1,6‐ and 1,7‐naphthyridines. I. Rearrangement of quinolinimidoacetic acid derivatives

Abstract

The reaction of N‐substituted quinolinimides 1a‐d with sodium alkoxides afforded a mixture of 1,6‐naphthyridines 2 and 1,7‐naphthyridines 3 which were isolated by chromatographic methods. Structure assignment for each pair of isomers was made by comparison of their 1H nmr spectra with those of picolinamide and nicotinamide. When esters 1a‐c were treated with alkoxides from primary alcohols, other than that of the ester, total transesterification took place. Experimental results suggest that transesterification occurs in open intermediary species.

1,6‐ and 1,7‐naphthyridines III. 13C‐NMR analysis of some hydroxy derivatives

“…The results obtained by means of 1D nOe difference experiments in dimethyl-d 6 sulfoxide (DMSO-d 6 ) allowed unambiguous assignment of isomers 2 and 3 that confirmed both the proposed structures and the assignment of the pyridine hydrogens carried out previously [1]. Thus, using isopropyl esters 2c and 3c as models, in the compound of higher Rf a positive nOe is observed between the enol hydroxyl and the Hc of the pyridine nucleus (Scheme II), evidencing that it is actually 1,7-naphthyridine 3c [4].…”

“…Likewise, the contribution of structures VI and VII leads to greater chemical shifts of the Cb,d in the 1,7-vs. 1,6-series. These results show that the secondary carbon pattern (Ca,b,c) is similar to that of the corresponding hydrogen atoms, as was also explained on the basis of electronic effects alone [1,3].…”

“…Literature procedures were followed in the preparation of compounds 1-5 [1,3]. Purity was ascertained by tlc experiments on aluminium sheets Silica gel 60 F 254 using five different solvent mixtures.…”

“…In previous work, we studied the alkoxide-catalyzed rearrangement of quinolinimidoacetic acid derivatives 1, that leads to the formation of two isomeric compounds, 7-substituted 8-hydroxy-1,6-naphthyridin-5(6H)ones 2 and 6-substituted 5-hydroxy-1,7-naphthyridin-8(7H)ones 3 (Scheme I) [1], which were separated by chromatographic methods. Structural assignment of these compounds was carried out by comparison of 1 H-NMR spectra with those of model compounds (nicotinamide and picolinamide).…”

Mass spectrometry of aromatic cyclic imides and amides. Part II: electron ionization induced decomposition of N-substituted 3,4-pyridinedicarboximides

“…The conditions are: ionizing energy, 70 eV; collision gas: argon at a pressure of 2.04 mTorr; collision energy: 16v. Compounds 1a,4a, 16 1c,1e-g 3d and 4b-d,g 17 were synthesized according literature procedures. Preparation and analytical characterization of new compounds are described below.…”