On the reactivity of pyridines towards carbocations

Dembinski, A; Yaǧcı, Yusuf; Schnabel, W.

doi:10.1016/0032-3861(93)90063-g

Cited by 6 publications

(3 citation statements)

References 8 publications

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“…Therefore, their reactivities cannot be characterized readily with a method that uses 266 nm pump pulses. Rate constants of the reactions of photolytically generated carbocations with pyridines could previously only be determined when the employed precursors incorporated a highly conjugated π system which absorbed at λ > 300 nm . The reactivity data acquired in this study will subsequently be employed to determine the nucleophilicity parameters, N and s N , for the pyridines 4 – 8 according to the linear free energy relationship eq , which allows us to predict second-order rate constants, k 2 , for polar organic reactions with one electrophile-specific parameter, E , and two solvent-dependent nucleophile-specific parameters, N and s N …”

Section: Introductionmentioning

confidence: 99%

Photogeneration of Benzhydryl Cations by Near-UV Laser Flash Photolysis of Pyridinium Salts

Nigst

Ammer²,

Mayr³

2012

J. Phys. Chem. A

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Laser flash irradiation of substituted N-benzhydryl pyridinium salts yields benzhydryl cations (diarylcarbenium ions) and/or benzhydryl radicals (diarylmethyl radicals). The use of 3,4,5-triamino-substituted pyridines as photoleaving groups allowed us to employ the third harmonic of a Nd/YAG laser (355 nm) for the photogeneration of benzhydryl cations. In this way, benzhydryl cations can also be photogenerated in the presence of aromatic compounds and in solvents which are opaque at the wavelength of the quadrupled Nd/YAG laser (266 nm). To demonstrate the scope and limitations of this method, the rate constants for the bimolecular reactions of benzhydryl cations with several substituted pyridines were determined in acetonitrile and with water in acetone. The obtained data agree with results obtained by stopped-flow UV-vis spectroscopic measurements. The rate constants for the reaction of the 4,4'-bis[methyl(2,2,2-trifluoroethyl)amino]benzhydrylium ion with 4-(dimethylamino)pyridine were also determined in dimethyl sulfoxide, N,N-dimethylformamide, and acetone. From the second-order rate constants, we derived the nucleophilicity parameters N and s(N) for the substituted pyridines, as defined by the linear free energy relationship, log k(2) = s(N)(N + E).

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Section: Introductionmentioning

confidence: 99%

Photogeneration of Benzhydryl Cations by Near-UV Laser Flash Photolysis of Pyridinium Salts

Nigst

Ammer²,

Mayr³

2012

J. Phys. Chem. A

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“…28 Rate constants between the vinylic cations and DTBP are the lowest among all pyridines. 29 Enolizable aldehydes and ketones afford enolic triflates with triflic anhydride and these nonnucleophilic bases; 30 such enolic esters are important in carbohydrate research; 31 other similar esters can be used for palladium-catalyzed couplings. 32 Radical cations of thianthrene 33 or anthracene 34 act as one-electron oxidants in the presence of these nonnucleophilic bases.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, the electrochemical polymerization of pyrrole is inhibited by DTBP, owing to proton scavenging . Rate constants between the vinylic cations and DTBP are the lowest among all pyridines . Enolizable aldehydes and ketones afford enolic triflates with triflic anhydride and these nonnucleophilic bases; such enolic esters are important in carbohydrate research; other similar esters can be used for palladium-catalyzed couplings .…”

Section: Introductionmentioning

confidence: 99%

Simple Synthesis of a Weak Nucleophilic Base (4-Ethyl-2,6-diisopropyl-3,5-dimethylpyridine) Evidencing a Double Janus Group Effect

et al. 2003

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By analogy with 2,6-di-tert-butylpyridine and its 4-methyl-substituted derivatives, which are nonnucleophilic bases, 4-ethyl-2,6-diisopropyl-3,5-dimethylpyridine (4) is also such a base. The isopropyl groups (Janus-like groups) are forced by the neighboring methyl groups to turn their "tert-butyl-analogue face" toward the heteroatom, thereby protecting it sterically against electrophilic attack. The synthesis proceeds in two stages via the corresponding pyrylium salt 3 that is obtained by alkene diacylation. X-ray data for 4, its picrate, and the hexafluorophosphate of 3 confirm that the ground-state conformation agrees with the Janus effect prediction. The chemical behavior of 4 indicates that it is indeed a weak nucleophilic base, which is able to substitute the nonnucleophilic bases in organic syntheses. The compound 3 reacts at normal pressure with methylamine or ethylamine, forming N-alkylpyridinium salts. The cationic polymerization of isobutene in the presence of 4 was also investigated.

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2,6-Di-tert-butyl-4-methylpyridine (DTBMP)

Balaban

2004

Encyclopedia of Reagents for Organic Synthesis

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On the reactivity of pyridines towards carbocations

Cited by 6 publications

References 8 publications

Photogeneration of Benzhydryl Cations by Near-UV Laser Flash Photolysis of Pyridinium Salts

Photogeneration of Benzhydryl Cations by Near-UV Laser Flash Photolysis of Pyridinium Salts

Simple Synthesis of a Weak Nucleophilic Base (4-Ethyl-2,6-diisopropyl-3,5-dimethylpyridine) Evidencing a Double Janus Group Effect

2,6-Di-tert-butyl-4-methylpyridine (DTBMP)

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