Addition Of Grignard Reagents Research Articles

Distinguishing Organomagnesium Species in the Grignard Addition to Ketones with X-Ray Spectroscopy.

The addition of Grignard reagents to ketones is a well-established textbook reaction. However, a comprehensive understanding of its mechanism has only recently begun to emerge. X-ray spectroscopy, because of its high selectivity and sensitivity, is the ideal tool for distinguishing between an ensemble of competing pathways. With this aim in mind, we investigated the concerted mechanism of the addition of methylmagnesium chloride (CH3MgCl) to acetone in tetrahydrofuran by simulating the X-ray spectra of different molecules in solution. We used electronic structure methods to calculate the X-ray absorption spectra at the Mg K- and L1-edges and the X-ray photoelectron spectra at the Mg K-edge for different organomagnesium species, which coexist in solution due to the Schlenk equilibrium. The simulated spectra show that individual species can be distinguished throughout the different stages of the reaction. Each species has a distinct spectral feature which can be used as a fingerprint in solution. The absorption and photoelectron spectra consistently show a blue shift as the reaction progressed from reagents to products.

Grignard Reagent Addition to Pyridinium Salts: A Catalytic Approach to Chiral 1,4-Dihydropyridines.

Catalytic dearomatization of pyridinium salts is a powerful technique for constructing chiral N-heterocycles, which are crucial in alkaloid natural products and drugs. Despite its potential, progress in metal-catalyzed asymmetric dearomatization of pyridinium derivatives has been limited. Here, we present the enantioselective 1,4-dearomatization of pyridinium salts using Grignard reagents and chiral copper catalysis. This approach yields enantioenriched functionalized 1,4-dihydropyridines. Experimental kinetic isotope effects and density functional theory calculations provide insights into the reaction mechanism, regio- and enantioselectivity, and the rate-limiting step.

Regio‐ and Diastereoselective Conjugate Addition of Grignard Reagents to Chiral Fluoroalkyl α,β‐Unsaturated N‐tert‐Butanesulfinyl Ketimines: Synthesis of Optically Active Fluorinated Enamines and Derivatives

AbstractA regio‐ and diastereoselective conjugate addition reaction of Grignard reagents to fluoroalkyl α,β‐unsaturated N‐tert‐butanesulfinyl ketimines was disclosed. A range of different fluoroalkyls and Grignard reagents were well tolerated, giving up to 99% diastereomeric and regioisomeric ratios. This reaction provided a straightforward method for the synthesis of a variety of enantiomerically enriched α‐fluorinated enamines and derivatives which are difficult to achieve with other methods.

Insight into Radical Initiation, Solvent Effects, and Biphenyl Production in Iron-Bisphosphine Cross-Couplings.

Iron-bisphosphines have attracted broad interest as highly effective and versatile catalytic systems for two- and three-component cross-coupling strategies. While recent mechanistic studies have defined the role of organoiron(II)-bisphosphine species as key intermediates for selective cross-coupled product formation in these systems, mechanistic features that are essential for catalytic performance remain undefined. Specifically, key questions include the following: what is the generality of iron(II) intermediates for radical initiation in cross-couplings? What factors control reactivity toward homocoupled biaryl side-products in these systems? Finally, what are the solvent effects in these reactions that enable high catalytic performance? Herein, we address these key questions by examining the mechanism of enantioselective coupling between α-chloro- and α-bromoalkanoates and aryl Grignard reagents catalyzed by chiral bisphosphine-iron complexes. By employing freeze-trapped 57Fe Mössbauer and EPR studies combined with inorganic synthesis, X-ray crystallography, reactivity studies, and quantum mechanical calculations, we define the key in situ iron speciation as well as their catalytic roles. In contrast to iron-SciOPP aryl-alkyl couplings, where monophenylated species were found to be the predominant reactive intermediate or prior proposals of reduced iron species to initiate catalysis, the enantioselective system utilizes an iron(II)-(R,R)-BenzP* bisphenylated intermediate to initiate the catalytic cycle. A profound consequence of this radical initiation process is that halogen abstraction and subsequent reductive elimination result in considerable amounts of biphenyl side products, limiting the efficiency of this method. Overall, this study offers key insights into the broader role of iron(II)-bisphosphine species for radical initiation, factors contributing to biphenyl side product generation, and protocol effects (solvent, Grignard reagent addition rate) that are critical to minimizing biphenyl generation to obtain more selective cross-coupling methods.

W-Phos Ligand Enables Copper-Catalyzed Enantioselective Alkylation of N-Sulfonyl Ketimines with Grignard Reagents

Catalytic asymmetric addition of reactive Grignard reagents to ketimines poses a considerable challenge. Herein, a PNP-type W-Phos ligand developed recently by our group showed a unique effect toward this end, paving the way to a Cu(I)-catalyzed asymmetric alkylation reaction of N-sulfonyl ketimines, delivering optically active α-tertiary amines in high enantioselectivities. This catalytic protocol shows an unprecedented substrate scope with more than 80 examples, not only compatible with benzo five- and six-membered cyclic N-sulfonyl ketimines but also suitable for geometrically unstable (E or Z) acyclic N-sulfonyl ketimines. The application potential of the protocol is featured by the extensive presence of α-tertiary amines in natural products and pharmaceutical compounds and also demonstrated by downstream transformations with maintenance of the enantioselectivity.

Total synthesis of C37 alken-2-one temperature geomarkers

The total synthesis of the natural (8E,15E,22E)-heptatriaconta-8,15,22-trien-2-one and (15E,22E)-heptatriaconta-15,22-dien-2-one is reported. Our synthesis involved a modular and convergent approach, based on the copper-catalyzed addition of Grignard reagents to allylic olefins. The obtention of these methyl ketones is an important asset for the use of these compounds as analytical patterns with application in Earth sciences.

Structural Features of Diacyldodecaheterocycles with Pseudo-C2-Symmetry: Promising Stereoinductors for Divergent Synthesis of Chiral Alcohols.

Pseudo-C2-symmetric dodecaheterocyclic structures, which possess two acyl/aroyl groups disposed on either a cis- or trans-relative configuration, were prepared from the naturally occurring (-)-(1R)-myrtenal. Addition of Grignard reagents (RMgX) to the diastereoisomeric mixture of these compounds unexpectedly showed that nucleophilic additions to the two prochiral carbonyl centers gave the same stereochemical result in both cis/trans diastereoisomers, making unnecessary the separation of this mixture. Noticeably, both carbonyl groups showed different reactivity because one of them is attached to an acetalic carbon and the other to a thioacetalic carbon. Furthermore, addition of RMgX to the carbonyl attached to the former carbon takes place through the re face, while addition to the second one proceeds through the si face, thus affording the corresponding carbinols in a highly diastereoselective process. This structural feature allowed the sequential hydrolysis of both carbinols, yielding separately (R)- and (S)-1,2-diols after reduction with NaBH4. The mechanism of the asymmetric Grignard addition was explained by density functional theory calculations. This approach contributes to the development of the divergent synthesis of structurally and/or configurationally different chiral molecules.

Progress on the Cu-Catalyzed 1,4-Conjugate Addition to Thiochromones.

Carbon-carbon bond formation is one of the most important tools in synthetic organic chemists' toolbox. It is a fundamental transformation that allows synthetic chemists to synthesize the carbon framework of complex molecules from inexpensive simple starting materials. Among the many synthetic methodologies developed for the construction of carbon-carbon bonds, organocopper reagents are one of the most reliable organometallic reagents for this purpose. The versatility of organocuprate reagents or the reactions catalyzed by organocopper reagents were demonstrated by their applications in a variety of synthetic transformations including the 1,4-conjugate addition reactions. Sulfur-containing heterocyclic compounds are a much less studied area compared to oxygen-containing heterocycles but have gained more and more attention in recent years due to their rich biological activities and widespread applications in pharmaceuticals, agrochemicals, and material science. This paper will provide a brief review on recent progress on the synthesis of an important class of sulfur-heterocycles-2-alkylthiochroman-4-ones and thioflavanones via the conjugate additions of Grignard reagents to thiochromones catalyzed by copper catalysts. Recent progress on the synthesis of 2-substituted thiochroman-4-ones via alkynylation and alkenylation of thiochromones will also be covered in this review.

Investigation of a novel approach to the core of stemofoline: enantioselective construction of a bicyclic intermediate with three contiguous chiral centers

<p indent="0mm">The enantioselective synthesis of a bicyclic intermediate containing three contiguous chiral centers for a novel approach to the core of stemofoline is described. A (<italic>S</italic>)-malimide derivative developed in this laboratory was used as the chiral building block. The latter was converted in three steps (<italic>N</italic>-deprotection, a Mitsunobu reaction, and a cross-olefin metathesis) into another malimide with the <italic>N</italic>-substituent bearing a nucleophilic allylic silane moiety. The Grignard reagent addition took place regioselectively at the C-2 carbonyl to yield a hemiaminal. The key intramolecular aza-Sakurai reaction was promoted by trifluoroboron etherate, which led to the desired cyclization in good to excellent combined yields. Four diastereomers were formed from this reaction, whose stereochemistries were determined by NOESY technique. The latter revealed that the major diastereomer (obtained in 35% yield) possessed the correct stereochemistries required for the total synthesis of natural enantiomer of stemofoline. A regioselective Wacker oxidation resulted in the formation of the title compound along with a minor regioisomer (an aldehyde) in a ratio of 18: 1 (combined yield: 50%).

Nucleophilic Addition of 4,5-Dihydrooxazole Derivatives to Base Generated o-Quinone Methides: A Four-Component Reaction.

A novel method for joining four components together in a single pot leading to an assortment of N-amino-benzylated phenols is described. The method involves the addition of different Grignard reagents to various o-OBoc salicylaldehydes in the presence of assorted 4,5-dihydrooxazoles, followed by aqueous workup. Seventeen examples are presented with varied (-R, -R' -R″, -R‴, -R⁗, and Cn) substituents.

Synthesis of 1,4-ketoaldehydes and 1,4-diketones by Mo-catalyzed oxidative cleavage of cyclobutane-1,2-diols.

A new two-step procedure for the synthesis of 1,4-dicarbonyls has been developed involving an efficient and clean Mo-catalyzed oxidative cleavage of cyclobutane-1,2-diols with DMSO, which is used as solvent and oxidant. The required starting glycols were prepared by nucleophilic additions of organolithiums and Grignard reagents to easily available 2-hydroxycyclobutanones.

Tandem addition of nucleophilic and electrophilic reagents to vinyl phosphinates: the stereoselective formation of organophosphorus compounds with congested tertiary carbons.

Carbon anions formed via the addition of Grignard reagents to SP-vinyl phosphinates were modified with electrophilic reagents to afford organophosphorus compounds with diverse carbon skeletons. The electrophiles included acids, aldehydes, epoxy groups, chalcogens and alkyl halides. When alkyl halides were used, bis-alkylated products were afforded. Substitution reactions or polymerization occurred when the reaction was applied to vinyl phosphine oxides.

Asymmetric synthesis of the sex pheromone of the apple leafminer, Lyonetia prunifoliella.

Lyonetia prunifoliella is a significant pest in orchards and damages apple. The sex pheromones of this pest were prepared via a new and concise method. The central to our method were Evans' chiral auxiliaries, the addition of chiral Grignard reagent to aldehyde and Wittig coupling.

Total Synthesis of Patulone: A Natural Xanthonoid Possessing a Geminally Diisoprenylated Structure

AbstractThe first total synthesis of patulone, a plant metabolite possessing a unique 1,1-diisoprenyl-1H-xanthene-2,9-dione structure, is described. Starting from a 1-fluroxanthone derivative with suitable substitution pattern, the pivotal gem-diisoprenylation was efficiently accomplished by implementing twice the sequence of addition of isoprenyl Grignard reagent to the carbonyl at C9 and anion-accelerated oxy-Cope rearrangement.

Catalytic Access to 4-(sec-Alkyl)Anilines via 1,6-Conjugate Addition of Grignard Reagents to in Situ Generated aza-p-Quinone Methides.

The synthesis of aniline derivatives, common building blocks in many pharmaceuticals, agrochemicals, dyes or polymers, has been limited to reactions based on benzene-toluene-xylene derivatives (BTX) due to their ample availability. Despite the large number of existing methodologies, the synthesis of chiral 4-(sec-alkyl)anilines has not been accomplished so far. In this work, a tandem strategy based on the generation of a reactive aza-p-quinone methide (aza-p-QM) intermediate followed by Cu(I)-catalyzed addition of Grignard reagents has been developed.

Synthesis of W‐Phos Ligand and Its Application in the Copper‐Catalyzed Enantioselective Addition of Linear Grignard Reagents to Ketones

AbstractThe asymmetric catalytic addition of linear Grignard reagents to ketones has been a long‐standing challenge in organic synthesis. Herein, a novel family of PNP ligands (W‐Phos) was designed and applied in copper‐catalyzed asymmetric addition of linear Grignard reagents to aryl alkyl ketones, allowing facile access to versatile chiral tertiary alcohols in good to high yields with excellent enantioselectivities (up to 94 % yield, 96 % ee). The process can also be used to synthesize chiral allylic tertiary alcohols from more challenging α,β‐unsaturated ketones. Notably, the potential utility of this method is demonstrated in the gram‐scale synthesis and modification of various densely functionalized medicinally relevant molecules.

Synthesis of W-Phos Ligand and Its Application in the Copper-Catalyzed Enantioselective Addition of Linear Grignard Reagents to Ketones.

The asymmetric catalytic addition of linear Grignard reagents to ketones has been a long-standing challenge in organic synthesis. Herein, a novel family of PNP ligands (W-Phos) was designed and applied in copper-catalyzed asymmetric addition of linear Grignard reagents to aryl alkyl ketones, allowing facile access to versatile chiral tertiary alcohols in good to high yields with excellent enantioselectivities (up to 94 % yield, 96 % ee). The process can also be used to synthesize chiral allylic tertiary alcohols from more challenging α,β-unsaturated ketones. Notably, the potential utility of this method is demonstrated in the gram-scale synthesis and modification of various densely functionalized medicinally relevant molecules.

A Nonoxidative Sequence for the Preparation of 1,2-Diketone Derivatives Using Aldehyde and Organometallic Building Blocks

This study investigates a synthetic sequence for the preparation of 1,2-diketone products. The sequence avoids oxidative conditions and instead employs reliable transformations including the Horner-Wadsworth-Emmons and addition of Grignard reagents to N-methyl-N-methoxy (Weinreb) amide intermediates. The reaction sequence is suitable for the synthesis of nonsymmetric aliphatic and aryl substituted derivatives.

Stereoselective Synthesis and Anticancer Activity of 2,6-Disubstituted trans-3-Methylidenetetrahydropyran-4-ones.

In this report, we present efficient and stereoselective syntheses of 2,6-disubstituted trans-3-methylidenetetrahydropyran-4-ones and 2-(4-methoxyphenyl)-5-methylidenetetrahydropyran-4-one that significantly broaden the spectrum of the available methylidenetetrahydropyran-4-ones with various substitution patterns. Target compounds were obtained using Horner–Wadsworth–Emmons methodology for the introduction of methylidene group onto the pyranone ring. 3-Diethoxyphosphoryltetrahydropyran-4-ones, which were key intermediates in this synthesis, were prepared by fully or highly stereoselective addition of Gilman or Grignard reagents to 3-diethoxyphosphoryldihydropyran-4-ones. Addition occurred preferentially by axial attack of the Michael donors on the dihydropyranone ring. Relative configurations and conformations of the obtained adducts were assigned using a detailed analysis of the NMR spectra. The obtained methylidenepyran-4-ones were evaluated for cytotoxic activity against two cancer cell lines (HL-60 and MCF-7). 2,6-Disubstituted 3-methylidenetetrahydropyran-4-ones with isopropyl and phenyl substituents in position 2 were more cytotoxic than analogs with n-butyl substituent. Two of the most cytotoxic analogs were then selected for further investigation on the HL-60 cell line. Both analogs induced morphological changes characteristic of apoptosis in cancer cells, significantly inhibited proliferation and induced apoptotic cell death. Both compounds also generated DNA damage, and one of the analogs arrested the cell cycle of HL-60 cells in the G2/M phase. In addition, both analogs were able to inhibit the activity of topoisomerase IIα. Based on these findings, the investigated analogs may be further optimized for the development of new and effective topoisomerase II inhibitors.

Synthesis of Triazabenzo[a]pyrenes and Their Photophysical, Acid‐Responsive, and Electrochemical Properties

AbstractA series of triazabenzo[a]pyrenes comprising a cata‐condensed pyridine ring and 4,10‐diazapyrene framework were synthesized from commercially available materials in the following three steps: palladium‐catalyzed direct C−H arylation, nucleophilic addition of Grignard reagents to cyano groups, and copper‐catalyzed oxidative C−N bond formation. The triazabenzo[a]pyrenes showed superior electron‐accepting properties and narrower HOMO‐LUMO energy gaps compared to the corresponding 4,10‐diazapyrene derivative because of the condensation of an electron‐deficient pyridine ring. The photophysical, acid‐responsive, and electrochemical properties of triazabenzo[a]pyrenes depend on the position of the nitrogen atom in the cata‐condensed pyridine ring. Density functional theory calculations revel that the condensation of a pyridine ring leads to a lowering of the LUMO energy level thereby enhancing the electron‐accepting properties.