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:...
51yield cu. 96%). The oil was dissolved in methylene chloride and activated MnO, (7 times the weight of the oil) was added. After shaking overnight, the mixture was filtered and the filtrate evaporated to yield 14b, 15b, 14c, 1% or 14d, 15d. Upon irradiation of the all-frans isomers of 9-demethyl-(14b), 13-demethyl-(14c) and 9,13-bisdemethylretinaI (14d), the 7-, 9-and 1 3 4 7 isomers were obtained in preparative amounts (5-30 mg) ( Table I). These isomers could be isolated by preparative HPLC. The assignment of the isomeric structures is based on the 360 MHz 'H N M R spectroscopic data (Tables 11, I11 and IV (Receiued June 4th, 1982) Abstract. Primary amines react with 2-(ethoxycarbonyl)-4,6-diphenylpyryliums to form pyridiniums. These are hydrolysed to 2-carboxylatopyridiniums which react with p-nitroso-N,N--dimethylaniline to give nitrones.
Die Umsetzung des Pyryliumions (I) mit primären Aminen wie z.B. (II) ergibt nach anschließender Hydrolyse die Carboxylate (III).
Die durch Hydrolyse der 2‐Ethoxycarbonyl‐pyridinium‐Salze erhaltenen Betaine (I) gehen die im Formelschema beschriebenen Reaktionen unter Bildung der Verbindungen (II), (IV), (VI), (VIII), (X) und (XI) ein.
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