Magnesium Bis Amide Research Articles

Reactivity of the magnesium bisamide complex towards C=C=O-, N=C=O-, and N—N=O-containing substrates

Reactivity of the magnesium bisamide complex towards C=C=O-, N=C=O-, and N—N=O-containing substrates

N‐Ligand‐Enabled Aromatic Nucleophilic Amination of 1,2‐Diaryl‐o‐Carboranes with (R2N)2Mg for Selective Synthesis of 4‐R2N‐o‐Carboranes and 2‐R2N‐m‐Carboranes

AbstractThe nucleophilic aromatic BH substitution reaction of carboranes is uncommon, compared to the electrophilic one. This work reported a pyridine‐enabled transition‐metal‐free regioselective nucleophilic aromatic cage B(4)‐H amination of 1,2‐diaryl‐o‐carboranes with magnesium bisamides, giving a series of B(4)‐aminated o‐carboranes. DFT calculations showcased a stepwise B−N formation/B−H cleavage process, in which Mg−H formation/cage closure is the rate‐determining step. Unprecedentedly, in the presence of 4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl (dtbpy), a tandem B(4)‐amination/cage isomerization reaction of o‐carboranes was discovered for the facile preparation of B(2)‐aminated m‐carboranes. Control experiments indicated that magnesium complex, bidentate ligand (dtbpy) and reaction temperature were crucial in the cage isomerization process. This direct nucleophilic aromatic cage B−H amination reaction offers an alternative strategy for selective amination of o‐ and m‐carboranes.

N-Ligand-Enabled Aromatic Nucleophilic Amination of 1,2-Diaryl-o-Carboranes with (R2 N)2 Mg for Selective Synthesis of 4-R2 N-o-Carboranes and 2-R2 N-m-Carboranes.

The nucleophilic aromatic BH substitution reaction of carboranes is uncommon, compared to the electrophilic one. This work reported a pyridine-enabled transition-metal-free regioselective nucleophilic aromatic cage B(4)-H amination of 1,2-diaryl-o-carboranes with magnesium bisamides, giving a series of B(4)-aminated o-carboranes. DFT calculations showcased a stepwise B-N formation/B-H cleavage process, in which Mg-H formation/cage closure is the rate-determining step. Unprecedentedly, in the presence of 4,4'-di-tert-butyl-2,2'-dipyridyl (dtbpy), a tandem B(4)-amination/cage isomerization reaction of o-carboranes was discovered for the facile preparation of B(2)-aminated m-carboranes. Control experiments indicated that magnesium complex, bidentate ligand (dtbpy) and reaction temperature were crucial in the cage isomerization process. This direct nucleophilic aromatic cage B-H amination reaction offers an alternative strategy for selective amination of o- and m-carboranes.

Generation of cycloalkynes through deprotonation of cyclic enol triflates with magnesium bisamides

Deprotonative generation of cyclohexynes, cycloheptynes, and cyclooctynes was achieved by controlling the reactivities of transient anionic species from the corresponding enol triflates with magnesium bis(2,2,6,6-tetramethylpiperidide) as a base. The starting enol triflates are readily obtained through triflation of the corresponding ketones, allowing direct access to the cycloalkynes.

ChemInform Abstract: Towards Energetically Viable Asymmetric Deprotonations: Selectivity at more Elevated Temperatures with C2‐Symmetric Magnesium Bisamides.

AbstractThe novel C2‐symmetric magnesium bisamide MBSA shows an unique ability to function efficiently in asymmetric deprotonation reactions.

Towards energetically viable asymmetric deprotonations: selectivity at more elevated temperatures with C2-symmetric magnesium bisamides

A novel chiral magnesium bisamide has enabled the development of effective asymmetric deprotonation protocols at substantially more elevated temperatures. This new, structurally simple, C(2)-symmetric magnesium complex displays excellent levels of asymmetric efficiency and energy reduction in the synthesis of enantioenriched enol silanes.

New Potentially Chelating Chiral Magnesium Amide Bases for Use in Enantioselective Deprotonation Reactions

A series of chiral secondary amines, incorporating a 5- or 6-membered heterocycle, were synthesised and used to prepare novel chiral magnesium bisamide reagents. These amide bases were subsequently applied within asymmetric deprotonation reactions to probe the potential for chelation-assisted selectivity enhancement. Good levels of selectivity could be achieved (up to 87:13 e.r. (R:S)) across a range of prochiral cyclohexanone substrates when employing a thiophene-derived magnesium bisamide complex.

ChemInform Abstract: Enantioselective Deprotonation Reactions Using a Novel Homochiral Magnesium Amide Base.

A novel homochiral magnesium bisamide base system has been prepared and reacted with a series of prochiral ketones in the presence of TMSCl to give efficient formation of the corresponding enol ethers in enantiomeric ratios of up to 95∶5.

On the Mechanism of CO2 Insertion into the Mg‐N Bond of Molecular Mono‐ and Dinuclear Magnesium Compounds: A Quantum Chemical Study

AbstractHerein the mechanism for CO2 fixation by alkylmagnesium amides and magnesium bisamides is analyzed on the basis of DFT (density functional theory) calculations relying on the functionals BP86 and B3LYP in combination with a TZVPP basis set. Monomeric as well as dimeric compounds were considered, and prior to the CO2 reactions the thermodynamics of several equilibria (monomer‐dimer, disproportionation) is analyzed. Additional calculations were performed to study the mechanism for CO2 fixation in the presence of a chelating donor molecule, namely ethylene diamine, which preferentially complexes the monomeric alkylmagnesium amide. On the basis of the calculations it is suggested that (i) for monomeric magnesium compounds CO2 insertion into the Mg‐N bonds proceeds without a barrier to an intermediate featuring a four‐membered MgOCN ring and then with a relatively small barrier to the carbamate, (ii) for dinuclear magnesium compounds CO2 insertion is opposed by a significant barrier, and (iii) the addition of donor ligands which coordinate to the monomeric species shifts the monomer‐dimer equilibrium to the monomer side, and in addition leads to direct carbamate formation without any intermediate stage and with no reaction barrier. The studies might be of interest for a better understanding of enzymatic reactivity.

Novel Enantiomerically Pure Heteroleptic Magnesium Complexes for Use in Enantioselective Deprotonation Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel Enantiomerically PureHeteroleptic Magnesium Complexes for Use in Enantioselective DeprotonationReactions

Two classes of heteroleptic magnesium complexes, alkyl­magnesium amides RMgNR2 and aryloxymagnesium amides ROMgNR2, have been prepared and subsequently shown to be efficient bases in the enantioselective deprotonation of substituted cyclic ketones. When compared with their magnesium bisamide counterparts, significantly different reactivity and selectivity profiles, including an unexpected reversal in enantioselectivity, has been observed with the new reagents.

Magnesium Amide Base‐Mediated Enantioselective Deprotonation Processes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

New insights in the search for chiral Brønsted bases.

The concept of using chiral bases in asymmetric synthesis appeared with the emergence of the chemistry of chiral lithium amides. In recent years, new classes of chiral bases, such as chiral magnesium bisamides and chiral alkali alkoxides have proven to be highly efficient and easy to handle. This paper highlights recent advances and new concepts in the chemistry of this second generation of chiral bases.

Magnesium amide base-mediated enantioselective deprotonation processes

A novel homochiral magnesium bisamide has been readily prepared and, following careful optimisation, this species has been shown to react efficiently with a series of prochiral 4-substituted cyclohexanones in the presence of TMSCl to give the corresponding silyl enol ethers in enantiomeric ratios of up to 95:5. Additionally, the same chiral base system has been shown to be highly effective in the desymmetrisation of cis-2,6-disubstituted cyclohexanones, providing excellent levels of both conversion and enantioselection (up to >99.5:0.5 er). Furthermore, the magnesium bisamide has also been shown to mediate a kinetic resolution process with the corresponding trans-disubstituted substrates, allowing access to enantioenriched enol ethers and ketones.

ChemInform Abstract: Magnesium Bisamides as Reagents in Synthesis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Magnesium bisamides as reagents in synthesis.

As part of the continued requirement for more selective reagents in organic synthesis, magnesium bisamides are becoming established as a class of organometallic bases with considerable potential. Their relatively mild reactivity, combined with their high degree of steric congestion, leads to a distinct class of reagents with significantly different chemo-, regio-, stereo- and enantioselectivities when compared with existing species and protocols.

Enantioselective deprotonation reactions using a novel homochiral magnesium amide base

A novel homochiral magnesium bisamide base system has been prepared and reacted with a series of prochiral ketones in the presence of TMSCl to give efficient formation of the corresponding enol ethers in enantiomeric ratios of up to 95∶5.