Some novel reactions of pyridinium-2-carboxylate betaines

Abstract

Appropriate 2-ethoxycarbonylpyridinium salts are hydrolysed to 1 -aryl-4,6-diphenylpyridinium-2-carboxylate betaines which undergo thermal decarboxylation to afford, in the presence of acids, 1 -aryl-2,4-diphenylpyridinium salts. The intermediate ylides are captured by acid chlorides to yield 2-acylpyridinium salts and by CS, to give dithio analogues of the starting betaines. With bromine, the carboxylate betaine yields a 2,2'-bipyridyl bisquaternary salt.1 -Benzyl-4,6 -dip henylpyrid in ium -2-carboxy late with benzoyl chloride yields 2 -benzoyl-4,6 -diphenylpyridine and benzyl chloride. Benzaldehydes in place of PhCOCI, also gave 2-acylpyridines.The original objective of the present work was to induce aryl migration in intermediates of type (2), related to previously studied intramolecular nucleophilic attacks on N-aryl groups in suitably substituted pyridinium salts which resulted in easy displacement at the @so-carbon atom of the N-aryl group, and transfer to an oxygen,* ~u l p h u r ,~ or nitrogen ' s 4 atom. A r ( 1 ) I VAr ( 3 )While rearrangements (2+(3) were not achieved, several new reactions of the zwitterions (1) were disclosed. Transformations of type (lfi(2) have been reported by several authors, notably Ratts' (capture by RCHO) and Quast6*7 (capture by diazonium salts and by azides), and we now considerably extend the range of this reaction type.2-Ethoxycarbonyl-4,6-diphenylpyrylium tetrafluoroborate (4) reacted with aniline, p-toluidine, and benzylamine under standard conditions 8,9 to give the corresponding 1 -substituted pyridinium salts (5a-c) in high yields. These pyridinium-2-esters (5a-c) were hydrolysed by aqueous sodium hydroxide at ambient temperature to the 1 -substituted 4,6-diphenylpyridinium-2-carboxylate betaines (6a-c) in good yield. The crystalline carboxylate betaines (6a) and (6b) contain water of crystallisation, as shown by a singlet (2H) in their 'H n.m.r. spectra at 6 2.9, and by elemental analysis.' Anhydrous samples could not be obtained; both drying over magnesium sulphate in methylene chloride and attempted recrystallisation caused decomposition.1-Aryl-4,6-diphenylpyridinium-2-carboxylates (6a) and (6b) were converted into the 2-carboxy salts (8a) and (8b) in methylene chloride at 0 "C with tetrafluoroboric acid. The acid tetrafluoroborates were obtained analytically pure, free of water of crystallisation and in good yield. Their i.r. spectra showed the appearance of the BF4-band at 1050 em-' and a shift of the carbonyl stretching band from 1 650 cm-' in (6a) and (6b) to 1 720 em-' in (8a) and (8b).Decarboxylation of the 1 -Substituted 4,6-Diphenylpyridinium-2-carboxylates (6a+).-The 2-carboxy salts (8a) and (8b) are thermally unstable. When recrystallised from ethanol, the G O band at 1 720 cm-' was lost from the i.r. spectra, and elemental analysis confirmed loss of CO,. (5t(10): a, R = Ph; b, R = 4-MeC6H,; c, R = CH,Ph (7): A, X = I; B, X = Br; C, X = C1 (9): A, R' = Ph; R' = Me (11): a, Ar = Ph; b, Ar = p-MeC6H4; c, Ar = p-NO,C,H,; d, Ar = p-CIC,H, Scheme 2. Reagenfs:...

Organometallic Gas‐phase Ion Chemistry and Catalysis: Insights Into the Use of Metal Catalysts to Promote Selectivity in the Reactions of Carboxylic Acids and Their Derivatives

“…There has been considerable interest in developing decarboxylative versions of these catalytic reactions in which carboxylic acids are used as substrates Rodriguez&Goossen, 2011;Shang& Liu, 2011;Dzik et al, 2012;Cornella&Larrosa, 2012;Goossen&Goossen, 2013;Miao&Ge, 2014;Li et al, 2016;Satoh&Miura, 2016;Patra&Maiti, 2017;Perry& Larrosa, 2017;Sandfort et al, 2017;Campeau& Hazari, 2019;Daley& Topczewski, 2020;Moon&Lundgren, 2020). The solution-phase equivalent of the metal-mediated decarboxylative conversion of a carboxylate to a dithiocarboxylate discussed above (eqs 9, 32 and 33), however, appears (Katritzky et al, 1985;Schmidt et al, 2008).…”

“…Scheme 21: Examples of the transformation of a carboxylate to a dithiocarboxylate (Katritzky et al, 1985;Schmidt et al, 2008).…”

“…The solution-phase equivalent of the metal-mediated decarboxylative conversion of a carboxylate to a dithiocarboxylate discussed above (Equations 9,32,and 33), however, appears to be unprecedented in the literature. The only examples of such transformations are metal-free and involve zwitterionic substrates where the decarboxylated intermediate is an ylid (Scheme 21) (Katritzky et al, 1985;Schmidt et al, 2008).…”

“…Although this step has been discussed above within the context of the protodecarboxylation reaction, it is worth noting that the same catalysts that work well for step 1, are also readily regenerated via decarboxylation. (Katritzky et al, 1985;Schmidt et al, 2008). The decarboxylative cross-coupling reactions of carboxylic acid esters have been reviewed in terms of: their mechanistic features; the scope of the carboxylic acid ester substrates; and applications in total synthesis (Weaver et al, 2011).…”

Nucleophilic displacements of N-aryl and heteroaryl groups. Part 6. The rearrangement of 1-aryl-5,6,7,8-tetrahydro-8-oximino-2,6-diphenylquinolinium cations

“….-1 -Aryl-Zet hoxycarbony1-4,6-diphenylpyridinium tetrafluoroborates (4) were converted into the corresponding pyridinium acid chlorides (6) via the pyridinium betaines (5). 3 The reaction of (6a) and (6b) with benzylamine and neopentylamine gave the 2-(N-substituted carbamoy1)-pyridinium salts (7a--d), and with hydrazines (at O O C ) (6a-d) gave the 2-(substituted hydrazidocarbony1)pyridinium salts (8a-g) (Table 1). A complex mixture was obtained from the reaction of methylhydrazine with (6b) in the usual way; however, if the acid chloride (6b) was added slowly to a dichloromethane solution of methylhydrazine, the expected product (8e) was isolated.…”