Lithium–Bromide Exchange versus Nucleophilic Addition of Schiff's base: Unprecedented Tandem Cyclisation Pathways

Orr, Samantha A.; Border, Emily Chantelle; Andrews, Philip C.; Blair, Victoria L.

doi:10.1002/chem.201902140

Cited by 4 publications

(4 citation statements)

References 63 publications

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“…Starting with a bromo‐substituted imine, this first step was a lithium–bromide exchange performed in THF at −100 °C for 15 min, the reaction was then allowed to warm to room temperature allowing an internal 1,2 nucleophilic addition resulting in a new C−C bond formation, yielding the desired bicyclic product. Similar cyclisation pathways initiating from lithium–bromide exchange have been witnessed as reported recently by our group [56] (see section 3).…”

Section: Addition Reactionssupporting

confidence: 85%

“…In a similar approach our group have recently reported the isolation of synthetically valuable iso ‐indolinones and N‐substituted anthracene complexes via lithium–bromide exchange reactivity of aromatic Schiff bases [56] . Reaction of t BuLi with ortho ‐bromo‐substituted diaryl‐imines uncovered competitive Li–Br exchange and nucleophilic addition pathways at play, highly dependent on a range of reaction parameters including, solvent, stoichiometry, temperature and sterics (Scheme 16).…”

Section: Metathesismentioning

confidence: 99%

“…In as imilara pproach our group have recently reported the isolation of synthetically valuable iso-indolinonesa nd N-substituted anthracene complexes via lithium-bromide exchange reactivity of aromatic Schiff bases. [56] Reaction of tBuLi with ortho-bromo-substituted diaryl-imines uncovered competitive Li-Br exchange andn ucleophilic addition pathways at play, highly dependent on ar ange of reaction parameters including, solvent, stoichiometry,t emperature and sterics (Scheme16). The resultant cyclised products are formed via at wo-step 1,2 nucleophilic addition process of the lithiated iminei ne ither a "head-to-head" or "head-to-tail" manner,t oa fford the iso-indolinonesa nd N-phenyl-anthracenes,r espectively.I solation and X-ray crystallography confirmedt he di-lithio-anthracene intermediate (Figure 3).…”

Section: Metathesismentioning

confidence: 99%

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Main Group Metal‐Mediated Transformations of Imines

Orr

Andrews

Blair

2020

Chemistry A European J

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Main‐group‐metal‐mediated transformations of imines have earned a valued place in the synthetic chemist's toolbox. Their versatility allows the simple preparation of various nitrogen containing compounds. This review will outline the early discoveries including metallation, addition/cyclisation and metathesis pathways, followed by the modern‐day use of imines in synthetic methodology. Recent advances in imine C−F activation protocols are discussed, alongside revisiting “classic” imine reactivity from a sustainable perspective. Developments in catalytic methods for hydroelementation of imines have been reviewed, highlighting the importance of s‐block metals in the catalytic arena. Whilst stoichiometric transformations in alternative reaction media such as deep eutectic solvents or water have been summarised. The incorporation of imines into flow chemistry has received recent attention and is summarised within.

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Section: Addition Reactionssupporting

confidence: 85%

Section: Metathesismentioning

confidence: 99%

Section: Metathesismentioning

confidence: 99%

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Main Group Metal‐Mediated Transformations of Imines

Orr

Andrews

Blair

2020

Chemistry A European J

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“…Several methodologies are developed for these transformations . The important strategies include: (i) photocatalytic alkylation of imines enabled by organic photocatalysts or metal catalysts; (ii) nucleophilic additions of the CN bond of imines by dialkylzinc, Grignard reagents, and organolithium complexes . Several review articles have been published on this topic .…”

Section: Introductionmentioning

confidence: 99%

Nucleophilic Addition and α-C–H Substitution Reactions of an Imine Mediated by Dibutylmagnesium and Organolithium Reagents

Dang

Wang

et al. 2021

Organometallics

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A series of nucleophilic addition reactions and α-C–H substitution reactions of an imine-containing ligand 2-(2-((((1H-pyrrol-2-yl)methylene)amino)methyl)-1H-pyrrol-1-yl)-N,N-dimethylethan-1-amine (HL1) were reported. The reactions of HL1 with 0.5 and 2 equiv of n Bu2Mg, respectively, gave two complexes of compositions [Mg(L1)2] (1) and [Mg2(L2)2] (2) (H2L2 = N-((1-(2-(dimethylamino)ethyl)-1H-pyrrol-2-yl)methyl)-1-(1H-pyrrol-2-yl)pentan-1-amine). The nucleophilic addition of n Bu2Mg to the CN bond of the HL1 ligand occurred in the process for the formation of 2. Treatment of HL1 with 2 and 1 equiv of n BuLi generated [Li2(L3)2] (3) (HL3 = 2-(2-(((1-(1H-pyrrol-2-yl)pentylidene)amino)methyl)-1H-pyrrol-1-yl)-N,N-dimethylethan-1-amine) and [Li2(L1)2] (4). An α-C–H substitution of the HCNR moiety of the HL1 ligand triggered by n BuLi was discovered in the preparation of 3. The formation of 3 demonstrates a new concept for the C–C coupling that involved inert C–H bond activation of HCNR skeleton. The reactions of HL1 with MeLi, sec-BuLi, and tert-BuLi, respectively, were also examined. The products for both the nucleophilic addition of organolithium reagents to the CN bond and α-C–H substitution of the HCNR moiety of the HL1 ligand were determined. The mechanisms for the formations of 2 and 3 were rationalized by DFT calculations. The hydroboration reactions catalyzed by 2 were investigated, and these reactions characterize ample substrate scope, very good yields, and high selectivity.

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Advancing Air‐ and Moisture‐Compatible s‐Block Organometallic Chemistry Using Sustainable Solvents

et al. 2021

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Challenging conventional wisdom that s-block organometallic reagents such as Grignard or organolithiums need to be used under protecting inert atmosphere (N 2 or Ar), employing dry organic solvents with a strict temperature control, this Minireview focusses on recent advances on the use of these commodity reagents while operating under air, at room temperature and in the presence of moisture. Key for the success of these approaches has been the use of the following sustainable solvents: i) water; ii) Deep Eutectic Solvents (DESs); or iii) biomass-derived polyols (like glycerol) or ethereal solvents [i. e., 2-MeTHF or cyclopentyl methyl ether (CPME)]. The versatility of these air and moisture compatible synthetic protocols has been demonstrated for a myriad of key organic transformations, including nucleophilic additions of RLi/RMgX reagents to unsaturated organic molecules (i. e., ketones, imines, esters, amides or nitriles) as well as ortho-and lateral lithiation of aromatic substrates, Pd catalysed cross-couplings and anionic polymerisation of styrenes. Extension of these studies to lithium amides (LiNR 2 ) or phosphides (LiPPh 2 ) has enabled the development of more sustainable and efficient methods for CÀ N and CÀ P bond forming processes. These unconventional s-block metal mediated transformations have also been successfully incorporated in one-pot tandem processes in combination with transition-metal and organo-catalysis. Remarkably, in some cases the conversions and chemoselectivities observed are superior to those detected in common toxic organic solvents, while working under inert atmosphere conditions with strict temperature control. The key role played by the choice of solvent in these transformations and how it can affect the constitution of the s-block organometallic species present in solution is also discussed.

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Lithium–Bromide Exchange versus Nucleophilic Addition of Schiff's base: Unprecedented Tandem Cyclisation Pathways

Cited by 4 publications

References 63 publications

Main Group Metal‐Mediated Transformations of Imines

Main Group Metal‐Mediated Transformations of Imines

Nucleophilic Addition and α-C–H Substitution Reactions of an Imine Mediated by Dibutylmagnesium and Organolithium Reagents

Advancing Air‐ and Moisture‐Compatible s‐Block Organometallic Chemistry Using Sustainable Solvents

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