¹³C NMR investigation of some hetero‐ring substituted 2‐ and 4‐quinolone systems

Abstract

A series of 2-and 4-quinolones substituted in the hetero-ring have been evaluated using 13C NMR techniques. Substituent effects are discussed as an aid to evaluation of potential tautonnerimtion in the 2-quinolone systems. The observed substituent shifts for systems having a hydroxy function at the 4-position in the 2-quinolones can be explained without implementing the tautomerism to a 4-quinolone.During the course of some synthetic investigations involving the preparation of substituted 2-and 4-quinolones, it became necessary to use 13C NMR for the analysis of the products. A search of the literature for model systems revealed that very little work has been done in this area, other than for the parent compounds and some ring methylated derivatives.' It seemed of interest to extend these studies to include compounds substituted in the hetero ring, such as 1 and 2 shown below.From the data given in Table 1 it can readily be observed that several of the I3C chemical shifts vary over a large range. The C-2 and C-3 chemical shifts, which range over 18ppm and 32ppm, respectively, can be explained on the basis of substituent shifts inherent to the type of substitution involved. The N-CH, and C-4 chemical shifts also show a large range, and in both cases the shifts are to higher field than the parent system. The upfield substituent shift reflects the steric environment of these carbons. Interestingly, the N-CH, resonance seems sensitive to electronic effects, as seen in a comparison of shifts for l c and Id. The remaining carbon chemical shifts are much less affected by substituents at C-2 and C-3, with C-4a and C-6 showing the largest variations. In all, the substituent chemical shifts for 1 appear to be unexceptional and, therefore, should be useful for the analysis of the tautomerism possibilities in the 2-quinolones discussed below. 4-QuinolonesThe chemical shift data are given in Table 1, and the system numbering is shown above. The assignments are relatively straightforward and were made by comparison with the parent compound and the unmethylated material previously assigned in the literature.' 2-Quinolones

Abkömmlinge der 3‐Chinolincarbonsäure mit Sauerstoffsubstitution in Stellung 4, 5 and 8: Synthese, Reaktionen, NMR.‐Studien

“…7-Substituenten auf die Verschiebungen im Benzolring sowie auf der angenommenen weitgehenden Lagekonstanz der Signale von C (2) bis C (4) im Pyridonring. Uber die chemischen Verschiebungen einiger 4-Chinolone wurde kurzlich berichtet [8] [9].…”

“…Die 6-Substitution von 67 folgt dann eindeutig aus dem Fehlen der Kopplung entsprechend "J(fI-C(6)) beim Signal von C(10) und dem Auftreten von "J(H-C (7)) beim Signal von C (9). Umgekehrt wird bei der 7-substituierten Verbindung 68 keine Kopplung von C(9) rnit H-C(7) (verbreitertes Dublett), dafur eine solche von C ( 10) Hingegen koppelt das Proton der Hydroxygruppe an C (8) in keiner Verbindung mit C (7), C (8) oder C (9).…”

“…Umgekehrt wird bei der 7-substituierten Verbindung 68 keine Kopplung von C(9) rnit H-C(7) (verbreitertes Dublett), dafur eine solche von C ( 10) Hingegen koppelt das Proton der Hydroxygruppe an C (8) in keiner Verbindung mit C (7), C (8) oder C (9). Dieses unterschiedliche Verhalten erklart sich daraus, dass an der ctnormalen)) 8-Hydroxygruppe unter dem Einfluss der Aciditat der H-C (6) H-C (7) HO-C (5) H3CO-C (5) HO-C (8) H,CO-C(8)…”

Cytotoxic Constituents from Aquilegia ecalcarata

“…The 13 C-NMR spectrum showed 14 carbon signals, five attributed to the furan group. The other nine carbon signals, especially the carbonyl signal at d = 163.2, were characteristic of 2-quinolone group [4]. The long-range correlation between the signals at H-3¢ (d = 7.16) and C-4 (d = 146.…”

Fused Quinoline Heterocycles V. Synthesis of Novel 1,2,3,5,6-Pentaazaaceanthrylene Derivatives

“…The isomeric quinolin-4-one structure (5) could be excluded because the IR spectrum showed significantly an amide carbonyl function at 1665 cm -1 ; 11,12 4-quinolinones generally have carbonyl absorptions below 1600 cm -1 . [13][14][15] The pyrazolo [4,3-c]quinolines 2 served as a starting point for the construction of novel tetracyclic systems incorporating both a pyrimidine nucleus and a pyrazoloquinoline moiety. Thus, the reaction of compound 2 with phenyl isothiocyanate in dry pyridine at reflux for 15 min led to the novel 1,5diphenyl-1,5-dihydro-1,2,3,5,6-pentaazaaceanthrylene-4(3H)thione (7).…”