Organolithium Intermediates Research Articles

Rapid flow synthesis of fenofibrate via scalable flash chemistry with in-line Li recovery

Flash chemistry controlled organolithium reactions allow redesigning the new economically affordable synthetic routes for life-saving drugs. However, microreactors limit their applications to extend industrial-level productivity. On the other hand, there has been little attention on recycling valuable elements from organic synthesis. In this work, a new compact monolithic metal microreactor was designed to successfully control the lifetime of short-lived organolithium intermediates at a large scale for sub-second scalable synthesis of fenofibrate as an FDA-approved drug for hypertriglyceridemia. Initially, the ultrafast chemistry of highly unstable ArLi intermediate was successfully explored for the synthesis of fenofibrate by its flow-controlled coupling reaction with 4-chlorobenzoyl chloride. As needed, by 3D metal printing of the CAD-CFD simulated works, eight laminated serpentine channels integrated with four flow distributors were constructed in a monolithic metal microreactor, leading to improved productivity up to 1.18 g min−1. At the in-line work-up step, the largely consumed Li was completely recovered for the potential recycling of valuable Li resources in a continuous-flow manner.

Convergent Synthesis of Isoindolines from Cyclic Imines and Organolithium Intermediates

Key words isoindolines - imines - lithiation - aryllithium

Synthesis and photophysical properties of 2-aryl-5-carbonyl indolizines

Herein we reported the synthesis of 20 novel fluorescent 5-carbonylated 2-arylindolizines derivatives through the reaction between organolithium intermediates with different electrophiles. To investigate the effects of the substituents on the wavelengths of electronic absorption spectra, fluorescence emission, quantum yield and Stokes shift, the photophysical properties of these molecules were evaluated. Maximum absorbance peaks were observed around 256–460 nm and maximum fluorescence emission around 485–548 nm. The fluorescence decay curves showed one or two decay times depending on the substituents with emission lifetime around 4–11 ns in methanol and 5–12 ns in DMSO. Quantum yield values ranged from 0.04 to 0.39 and Stokes shifts varied among 3.6–25 × 103cm−1. DFT calculations were also performed.

Kinetic Resolution by Lithiation: Highly Enantioselective Synthesis of Substituted Dihydrobenzoxazines and Tetrahydroquinoxalines

AbstractKinetic resolution provided a highly enantioselective method to access a range of 3-aryl-3,4-dihydro-2H-1,4-benzoxazines using n-butyllithium and the chiral ligand sparteine. The enantioenrichment remained high on removing the tert-butoxycarbonyl (Boc) protecting group. The intermediate organolithium undergoes ring opening to an enamine. The kinetic resolution was extended to give enantiomerically enriched substituted 1,2,3,4-tetrahydroquinoxalines and was applied to the synthesis of an analogue of the antibiotic levofloxacin that was screened for its activity against the human pathogen Streptococcus pneumoniae.

Continuous Flow as Enabling Technology: Synthesis of Heteroaromatic Sulfinates as Bench Stable Cross-Coupling Partners.

An enabling continuous flow setup for handling of unstable organolithium intermediates and synthesis of heteroaryl sulfinates on a multigram scale is described. The developed continuous flow process allows for the synthesis and simple isolation of heteroaryl sulfinates which are otherwise challenging to access in classical batch mode. The lithium sulfinate salts prepared by this method were shown to be efficient reaction partners in palladium catalyzed C(sp2)-C(sp2) cross-coupling to access medicinally relevant bis-heteroaryl motifs.

A Catalyst‐Free Amination of Functional Organolithium Reagents by Flow Chemistry

AbstractReported is the electrophilic amination of functional organolithium intermediates with well‐designed aminating reagents under mild reaction conditions using flow microreactors. The aminating reagents were optimized to achieve efficient C−N bond formation without using any catalyst. The electrophilic amination reactions of functionalized aryllithiums were successfully conducted under mild reaction conditions, within 1 minute, by using flow microreactors. The aminating reagent was also prepared by the flow method. Based on stopped‐flow NMR analysis, the reaction time for the preparation of the aminating reagent was quickly optimized without the necessity of work‐up. Integrated one‐flow synthesis consisting of the generation of an aryllithium, the preparation of an aminating reagent, and their combined reaction was successfully achieved to give the desired amine within 5 minutes of total reaction time.

A Catalyst-Free Amination of Functional Organolithium Reagents by Flow Chemistry.

Reported is the electrophilic amination of functional organolithium intermediates with well-designed aminating reagents under mild reaction conditions using flow microreactors. The aminating reagents were optimized to achieve efficient C-N bond formation without using any catalyst. The electrophilic amination reactions of functionalized aryllithiums were successfully conducted under mild reaction conditions, within 1 minute, by using flow microreactors. The aminating reagent was also prepared by the flow method. Based on stopped-flow NMR analysis, the reaction time for the preparation of the aminating reagent was quickly optimized without the necessity of work-up. Integrated one-flow synthesis consisting of the generation of an aryllithium, the preparation of an aminating reagent, and their combined reaction was successfully achieved to give the desired amine within 5 minutes of total reaction time.

Synthesis and kinetic resolution of substituted tetrahydroquinolines by lithiation then electrophilic quench.

Treatment of N-Boc-2-aryl-1,2,3,4-tetrahydroquinolines with n-butyllithium in THF at -78 °C resulted in efficient lithiation at the 2-position and the organolithiums were trapped with a variety of electrophiles to give substituted products. Variable temperature NMR spectroscopy gave kinetic data that showed that the rate of tert-butoxycarbonyl (Boc) rotation was fast (ΔG‡ ≈ 45 kJ mol-1 at -78 °C) and in situ ReactIR spectroscopy showed fast lithiation at -78 °C. By carrying out the lithiation in the presence of the chiral ligand sparteine, kinetic resolutions with very high levels of enantioselectivity were achieved. The resulting enantioenriched N-Boc-2-aryltetrahydroquinolines were converted to 2,2-disubstituted products without significant loss in enantiopurity. Most electrophiles add at the 2-position and the chemistry provides a way to access tetrahydroquinolines that are fully substituted alpha to the nitrogen atom. Notably, either enantiomer of the 2,2-disubstituted tetrahydroquinolines can be obtained with high selectivity from the same enantiomer of the chiral ligand. Unusually, when methyl cyanoformate was used as the electrophile, substitution occurred in the ortho position of the aryl ring attached at C-2. This change in regioselectivity on changing the electrophile was probed by deuterium isotope studies and by DFT calculations which suggested that the binding of the cyanoformate altered the structure of the intermediate organolithium. Secondary amine products can be prepared by removing the Boc group with acid or by inducing the Boc group to rearrange to the 2-position in the presence of triethylborane and this carbonyl N-to-C rearrangement occurs with retention of configuration from the intermediate enantiomerically enriched organolithium species.

Regioselective lithiation of 1‐benzylpyrazole derivatives: Synthesis of amides derived from pyrazole

A series of brominated 1‐benzylpyrazoles were deprotonated at the pyrazole 5‐position or the benzylic position on treatment with lithium diisopropylamide in tetrahydrofuran at low temperature. The obtained organolithium intermediates were subjected to reaction with Me3SiCl, t‐BuNCO, ClCONEt2 or ClCON(i‐Pr)2 affording the respective silanes or amides after hydrolysis.

Ortho‐Lithiation Reactions of O‐(3,n‐Dihalophenyl) N,N‐Diethylcarbamates: Synthesis of Dihalosalicylamides and 2,3,n‐Trihalophenol Derivatives

New dihalosalicylamides and trihalophenol derivatives have been synthesized from easily available O‐(3,n‐dihalophenyl) N,N‐diethylcarbamates by using a directed ortho‐metalation (DoM) strategy. The o‐lithiation reactions with sBuLi take place regioselectively at the doubly activated C‐2 position, which demonstrates the ability of O‐carbamates as directed metalating groups. In addition, highly functionalized arylnitriles were accessed from organolithium intermediates by using a tandem transnitrilation/SNAr reaction sequence.

ChemInform Abstract: α‐Lithiated Aryl Benzyl Ethers: Inhibition of [1,2]‐Wittig Rearrangement and Application to the Synthesis of Benzo[b]furan Derivatives.

AbstractLithiation of aryl benzyl ethers with tBuLi at low temperatures generates stable organolithium intermediates at the benzylic CH2‐group to give a variety of substituted ethers after quenching with electrophiles.

Integrated one-flow synthesis of heterocyclic thioquinazolinones through serial microreactions with two organolithium intermediates.

The synthesis of pharmaceutical compounds via short-lived intermediates in a microreactor is attractive, because of the fast flow and high throughput. Additionally, intermediates can be utilized sequentially to efficiently build up a library in a short time. Here we present an integrated microfluidic synthesis of biologically active thioquinazolinone libraries. Generation of o-lithiophenyl isothiocyanate and subsequent reaction with aryl isocyanate is optimized by controlling the residence time in the microreactor to 16 ms at room temperature. Various S-benzylic thioquinazolinone derivatives are synthesized within 10 s in high yields (75-98%) at room temperature. These three-step reactions involve two organolithium intermediates, an isothiocyanate-functionalized aryllithium intermediate, and a subsequent lithium thiolate intermediate. We also demonstrate the gram-scale synthesis of a multifunctionalized thioquinazolinone in the microfluidic device with a high yield (91%) and productivity (1.25 g in 5 min).

Integrated One‐Flow Synthesis of Heterocyclic Thioquinazolinones through Serial Microreactions with Two Organolithium Intermediates

AbstractThe synthesis of pharmaceutical compounds via short‐lived intermediates in a microreactor is attractive, because of the fast flow and high throughput. Additionally, intermediates can be utilized sequentially to efficiently build up a library in a short time. Here we present an integrated microfluidic synthesis of biologically active thioquinazolinone libraries. Generation of o‐lithiophenyl isothiocyanate and subsequent reaction with aryl isocyanate is optimized by controlling the residence time in the microreactor to 16 ms at room temperature. Various S‐benzylic thioquinazolinone derivatives are synthesized within 10 s in high yields (75–98 %) at room temperature. These three‐step reactions involve two organolithium intermediates, an isothiocyanate‐functionalized aryllithium intermediate, and a subsequent lithium thiolate intermediate. We also demonstrate the gram‐scale synthesis of a multifunctionalized thioquinazolinone in the microfluidic device with a high yield (91 %) and productivity (1.25 g in 5 min).

ChemInform Abstract: LiBF4 Integrated into [BMIm]BF4: An Ionic‐Liquid Metal Composite and Homogeneous Catalyst for Efficient Synthesis of Pyran‐Annulated Heterocycles.

The ionic liquid [BMIm]BF4 doped with LiBF4 was found to efficiently catalyze the three-component reaction between isocyanides, acetylenic esters and enols or phenols at room temperature, leading to rapid synthesis of 2-aminopyran-annulated systems in fairly high yields. Efficiency of this catalysis and its benefits in terms of improved yields and reaction times could be ascribed to involvement of relatively stable organolithium intermediates which make the reaction more feasible. The ionic solution tolerates a significant amount of dissolved LiBF4, while remaining fluid at room temperature to serve as solvent for the organic substrates. It retains its initial integrity after use and recovery, as it could be recycled several times without appreciable catalytic decrements. The catalytic activity of the ionic composite is completely lost in the absence of LiBF4. Copyright © 2014 John Wiley & Sons, Ltd.

LiBF4integrated into [BMIm]BF4: an ionic‐liquid metal composite and homogeneous catalyst for efficient synthesis of pyran‐annulated heterocycles

The ionic liquid [BMIm]BF4doped with LiBF4was found to efficiently catalyze the three‐component reaction between isocyanides, acetylenic esters and enols or phenols at room temperature, leading to rapid synthesis of 2‐aminopyran‐annulated systems in fairly high yields. Efficiency of this catalysis and its benefits in terms of improved yields and reaction times could be ascribed to involvement of relatively stable organolithium intermediates which make the reaction more feasible. The ionic solution tolerates a significant amount of dissolved LiBF4, while remaining fluid at room temperature to serve as solvent for the organic substrates. It retains its initial integrity after use and recovery, as it could be recycled several times without appreciable catalytic decrements. The catalytic activity of the ionic composite is completely lost in the absence of LiBF4. Copyright © 2014 John Wiley & Sons, Ltd.

Synthesis of 1‐Substituted Tetrahydroisoquinolines by Lithiation and Electrophilic Quenching Guided by In Situ IR and NMR Spectroscopy and Application to the Synthesis of Salsolidine, Carnegine and Laudanosine

The lithiation of N-tert-butoxycarbonyl (N-Boc)-1,2,3,4-tetrahydroisoquinoline was optimized by in situ IR (ReactIR) spectroscopy. Optimum conditions were found by using n-butyllithium in THF at -50 °C for less than 5 min. The intermediate organolithium was quenched with electrophiles to give 1-substituted 1,2,3,4-tetrahydroisoquinolines. Monitoring the lithiation by IR or NMR spectroscopy showed that one rotamer reacts quickly and the barrier to rotation of the Boc group was determined by variable-temperature NMR spectroscopy and found to be about 60.8 kJ mol(-1), equating to a half-life for rotation of approximately 30 s at -50 °C. The use of (-)-sparteine as a ligand led to low levels of enantioselectivity after electrophilic quenching and the "poor man's Hoffmann test" indicated that the organolithium was configurationally unstable. The chemistry was applied to N-Boc-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline and led to the efficient synthesis of the racemic alkaloids salsolidine, carnegine, norlaudanosine and laudanosine.

Practical Enantioselective Arylation and Heteroarylation of Aldehydes with In Situ Prepared Organotitanium Reagents Catalyzed by 3‐Aryl‐H8‐BINOL‐Derived Titanium Complexes

A highly efficient and practical method for the catalytic enantioselective arylation and heteroarylation of aldehydes with organotitanium reagents, prepared in situ by the reaction of aryl- and heteroaryllithium reagents with ClTi(OiPr)3, is described. Titanium complexes derived from DPP-H8 -BINOL (3d; DPP=3,5-diphenylphenyl) and DTBP-H8 -BINOL (3e; DTBP=3,5-di-tert-butylphenyl) exhibit excellent catalytic activity in terms of enantioselectivity and turnover efficiency for the transformation, providing diaryl-, aryl heteroaryl-, and diheteroarylmethanol derivatives in high enantioselectivity at low catalyst loading (0.2-2 mol%). The reaction begins with a variety of aryl and heteroaryl bromides through their conversion into organolithium intermediates by Br/Li exchange with nBuLi, thus providing straightforward access to a range of enantioenriched alcohols from commercially available starting materials. Various 2-thienylmethanols can be synthesized enantioselectively by using commercially available 2-thienyllithium in THF. The reaction can be carried out on a 10 mmol scale at 0.5 mol% catalyst loading, demonstrating its preparative utility.

Inter- and intramolecular enantioselective carbolithiation reactions

In this review we summarize recent developments in inter- and intramolecular enantioselective carbolithiation reactions carried out in the presence of a chiral ligand for lithium, such as (−)-sparteine, to promote facial selection on a C=C bond. This is an attractive approach for the construction of new carbon–carbon bonds in an asymmetric fashion, with the possibility of introducing further functionalization on the molecule by trapping the reactive organolithium intermediates with electrophiles.

Nucleophilic addition of regioselectively lithiated indoline with aldimines for the syntheses of 2- and 7-indolinyl methanamine derivatives

Indolines bearing different N-protecting groups (N-Tbf and N-Boc) were deprotonated regioselectively at C-2 (sp3 hybridized ortho-H) and C-7 (sp2 hybridized para-H) of the indoline ring, respectively. The generated organolithium intermediates reacted with aldimines to give the desired products in good yields with excellent anti-diastereoselectivities (>99:1). The produced N-Ts-(1-Tbf-indolin-2-yl)methanamine was facilely transformed to a fused heterocyclic compound.

A method for the synthesis of 2-aminobenzoxazoles

A synthesis of 2-aminobenzoxazoles from the parent C–H compound is described. The procedure involves deprotonation at the 2-position of the benzoxazole and quenching the intermediate organolithium species with a halogen electrophile. The 2-halobenzoxazole is then treated in the same pot with an amine nucleophile to afford the desired product. The substrate scope and selectivity of the reaction are presented. The method is operationally simple and provides access to a variety of amine products bearing additional nucleophilic heteroatoms.