Elaboration of 1,8‐naphthyridine‐2,7‐dicarboxaldehyde into novel 2,7‐dimethylimine derivatives

Abstract

The known 1,8-naphthyridine-2,7-dicarboxaldehyde was prepared by SeO 2 oxidation of 2,7-dimethyl-1,8-naphthyridine. The dimethylated naphthyridine molecule was assembled from an adaptation of the Skraup synthesis using 2-amino-6-methylpyridine and crotonaldehyde to afford a reproducible 37% yield, and constitute a significant advance over the literature of this reaction. The condensation of 1,8-naphthyridine-2,7-dicarboxaldehyde with various primary amines (R = -C 6 H 11 , -CH 2 C 6 H 5 , -C(CH 3 ) 3 , -C 10 H 15 , and CH 2 CH 2 SCH 2 CH 3 ) in alcohol affords diimines 1(a-e). The inherent crystallinity of 1(a-e) affords pure compounds in reasonable to excellent yields (ca. 70%) after evaporation of solvent and recrystallization. The anticipated spectroscopic features of (N=C-H) 1 H nmr shift and ν(C=N) in the ir spectrum appear around 8.50 δ and 1640 cm -1 , respectively, for the series 1(a-e). These novel naphthyridines typically display the signature 1 H nmr doublets at ca. 8.15-8.30 δ ascribed to the 3 and 4 naphthyridine protons, consistent with a mirror plane (through the quaternary carbons) perpendicular to the naphthyridine plane, and syn, syn relationships of the naphthyridine moiety with each imine nitrogen lone pair. Complexation studies of 1(a-e) with transition metals of biological relevance such as copper(I) and copper(II) will be reported elsewhere.

A Novel Ruthenium(II) Polypyridyl Complex Bearing 1,8-Naphthyridine as a High Selectivity and Sensitivity Fluorescent Chemosensor for Cu2+ and Fe3+ Ions

“…All the solvents and reagents (analytical grade and spectroscopic grade) were purchased from reagent companies and used without further purification. 2,7-Dimethly-1,8-naphthyridine [37,38] and cis -Ru(bpy) 2 Cl 2 ·2H 2 O [39] were obtained according to the literature procedures.…”

Complexation of Tetrakis(acetato)chloridodiruthenium with Naphthyridine‐2,7‐dicarboxylate – Characterization and Catalytic Activity

“…Infrared spectra were recorded with samples as KBr pallets. The ligand dcnpH 2 , [10] dicarbonyl{(P,PЈ,N-1,9-diphenyl-2,3,4,5,6,7,8,9-octahydro-1H-5,1,9-benzazadiphosphacycloundecine)}chlororuthenium (4), [13] (N,O-2-pyridinecarboxylato)(η 6 -p-cymene)chlororuthenium (5), [14] and (N,N-bipyridine)(η 6 -benzene)chlororuthenium chloride (6) [15] were prepared according to the reported methods. Cyclic voltammetry measurements were performed with a CH instruments 750A potentiostat with a graphite working electrode and Pt wire auxiliary electrode at ambient temperature.…”

“…[10] The deprotonation of 2 with Ca(OH) 2 was performed at ambient temperature in aqueous medium for 12 h. The treatment of the calcium salt with Ru 2 (OAc) 4 Cl in air resulted in the formation of deep purple crystalline solid 3. The synthetic procedure for 3 is different from that for 1 (Scheme 1).…”

Practical Synthesis of 1,8-Naphthyridine-2,7-dialdehydes Syntone

“…Several authors obtained dialdehyde III by oxidation of corresponding dimethyl precursors IV with SeO2 (eqn. 1) [3][4][5][6][7][8][9]. Hence, compound IV could be the key intermediate in synthesis of dialdehyde III.…”

“…However, an attempt is made for synthesis of compound IV (Skroup synthesis) according to Fox et al [6] using pyridine and crotonaldehyde gave substantial amount of black sticky gum which was very difficult to separate from the desired naphthyridine (eqn 6).…”