Deprotonated pyridines addition

Product studies have demonstrated that I-phenyl and 1,1-diarylalkene radical cations react with nitrogen-centered nucleophiles such as amines and pyridines by both addition and deprotonation. The addition reactions occur by a mechanism analogous to that shown in Scheme I for methanol addition. Deprotonation by an amine or pyridine base is an alternate possibility for radical cations derived from 2-alkyl-substituted alke-nes and leads to an allylic radical (Eq. 19). Reduction of this radical by the sensitizer radical anion generates an anion that is protonaled at either the original position to regenerate starting... 

In 2011, Driver and coworkers synthesized dimebolin by utilizing a ruthenium-catalyzed nitrenoid insertion reaction that they developed (Scheme 16.10) [21]. Azide 49 was readily prepared from 48 by a two-step sequence, consisting of treatment with sodium nitrite and sodium azide, and alkylation of pyridine. Addition of catalytic RuClg hydrate to 49 formed putative ruthenium nitrenoid 50 [22], which then underwent regioselective C-H amination at the C4 position of the pyridinium ion to give y-carbolinium salt 51 in 91% yield. Deprotonation of the N-H group of 51, followed by alkylation with 52, appended the requisite pyridine... 

The influence of different additives on the apparent pKa values of diphenylmethane, 4-methyl-pyridine and the deprotonation rate of triphenylmethane was investigated 3 TM EDA caused the highest enhancement. 

Explain what happens to (a) the pH of a solution of phosphoric acid after the addition of solid sodium dihydrogen phosphate (b) the percentage deprotonation of HCN in a hydrocyanic acid solution after the addition of hydrobromic acid (c) the concentration of H ions when pyridinium chloride is added to an aqueous solution of the base pyridine. 

A similar (but somewhat less obvious) dichotomy results in the simultaneous ring and sidechain substitution of durene. Thus in this charge-transfer nitration, the addition of N02 to the cation radical DUR+- (72) occurs in competition with its deprotonation (73), in which the pyridine has been shown to act as a base (Masnovi et al., 1989) (Scheme 15). [Note that deprotonation of DUR+- also leads to aromatic dimers via the subsequent (oxidative) substitution of the benzylic radical formed in (73) (Bewick et al., 1975 Lau and Kochi, 1984).]... 

The pffa of 3-methylpyridine, whose anion cannot be delocalized onto N, is closer to that of toluene, and deprotonation gives only low yields with most bases. However, with a combination of BuLi and lithiodimethylaminoethanol (LiDMAE) deprotonation is quantitative but yields products 561 arising from apparent lithiation a to N (Scheme 224) Trying to force lateral lithiation of pyridines is generally doomed to failure, as ring lithiation or nucleophilic addition nsnally takes place first . 

Early work by Abramovitch showed that treatment of 3- N,N-diethylaminosulfonyl)pyridine with PhLi leads to C-2 addition (65CJC1752), a result which discouraged used of alkyllithiums for deprotonation of pyridyl sulfonamides. In a detailed investigation, Queguiner found that (a) the piperidine sulfonamide is the best DMG (b) LDA is a useful metalation base in 2 equiv. amount (80% yield) rather than 1 equiv. (27% yield) on the basis of PhCHO quench (83S822). 

Addition of amide (122, H4L) and Na2C03 to a boiling solution of CrCl3-6H20 in pyridine results in formation of the complex [Cr(HL)py2]2-2py (154), which contains chromium(IU) coordinated to the amide oxygen and deprotonated amide nitrogen of different molecules.519 This is the first reported example of chromium(III) coordinated ito a nitrogen of a deprotonated amide. The structure consists of discrete dimers and disordered solvent molecules of pyridine. 

The reaction was carried out in CH3CN-Et4NC104 with addition of pyridine as base, using controlled potential electrolysis and a divided cell. The yield of (33) varied greatly, depending on the method of electrolysis. Oxidation of 32 in the presence of pyridine gave 33 in 60-85% yield, whereas the electrolysis without pyridine lowered the yield to 10-20%, and products of hydrolysis, because of accumulation of the acid in the anodic compartment, were identified. The mechanism of the reaction proposed on the basis of electroanalytical results involves the cyclization of the radical-cation or its deprotonation as the rate-determining step.78... 

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