Simple Grignard Reagents Research Articles

A Nonconventional Approach toward Multihydroxy Functional Polystyrenes Relying on a Simple Grignard Reagent

Capitalizing on the inertness of styrene toward Grignard reagents, 4-vinylphenylmagnesium bromide was utilized for the rapid and convenient preparation of the protected monomer 2,2-dimethyl-4-(4-vinylbenzyl)-1,3-dioxolane (DMVBDO), avoiding the use of catalysts and painstaking purification protocols. Well-defined homopolymers, statistical copolymers, and block copolymers with styrene (S) as a comonomer were prepared in THF at −78 °C via carbanionic living polymerization. The overall molecular weights ranged from 4.5 to 68.9 kg mol–1 with low dispersities (Đ 1.04–1.15). Copolymers were synthesized with styrene feed ratios (Xfeed) from 15 to 95 mol % with glass transition temperatures (Tg) between 46 and 91 °C. Whereas polystyryllithium served as an excellent macroinitiator for the preparation of the block copolymer PS0.5-b-P(DMVBDO)0.5, the inverse block order, i.e., synthesis of P(DMVBDO)0.5-b-PS0.5, yielded a bimodal molecular weight distribution (MWD) with increased dispersity, which is ascribed to slow crossover. Rapid deprotection of both homo- and copolymers to release two hydroxyl groups per DMVBDO unit was achieved via acidic hydrolysis. The deprotected block copolymer PS0.5-b-P(VPPDO)0.5 showed phase separation, indicated by two Tg values (68 and 86 °C). Homogeneous brush copolymers of the type P(S85-co-VPPDO5)-g-PLLA and P(S85-co-VPPDO6)-g-PEO were demonstrated by using quantitative “grafting from” with l-lactide and ethylene oxide, respectively. The brush-like copolymers were obtained in quantitative yields while maintaining monodisperse MWD.

Highly diastereoselective preparation of chiral NHC-boranes stereogenic at the boron atom.

Stereogenic main group elements are clearly generating interest in the enantioselective catalysis field. Surprisingly, while chiral organoboron reagents are very useful in stereoselective transformations, few scaffolds stereogenic at boron and configurationally stable have been reported to date. Herein, we describe an original library of chiral NHC-boranes, stereogenic at the boron atom, that has been prepared in only a few steps and in good yields (up to 93%). Key steps involve a chlorination/arylation sequence in the presence of simple Grignard reagents from bicyclic NHC-boranes. The high and unprecedented diastereoselectivity observed during the second step (up to 99 : 1 dr) has been rationalized through a plausible SRN1 mechanism thanks to EPR observations and DFT calculations.

Elucidating the Requirements for Reversible Magnesium Electrodeposition and Dissolution

We compare the electrochemistry of Mg deposition and stripping from three Mg-battery electrolytes: EtMgBr, Mg(AlCl2EtBu)2, and MgCl2-AlCl3. These electrolytes represent three generations of progress in Mg-battery development, and include a simple Grignard reagent, an organohaloaluminate, and an all inorganic system, respectively. Our electrochemical measurements coupled with surface and bulk analytical techniques elucidate the requirements for reversible Mg deposition and definitively establish that voltammetric cycling of the electrolyte significantly alters their composition and performance. In the cases of EtMgBr and Mg(AlCl2EtBu)2, electrochemical quartz crystal microbalance measurements demonstrate that mass is gained and lost from the electrode with relatively high efficiency. However, the charge passed during stripping is consistently less than that passed during deposition, resulting in chronoamperometric charge efficiencies between 80-100% for EtMgBr and 50-70% for Mg(AlCl2EtBu)2. SEM-EDS analysis of electrode surfaces demonstrates irreversible Mg deposition and stripping. GC-MS and NMR analysis of electrolytes reveal decomposition of the solvent-electrolyte system. For the all inorganic system containing MgCl2-AlCl3 in THF, elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM-EDS) results demonstrate that irreversible Mg and Al deposits form during early cycles. Electrospray ionization-mass spectrometry (ESI-MS) data show that inhibitory oligomers develop in THF-based solutions. These oligomers form via the well-established mechanism of a cationic ring-opening polymerization of THF during the initial synthesis of the MgCl2-AlCl3 electrolyte and under resting conditions. In contrast, solutions containing MgCl2-AlCl3 in 1,2-dimethoxyethane (DME), an acyclic solvent, do not evolve as dramatically at open circuit potential. From these results, we propose a mechanism describing how the conditioning process of MgCl2-AlCl3 in THF improves its performance by both tuning the Mg:Al stoichiometry and eliminating oligomers. We also explore the role that other solvents and metal chlorides play in the properties of inorganic Mg-battery electrolytes.

Investigating the Reversibility of in Situ Generated Magnesium Organohaloaluminates for Magnesium Deposition and Dissolution

We compare the electrochemistry of Mg deposition and stripping from Mg(AlCl2EtBu)2 in THF, a common electrolyte used in Mg-ion battery prototypes, with EtMgBr, a simple Grignard reagent. Electrochemical quartz crystal microbalance measurements demonstrate that mass is gained and lost from the electrode with relatively high efficiency. However, the corresponding Coulombic efficiency is considerably less than the expected 100% for early stage cycles. SEM-EDS analysis shows accumulation of Mg and electrolyte constituents after stripping, highlighting the irreversibility of the Mg deposition and stripping process. GC-MS and NMR analysis of electrolytes reveal decomposition of the solvent–electrolyte system. These findings suggest that Mg organohaloaluminates are not ideal for use in robust Mg-ion batteries.

ChemInform Abstract: Iron‐Catalyzed Cross‐Coupling Between 1‐Bromoalkynes and Grignard‐Derived Organocuprate Reagents.

AbstractThe use of in situ generated organocopper instead of simple Grignard reagents is the key factor to suppress undesirable side homocoupling and to lead the reaction to completion.

Copper‐Catalyzed Asymmetric Ring Opening of Oxabicyclic Alkenes with Grignard Reagents.

Simple Grignard reagents were applied in copper-catalyzed asymmetric ring-opening reactions of oxabenzonorbornadiene derivatives using spiro phosphoramidite ligands. Excellent anti-stereoselectivities and good enantioselectivities were achieved.

Copper-Catalyzed Asymmetric Ring Opening of Oxabicyclic Alkenes with Grignard Reagents

[reaction: see text] Simple Grignard reagents were applied in copper-catalyzed asymmetric ring-opening reactions of oxabenzonorbornadiene derivatives using spiro phosphoramidite ligands. Excellent anti-stereoselectivities and good enantioselectivities were achieved.

Process Research on [(2S)-(3-Fluorophenyl)-(1S)-(5-oxotetrahydrofuran- 2-yl)ethyl]carbamic Acid tert-Butyl Ester, a Lactone Intermediate for an Aspartyl Protease Inhibitor

Two processes for the preparation of lactone [2S-(3-fluorophenyl)-1S-(5-oxotetrahydrofuran-2-yl)ethyl]carbamic acid tert-butyl ester 1 starting from S-BOC-(3-fluorophenyl)alanine 3 are described. (S)-(3-Fluorophenyl)alanine N-methyl-N-methoxy amide 10, the Weinreb amide of 3, was reacted with 2-(2-1,3-dioxanyl)ethylmagnesium bromide to provide key intermediate ketoacetal 11. To achieve high yields for this conversion, the N−H of the BOC group in Weinreb amino acid amide 10 was deprotonated first with a simple Grignard reagent (methyl or benzylmagnesium halide) followed by Barbier reaction with magnesium metal and 2-(2-bromoethyl)-1,3-dioxane. The acetal group in 11 was opened oxidatively with ozone, and the resulting ester 15 was reduced selectively at low temperature with N-Selectride. Alternatively, the ketone moiety in 11 was reduced diastereoselectively with aluminum triisopropoxide in 2-propanol to give the undesired (R,S)-diastereomeric alcohol. The alcohol was converted to the mesylate which was heated in solution to cause formation of oxazolidinone 19 through displacement of the mesylate group by the carbonyl moiety of the BOC group with loss of tert-butyl alcohol. This intramolecular reaction provided the desired (S,S)-diastereomer. Finally, acetal 19 was converted to nitrile 20 with hydroxylamine hydrochloride in ethanol with catalytic toluenesulfonic acid at reflux. Basic aqueous hydrolysis of nitrile 20 followed by treatment with di-tert-butyl dicarbonate provided 1. While the second process was longer, the inexpensive reagents, simple reaction conditions, and high yields made it the process of choice. Both processes have been run on a multikilogram scale.

New practical tungsten(VI) based catalyst systems for ring opening metathesis polymerisation

Tungsten(VI) complexes of the type trans-[WCl 2(diol)(OAr) 2] were studied as catalyst precursors for ROMP of norbornene and dicyclopentadiene. These compounds form active catalysts when treated by simple Grignard reagents, such as methyl magnesium iodide or neophyl magnesium chloride. Moreover, polymerisations can be run under ambient atmosphere without complicated inert atmosphere techniques.

Michael addition of Grignard reagents to tetraethyl ethenylidenebisphosphonate

Tetraethyl ethenylidenebisphosphonate can undergo facile Michael type addition reaction with simple Grignard reagents to give alkyl, arylalkyl, aryl C-substituted methylene bisphosphonates. This addition easily occurs even if funtionalised Grignard reagents are used.

Reactions of (Triphenylsilyl)ethylene Oxide with Grignard Reagents (and with MgBr(2)). A Reinvestigation.

Reactions of (triphenylsilyl)ethylene oxide (1) with simple Grignard reagents such as EtMgBr and PhMgBr have been reported to yield crystalline hydroxysilanes assigned as the alpha-hydroxy silanes expected from beta opening of the epoxide. Reinvestigation of these reactions showed that the hydroxysilanes were the beta-hydroxy silanes 4 and 7 expected from a rearrangement-trapping sequence; a bromohydrin, assigned as the alpha-bromo-beta-hydroxy silane 9 from alpha opening, and (triphenylsilyl)acetaldehyde (8) were also formed.

Diastereoselective reactions of grignard reagents with chiral amino lactols derived firom L-aspartic acid

Nucleophilic additions to chiral amino lactols obtained from L-aspartic acid containing a chiral α-silyloxymethyl function by simple Grignard reagents exhibited high stereoselectivity to provide the corresponding optically active amino alcohols containing three contiguous stereogenic centers. The mechanistic origin of the asymmetric induction is rationalized based on chelation controlled models.

Preparation of some NCA [1- 11C]acid chlorides as labelling agents

The [ 11C]carbonation of simple Grignard reagents (RMgX, R = Et, Pr, cyclo-Bu; X = Br) with cyclotron-produced [ 11C]carbon dioxide followed by direct treatment of the 11C adducts with phthaloyl dichloride and 2,6-di-t-butylpyridine affords [1- 11C]acid chlorides in useful radiochemical yields (> 10–30%, decay-corrected from 11CO 2), as assessed by HPLC and TLC of the labelled amides formed by reaction with 1,2,3,4-tetrahydroisoquinoline. With suitable precuations these [1- 11C]acid chlorides can be isolated at high specific activity within 15 min from radionuclide production as labelling agents for potential radiopharmaceuticals for PET. The preparation of [1- 11C]benzoyl chloride without isolation has also been demonstrated.