Addition Of Organolithiums Research Articles

Merging Organolithium Chemistry and Stereoselective Biocatalysis: Transformation of Aromatic Nitriles into Chiral Alcohols

AbstractThe combination of RLi‐mediated organic transformations (under air and at room temperature) with a subsequent stereoselective biocatalytic reaction is for the first time presented. Most of the previous asymmetric chemoenzymatic routes have been limited to the concomitant or sequential combination of transition metals/organocatalysts with enzymes. However, the use of polar organometallic reagents (RLi) in the design of these stereoselective hybrid protocols has been totally neglected, as far as we are concerned. Thus, in this work, the combination of organolithium chemistry and asymmetric biocatalysis is described for the first time in a one‐pot fashion. The chemoenzymatic approach converts a series of nitriles into chiral alcohols consisting of two steps, where the key item was the finding of suitable conditions to adapt the reactivities of organolithiums and alcohol dehydrogenases (ADHs) in the same recipient. The organolithium addition occurred with total chemoselectivity (no side reactions were observed) under neat conditions and room temperature leading to the corresponding imines, which were hydrolyzed using a buffer, and adjusting the pH for the subsequent ADH action. Commercial and made in house overexpressed ADHs allowed to produce chiral alcohols with excellent selectivities and good overall yields. The different behavior displayed for the reductive enzymes in the presence of diethyl ether clearly influenced in the decision to let the organolithium solvent evaporate under open‐air conditions before developing the bioreduction step. Our results demonstrate the importance of the fine orchestration of the reaction conditions for the development of efficient hybrid chemoenzymatic cascades without the need of intermediate isolation/purification steps or compartmentalization of the different synthetic systems.

A three-minute gram-scale synthesis of amines via ultrafast “on-water” in continuo organolithium addition to imines

A three-minute gram-scale synthesis of amines via ultrafast “on-water” in continuo organolithium addition to imines

Synthesis and structural confirmation of selaginpulvilin X.

We report the first total synthesis of the natural product selaginpulvilin X, a selaginellaceae polyphenol class of compounds. Our synthetic strategy employs cross-coupling reactions and an organolithium addition to construct the carbon framework. Subsequently, the functional group modifications and deprotection yield the natural product. Spectral analysis confirms the proposed structure by comparing natural and synthetic samples.

Dearomative triple elementalization of quinolines driven by visible light

Organoboron and organosilicon compounds are used not only as synthetic building blocks but also as functional materials and pharmaceuticals, and compounds with multiple boryl and silyl groups are beginning to be used for these purposes. Especially in drug discovery, methodology providing easy stereoselective access to aliphatic nitrogen heterocycles bearing multiple boryl or silyl groups from readily available aromatic nitrogen heterocycles would be attractive. However, such transformations remain challenging, and available reactions have been mostly limited to dearomative hydroboration or hydrosilylation reactions. Here, we report the dearomative triple elementalization (carbo-sila-boration) of quinolines via the addition of organolithium followed by photo-boosted silaboration, affording the desired products with complete chemo-, regio-, and stereoselectivity. The reaction proceeds via the formation of silyl radicals instead of silyl anions. We also present preliminary studies to illustrate the potential of silaboration products as synthetic platforms.

Dynamic Phenomena and Complexation Effects in the α-Lithiation and Asymmetric Functionalization of Azetidines.

In this work it is demonstrated that enantiomerically enriched N-alkyl 2-oxazolinylazetidines undergo exclusive α-lithiation, and that the resulting lithiated intermediate is chemically stable but configurationally labile under the given experimental conditions that afford enantioenriched N-alkyl-2,2-disubstituted azetidines. Although this study reveals the configurational instability of the diastereomeric lithiated azetidines, it points out an interesting stereoconvergence of such lithiated intermediates towards the thermodynamically stable species, making the overall process highly stereoselective (er > 95:5, dr > 85:15) after trapping with electrophiles. This peculiar behavior has been rationalized by considering the dynamics at the azetidine nitrogen atom, the inversion at the C-Li center supported by in situ FT-IR experiments, and DFT calculations that suggested the presence of η3-coordinated species for diastereomeric lithiated azetidines. The described situation contrasted with the demonstrated stability of the smaller lithiated aziridine analogue. The capability of oxazolinylazetidines to undergo different reaction patterns with organolithium bases supports the model termed “dynamic control of reactivity” of relevance in organolithium chemistry. It has been demonstrated that only 2,2-substituted oxazolinylazetidines with suitable stereochemical requirements could undergo C=N addition of organolithiums in non-coordinating solvents, leading to useful precursors of chiral (er > 95:5) ketoazetidines.

Transfer hydroarylation of ketones using directing-group-free, unstrained alcohols

In this issue of <i>Chem</i>, Morandi and coworkers report an exciting reversible transfer hydroarylation between ketones and unstrained arylated alcohols. Through a Rh-catalyzed β-aryl elimination process, the aryl moiety "shuttles" from the alcohol to the ketone substrate, which provides a milder alternative to conventional Grignard and organolithium addition chemistry.

Enantioselective, Organocatalytic Strategy for the Oxazolomycin Core: Formal Synthesis of (+)-Neooxazolomycin.

A concise, organocatalytic, enantioselective route to the γ-lactam core of the oxazolomycins was developed. Key steps include a Lewis base-catalyzed, Michael proton transfer-lactamization organocascade, a one-pot N-methylation and diastereoselective α-alkylation, a diastereotopic group-selective reduction, a substrate-directed allylic hydroxylation, and a lanthanide-mediated organolithium addition to append the side chain. A formal synthesis of (+)-neooxazolomycin via interception of a Kende intermediate, accessed in 10 steps (previously 24 steps from α-d-glucose), enabled confirmation of the relative and absolute stereochemistry.

The role of CuI in the siloxane-mediated Pd-catalyzed cross-coupling reactions of aryl iodides with aryl lithium reagents

Experiments indicate that a catalytic amount of CuI plays an important role in the siloxane-mediated Pd-catalyzed cross-coupling reactions with the direct use of organolithium reagents. Addition of organolithium to the siloxane transfer agent generates an organosilicon intermediate. DFT calculations indicate that CuI initially accelerates the Si-Pd(II) transmetalation of the organosilicon intermediate by the formation of CuI2−. Subsequently, CuI2− works as a shuttle between the Si-Cu(I) and Cu(I)-Pd(II) transmetalation processes.

Stereo- and Enantioselective Addition of Organolithiums to 2-Oxazolinylazetidines as a Synthetic Route to 2-Acylazetidines.

A new synthetic route to N-alkyl-2-acylazetidines was developed through a highly stereoselective addition of organolithiums to N-alkyl-2-oxazolinylazetidines followed by acidic hydrolysis of the resulting oxazolidine intermediates. This study revealed an unusual reactivity of the C=N bond of the oxazoline group when reacted with organolithiums in a non-polar solvent such as toluene. The observed reactivity has been explained considering the role of the nitrogen lone pair of the azetidine ring as well as of the oxazolinyl group in promoting a complexation of the organolithium, thus ending up with the addition to the C=N double bond. The high level of stereoselectivity in this addition is supported by DFT calculations and NMR investigations, and a model is proposed for the formation of the oxazolidine intermediates, that have been isolated and fully characterized. Upon acidic conditions, the oxazolidine moieties were readily converted into 2-acylazetidines. This synthetic approach has been applied for the preparation of highly enantioenriched 2-acylazetidines starting from chiral not racemic N-alkyl-2-oxazolinylazetidines.

Dichotomy within 1,4-addition of organolithium and Grignard reagents to α,β-unsaturated Fischer alkoxycarbenes: A new synthesis of Fischer carbenes

The reaction of organolithium and Grignard reagents with pentacarbonyl[(ethoxy)(2-phenylethenyl)carbene]chromium(0) gave, after the quenching of the initially formed product of the 1,4-addition, different products depending on the organometallic and quenching reagents used. The addition of organolithiums, followed by a work-up with acid (AcOH or HCl), afforded the corresponding carbene complexes. In contrast, quenching the reaction mixture with ethanol led to the stereoselective formation of (Z)-enol ethers. The usage of Grignard reagents led to the formation of the carbene complexes regardless of which quenching reagent was used.

Development of an Organometallic Flow Chemistry Reaction at Pilot-Plant Scale for the Manufacture of Verubecestat

We report the development of an organolithium addition to a chiral ketimine at pilot-plant scale using flow chemistry. Given the mixing sensitivity of this process, established previously at both lab and kilogram scale, we conducted critical experiments to understand the impact of flow rate, temperature, and mixing on the performance of the reaction in a factory-sized static mixer. Online process analytical technology was used to collect real-time data on batches to demonstrate steady-state operation over multiple hours and also to confirm the robustness of the continuous process against fouling. These experiments at pilot-plant scale provided improved operating parameters that enabled the implementation of this chemistry for the commercial manufacture of verubecestat, currently being evaluated in Phase III trials for the treatment of Alzheimer’s disease.

Enantiospecific Total Synthesis of (+)‐3‐epi‐Epohelmin A Using a Nitrogen‐Substituted Donor–Acceptor Cyclopropane

The enantiospecific total synthesis of (+)‐3‐epi‐epohelmin was accomplished by rapid construction of the pyrrolizidine core starting from enantiopure l‐pyroglutamic acid. The key reaction included a highly regio‐ and stereoselective intramolecular cyclopropanation reaction, regioselective ring opening of a nitrogen‐substituted donor–acceptor cyclopropane, stereoselective reduction of a ketone, chemoselective organolithium addition to a Weinreb amide, and chemoselective oxidation of an allylic alcohol.

Using Flow To Outpace Fast Proton Transfer in an Organometallic Reaction for the Manufacture of Verubecestat (MK-8931)

We report that an organolithium addition to a chiral ketimine, which because of competitive proton transfer proceeds with only modest yield in batch, can be significantly improved in flow. The transformation was discovered to be highly mixing-sensitive but remarkably temperature-independent in flow, enabling the continuous process to be performed under noncryogenic conditions. Experiments at the kilogram scale provided robust operating conditions that are amenable to implementing this chemistry for the manufacture of verubecestat (MK-8931), a drug candidate for the treatment of Alzheimer’s disease.

Cyclic Model for the Asymmetric Conjugate Addition of Organolithiums with Enoates

The chiral diether ligand controlled asymmetric conjugate addition of organolithiums to nona-2,7-dienedioates preferentially proceeds via the s-cis conformation with coordination of the carbonyl oxygen atom to the lithium to give a lithium E-enolate intermediate. Subsequent intramolecular conjugate addition of the enolate also proceeds via a cyclic transition state involving the lithium and the s-cis-enoate, resulting in trans,trans-trisubstituted cyclohexanes with high enantiomeric excesses and yields.

Cyclic Model for the Asymmetric Conjugate Addition of Organolithiums with Enoates

The chiral diether ligand controlled asymmetric conjugate addition of organolithiums to nona-2,7-dienedioates preferentially proceeds via the <i>s</i>-<i>cis</i> conformation with coordination of the carbonyl oxygen atom to the lithium to give a lithium <i>E</i>-enolate intermediate. Subsequent intramolecular conjugate addition of the enolate also proceeds via a cyclic transition state involving the lithium and the <i>s</i>-<i>cis</i>-enoate, resulting in <i>trans</i>,<i>trans</i>-trisubstituted cyclohexanes with high enantiomeric excesses and yields.

A short synthesis of (+)-β-lycorane by asymmetric conjugate addition cascade

The chiral diether ligand-controlled asymmetric conjugate addition of organolithiums to nona-2,7-dienedioate and subsequent intramolecular conjugate addition of the enolate intermediate gave all-trans trisubstituted cyclohexanes with high ee and yields. Using this methodology, an efficient short asymmetric total synthesis of (+)-β-lycorane was accomplished in 33% overall yield through five steps from the dienedioate.

Weinreb Amides

N-Methoxy-N-methylamides (Weinreb amides, WA) discovered by Weinreb and co-worker[1] can be prepared from easy available N,O-dimethylhydroxylamine hydrochloride (MeNHOMe·HCl) with for example: carboxylic acids, acid chlorides, esters, aldehydes, ketones (Scheme [1]).[2] These amides are interesting building blocks in synthetic chemistry. They are used to synthesize ketones, aldehydes or cyclic compounds by Grignard reaction, organolithium addition, reduction or acylation reaction of various compounds.[3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

Synthesis of ketones via organolithium addition to acid chlorides using continuous flow chemistry

An efficient method for the synthesis of ketones using organolithium and acid chlorides under continuous flow conditions has been developed.

Introducing deep eutectic solvents to polar organometallic chemistry: chemoselective addition of organolithium and Grignard reagents to ketones in air.

Despite their enormous synthetic relevance, the use of polar organolithium and Grignard reagents is greatly limited by their requirements of low temperatures in order to control their reactivity as well as the need of dry organic solvents and inert atmosphere protocols to avoid their fast decomposition. Breaking new ground on the applications of these commodity organometallics in synthesis under more environmentally friendly conditions, this work introduces deep eutetic solvents (DESs) as a green alternative media to carry out chemoselective additions of ketones in air at room temperature. Comparing their reactivities in DES with those observed in pure water suggest that a kinetic activation of the alkylating reagents is taking place, favoring nucleophilic addition over the competitive hydrolysis, which can be rationalized through formation of halide-rich magnesiate or lithiate species.

Synthesis, spectral, and anti-microbial studies of thioiminium iodides and amine hydrochlorides

To avoid the undesired deprotonation during the addition of organolithium and organomagnesium reagents to ketones, the thioiminium salts, easily prepared from lactams and amides are converted into 2,2-disubstituted and 2-monosubstituted amines by reaction with simple nucleophiles such as organocerium and organocopper reagents. The reaction of thioiminium iodides with organocerium reagents derived by transmetalation of corresponding lithium reagents with anhydrous cerium(III) chloride has been investigated. These thioiminium iodides act as good electrophiles and accept alkylceriums towards bisaddition. The newly synthesized amines have been characterized by 1H and 13C NMR, IR and mass spectra. The amines have been converted into their hydrochlorides and characterized by COSY. These hydrochlorides have been subjected to antimicrobial screening with clinically isolated microorganisms, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi and Candida albicans. The hydrochlorides show quite good activity against these bacteria and fungus.