1,5-Naphthyridines and their n-oxides III. Synthesis and biological activity of some mono- and disubstituted 1,5-naphthyridines and their n-oxides
In order to search for biologically active compounds in the 1,5-naphthyridine series, we synthesized 2-mercaptoand 2-(4'-aminobenzenesulfonamido)-l,5naphthyridines and some of their 6-substituted derivatives. 2-(4'-Aminobenzenesulfonamido)-l,5-naphthyridine (I) was obtained by reaction of 2-amino-l,5naphthyridine with 4-carbomethoxyaminobenzenesulfonyl chloride in pyridine with subsequent saponification of the carbomethoxy group in the resulting 2-(4'carbomethoxyaminobenzenesulfonamido)-l,5-naphthyridine (II).
Tautomerism of 3-alkoxycarbonylmethylene-2-oxo-1,2,3,4-tetrahydroquinoxaline derivatives
The compound previously formulated as ethyl 1,2-dihydro-2-oxoquinoxalin-3-ylacetate has the isomeric structure 3-ethoxycarbonylmethylene-2-oxo-1,2,3,4-tetrahydroquinoxaline in the solid state. In solution the 1-methyl derivative has been shown by nuclear magnetic resonance studies to exist as a tautomeric mixture of unsaturated and saturated esters.
Spin-spin coupling between side-chain and ring protons and the effect of electron delocalization on allylic coupling
The side-chain-ring coupling constants3 in the three isomeric tetrachlorotoluenes are Jortho 0.63±0.02 c/s, Jmeta 0.36±0.02 c/s, and Jpara 0.63±0.01 c/s. The magnitudes of side-chain coupling constants in benzene derivatives are discussed. In symmetrical six-membered aromatic and heterocyclic compounds the magnitude of the ortho side-chain coupling constants is approximately 0.6 c/s but varies from less than 0.3 cis to 1.1 c/s in molecules where some bond localization occurs. Ortho side-chain coupling constants in five-membered heterocyclic compounds also appear to be affected by electron localization. It is therefore likely that the magnitude of the ortho side-chain coupling constants may be a direct measure of bond order. Long-range coupling data on indole derivatives are reported. In two β,β-dimethylstyrenes the stronger side-chain to ring coupling is to the ortho position. The relation between allylic coupling and electron delocalization is explored and a new criterion for electron delocalization proposed.