium bond can not be formed in this way. To provide more generalized access to acyl zirconium reagents, we explored the transmetalation of Grignard reagents with zirconocene dichloride under a CO atmosphere. This protocol generates acyl zirconium(IV) complexes that are inaccessible with the Schwartz reagent, including those derived from secondary and tertiary alkyl and aryl Grignard reagents.

Alkyl Grignard cross-coupling of aryl phosphates catalyzed by new, highly active ionic iron(ii) complexes containing a phosphine ligand and an imidazolium cation.

A novel family of ionic iron(ii) complexes of the general formula [HL][Fe(PR'3)X3] (HL = 1,3-bis(2,6-diisopropylphenyl)imidazolium cation, HIPr, R' = Ph, X = Cl, 2; HL = HIPr, R' = Cy, X = Cl, 3; HL = HIPr, R' = Ph, X = Br, 4; HL = HIPr, R' = Cy, X = Br, 5; HL = 1,3-bis(2,4,6-trimethylphenyl)imidazolium cation, HIMes, R' = Cy, X = Br, 6) was easily prepared via a stepwise approach in 88%-92% yields. In addition, an ionic iron(ii) complex, [HIPr][Fe(C4H8O)Cl3] (1), has been isolated from the reaction of FeCl2(THF)1.5 with one equiv. of [HIPr]Cl in 90% yield and it can further react with one equiv. of PPh3 or PCy3, affording the corresponding target iron(ii) complex 2 or 3, respectively. All these complexes were characterized by elemental analysis, electrospray ionization mass spectrometry (ESI-MS), 1H NMR spectroscopy and X-ray crystallography. These air-insensitive complexes 2-6 showed high catalytic activities in the cross-coupling of aryl phosphates with primary and secondary alkyl Grignard reagents with a broad substrate scope, wherein [HIPr][Fe(PCy3)Br3] (5) was the most effective. Complex 5 also catalyzes the reductive cross-coupling of aryl phosphates with unactivated alkyl bromides in the presence of magnesium turnings and LiCl, as well as the corresponding one-pot acylation/cross-coupling sequence under mild conditions.

Iron Fluoride/N-Heterocyclic Carbene Catalyzed Cross Coupling­ between Deactivated Aryl Chlorides and Alkyl Grignard Reagents with or without β-Hydrogens

High-yielding cross-coupling reactions of various combinations of aryl chlorides and alkyl Grignard reagents have been developed by using an iron(III) fluoride/1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (SIPr) catalyst composite. The iron(III) fluoride/SIPr-catalyzed aryl–alkyl coupling demonstrates unprecedented scope for both aryl chlorides and alkyl Grignard reagents, thus enabling the first efficient coupling of electron-rich (deactivated) aryl chlorides with alkyl Grignard­ reagents without β-hydrogens. The present reaction is also effective for diverse alkyl Grignard reagents such as (trimethylsilyl)methyl, primary, and secondary alkyl Grignard reagents.

ChemInform Abstract: Iron‐Catalyzed Cross‐Coupling of Aryltrimethylammonium Triflates and Alkyl Grignard Reagents.

Abstract Fe(acac)3 effectively catalyzes reaction of aryltrimethylammonium triflates with β-hydrogen-containing primary or secondary alkyl Grignard reagents in a mixed solvent of THF and NMP at room temperature. A series of functional groups are tolerated under the reaction conditions.

Iron-catalyzed cross-coupling of aryltrimethylammonium triflates and alkyl Grignard reagents

Fe(acac)3 effectively catalyzes reaction of aryltrimethylammonium triflates with β-hydrogen-containing primary or secondary alkyl Grignard reagents in a mixed solvent of THF and NMP at room temperature. A series of functional groups are tolerated under the reaction conditions.

ChemInform Abstract: Nickel‐Catalyzed Coupling of Thiomethyl‐Substituted 1,3‐Benzothiazoles with Secondary Alkyl Grignard Reagents.

AbstractThiazoles (VI) and (VII) fail to react.

ChemInform Abstract: Copper‐Catalyzed Cross‐Coupling of Functionalized Alkyl Halides and Tosylates with Secondary and Tertiary Alkyl Grignard Reagents.

Added value: A copper-based method is highly efficient for the cross-coupling of alkyl electrophiles with secondary and tertiary alkyl Grignard reagents. The method is distinguished by its broad substrate scope and high functional group tolerance.

Nickel‐Catalyzed Coupling of Thiomethyl‐Substituted 1,3‐Benzothiazoles with Secondary Alkyl Grignard Reagents

Transition-metal catalyzed CC bond-forming reaction is a useful and straightforward method for the functionalization of azole heterocycles, [1] which are frequently found as key frameworks in natural products, pharmaceutics, and organic functional materials. [2a] Because the C2 position of 1,3azoles, such as oxazoles, thiazoles, and imidazoles, in many natural and synthetic compounds are alkylated, [2b–g] the development of simple and efficient methods for introducing an alkyl group in this position would be highly desirable for the synthesis of these compounds. The conventional reaction for the alkylation of 1,3-azoles includes the coupling of 2metalated azoles generated beforehand or in situ from the parent unsubstituted 1,3-azole under basic conditions with alkyl electrophiles (Scheme 1, path A) [3, 4] and the coupling

ChemInform Abstract: Copper‐Catalyzed Cross‐Coupling of Nonactivated Secondary Alkyl Halides and Tosylates with Secondary Alkyl Grignard Reagents.

AbstractA general approach is given for the cross coupling reaction of secondary tosylates and bromides with secondary alcohols [→ (III), (V), (VIIb)].

ChemInform Abstract: An Unprecedented Iron‐Catalyzed Cross‐Coupling of Primary and Secondary Alkyl Grignard Reagents with Non‐activated Aryl Chlorides.

AbstractThe reactions of primary Grignards give the corresponding alkylated arenes in high yields, whereas secondary substrates provide a mixture of isomeric products in moderate yields.