In situ trapping of ortho lithiated benzenes containing electrophilic directing groups

Krizan, Timothy D.; Martin, J. C.

doi:10.1021/ja00357a034

Cited by 191 publications

(69 citation statements)

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“…De mEme, certains tlectrophiles se sont avCrts trks efficaces comme agent activateur d'une telle lithiation dont le CONR, le CSNR, le CONR2, l'oxazoline et le 0CONR2 (1). Dans ce demier cas, trois mtthodes ont ett utilistes pour Cviter la condensation du carbanion avec le produit de dCpart afin de permettre une concentration acceptable d'aryllithiurn avant l'addition d'un tlectrophile exteme (2): (i) l'utilisation d'une basse temperature de rtaction (-78°C ou moins); (ii) l'utilisation d'un tlectrophile sttriquement (oxazoline (3)) ou Clectroniquement (carbamate, amide (1 c)) dtactivt qui rCagit suffisamment lentement avec la base nucltophile (alkyllithium) ou avec l'anion formt, pour permettre l'attaque subsCquente d'un agent Clectrophilique; (iii) l'addition in situ de l'tlectrophile pour piCger l'intermtdiaire aryllithium immtdiatement aprks sa formation par une base trks sttriquement encombrk, le tktrarntthylpip6ridine amidure de lithium (LTMP) (2,4). Cette dernikre mtthode appliqute par Krizan et Martin permet d'obtenir des dtrivts benzonitrile-2 et (dicyano-1,3 benzene)-2 dans d'excellents rendements, comme dans le cas des rtsultats obtenus prtcedemrnent avec un Cchange halogenemttal (S), contmirement a ceux obtenus par une lithiation directe (lb, 6).…”

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Le lithio-2 naphtalène carbonitrile-1 et ses produits de substitutions

Fraser¹,

Savard²

1986

Can. J. Chem.

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Lithiation of 1-naphthonitrile provides the 2-lithio derivative exclusively. Reaction of this intermediate with ten different electrophiles produces 2-substituted derivatives in moderate to good yields. 2-Alkyl-1-naphthonitriles are readily lithiated and further alkylated to provide alkyl substituents modified at the α position. The pKa values for the hydrogen at the 2-position of 1-cyanonaphthalene and 2-methyl-1-cyanonaphthalene have been determined to be 36.3 and 28.5, respectively.

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Le lithio-2 naphtalène carbonitrile-1 et ses produits de substitutions

Fraser¹,

Savard²

1986

Can. J. Chem.

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“…It was found that direct access to difunctionalized quinoxaline derivatives of type 6 could be achieved by the addition of excessT MPLi (2,2 .4 equiv, À78 8C, 0.5 h) to 1, and subsequent trapping with chloroalkylsilanes [15] (2.5 equiv). This in situ trapping reaction occurs in the following way:f irst, the monolithiated intermediate reacts with the silyl electrophile.…”

Section: Resultsmentioning

confidence: 99%

Functionalization of Quinoxalines by Using TMP Bases: Preparation of Tetracyclic Heterocycles with High Photoluminescene Quantum Yields

Nafe

Herbert

Auras

et al. 2014

Chemistry A European J

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Tetracyclic heterocyclest hat exhibit high photoluminescence quantum yields were synthesized by anellation reactions of mono-, di-, and trifunctionalized 2,3-dichloroquinoxalines. Thus, treatment of 2,3-dichloroquinoxaline with TMPLi (TMP = 2,2,6,6-tetramethylpiperidyl) allows ar egioselective lithiationi np osition 5. Quenching with variouse lectrophiles (iodine, (BrCl 2 C) 2 ,a llylic bromide, acid chloride, aryl iodide)l eads to 5-functionalized 2,3-dichloroquinoxalines. Furtherf unctionalization in positions 6a nd 8c an be achieved by using TMPLi or TMPMgCl·LiCl furnishing ar ange of new di-and tri-functionalized 2,3-dichloroquinoxalines.T he chlorine atoms are readily substituted by anellation with 1,2-diphenols or 1,2-dithiophenols leading to as eries of new tetracyclic compounds. Thesem aterials exhibit strong, tunable optical absorption and emission in the blue and green spectralr egion.T he substituted O-heterocyclic compounds exhibit particularly high photoluminescence quantumy ields of up to 90 %, which renders them interestingc andidates for fluorescenceimaging applications.

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“…The introduction of the ditions [23] . two trimethylsilyl substituents was finally accomplished in a one-pot procedure [5] using the reagent combination chlorotrimethylsilane/lithium tetramethylpiperidide [19] to afford the bis(silylated) complex rac-5 in high yield. The crystal structure of rac-5 is depicted in Figure 5.…”

Section: Synthesis Of the Complexes Strategic Considerationsmentioning

confidence: 99%

Highly Regioselective Benzylic Deprotonation of Some (η ⁶ ‐Tetralin)‐ and (η ⁶ ‐ trans ‐Octahydroanthracene)Cr(CO) ₃ Derivatives: Is the Regioselectivity Stereoelectronically Controlled?

Volk

Bernicke

Bats

et al. 1998

Euro J of Inorganic Chem

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The regioselectivity of benzylic deprotonation of a number of conformationally restricted (arene)Cr(CO)3 complexes has been examined in order to ascertain whether stereoelectronic effects play a role in such reactions. The complexes rac‐5, rac‐6, rac‐7, rac‐8 and rac‐9 were diastereoselectively synthesized from the corresponding C2‐symmetric ligands (2,3‐disubstituted trans‐1,2,3,4‐tetrahydronaphthalene and trans‐1,2,3,4,4a,9,9a,10‐octahydroanthracene derivatives). Due to the desymmetrization caused by the Cr(CO)3 complexation, all four benzylic protons could be distinguished by 1H NMR and were assigned in all cases by a combination of H,H‐COSY spectra and the observation of H/D exchange at both exo positions (tert‐BuOK/[D6]DMSO). Deprotonation (n‐butyllithium)/deuteration (D2O or CF3CO2D) experiments revealed a very high, unforeseen regioselectivity in the cases of rac‐5 and rac‐7, while the other substrates showed a low selectivity (rac‐6) or could not be deuterated at all under these conditions (rac‐8, rac‐9). In the case of rac‐5, the regioselectivity of the deprotonation was further confirmed by acylation (AcCl) or alkylation (MeI) of the lithiated intermediate. These results clearly rule out the notion that the regioselectivity is due to the preferred abstraction of pseudoaxially oriented benzylic hydrogen atoms. The crystal structures of rac‐1, rac‐5 and rac‐7 suggest a possible link between the preferred conformation of the Cr(CO)3 tripod and the regioselectivity of the benzylic deprotonation. In analogy to a commonly accepted picture often used to explain the regioselectivity of nucleophile additions to (arene)Cr(CO)3 complexes, it was anticipated that those benzylic positions which are activated by an eclipsed CO ligand should be preferentially deprotonated (kinetically controlled). This (new) stereoelectronic model was corroborated by experiments using complexes rac‐60 and rac‐62, which were regioselectively deprotonated at the predicted position. In summary, it has been shown for the first time that the preferred conformation of the Cr(CO)3 tripod may have a directing influence on the regioselectivity of benzylic deprotonation in (arene)Cr(CO)3 complexes, at least in conformationally unambiguous situations where no obvious electronic effects are operative.

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In situ trapping of ortho lithiated benzenes containing electrophilic directing groups

Cited by 191 publications

References 0 publications

Le lithio-2 naphtalène carbonitrile-1 et ses produits de substitutions

Le lithio-2 naphtalène carbonitrile-1 et ses produits de substitutions

Functionalization of Quinoxalines by Using TMP Bases: Preparation of Tetracyclic Heterocycles with High Photoluminescene Quantum Yields

Highly Regioselective Benzylic Deprotonation of Some (η ⁶ ‐Tetralin)‐ and (η ⁶ ‐ trans ‐Octahydroanthracene)Cr(CO) ₃ Derivatives: Is the Regioselectivity Stereoelectronically Controlled?

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In situ trapping of ortho lithiated benzenes containing electrophilic directing groups

Cited by 191 publications

References 0 publications

Le lithio-2 naphtalène carbonitrile-1 et ses produits de substitutions

Le lithio-2 naphtalène carbonitrile-1 et ses produits de substitutions

Functionalization of Quinoxalines by Using TMP Bases: Preparation of Tetracyclic Heterocycles with High Photoluminescene Quantum Yields

Highly Regioselective Benzylic Deprotonation of Some (η 6 ‐Tetralin)‐ and (η 6 ‐ trans ‐Octahydroanthracene)Cr(CO) 3 Derivatives: Is the Regioselectivity Stereoelectronically Controlled?

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Highly Regioselective Benzylic Deprotonation of Some (η ⁶ ‐Tetralin)‐ and (η ⁶ ‐ trans ‐Octahydroanthracene)Cr(CO) ₃ Derivatives: Is the Regioselectivity Stereoelectronically Controlled?