Substituted 1,8-naphthyridine complexes of iron(II) and iron(III)

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

“…We then added sulfo-mix, which would presumably drive ring closure, subsequent loss of water, and aromatization during heating; the reaction was then quenched over ice, and worked up to produce a crystalline solid after basification from which we could sublime or recrystallize the dimethyl compound in much improved yield. The literature [3] cites addition of crotonaldehyde to an already formed solution of amine and sulfo-mix at 110°; in our hands this method gave a best yield of 15%, whereas our improved method reliably gave at least 30% of solid, with a work-up which avoided extraction with large volumes of solvents.…”

“…The dimethyl compound was generated from an adaptation of the Skraup synthesis, adapted by Good and coworkers, which we modified to improve the reported yield to ca. 40% [3]. Other syntheses of 2,7-dimethyl-1,8-naphthyridine offering comparable overall yields have also been developed [4,5], although the number of reaction steps, and reaction time, is more than we report here.…”

“…This preparation, presumably that of nitrobenzenesulfonic acid, was adapted from several previous reports [2,3]: in a 1.00 L three-necked flask equipped with a stir bar was charged 30% oleum (230.0 g, 861.6 mmol) and at a steady temperature of 25°w as added nitrobenzene (52.6 g, 427.3 mmol) over a 30 minute period. Stirring was maintained at ca.…”

“…This compound was prepared through modification of an adaptation of the Skraup synthesis, as applied by Good and co-workers, which utilized the "sulfo-mix" reagent [3]. In a 1.00 L three-necked flask equipped with overhead stirrer, in an ice-water bath, crotonaldehyde (41.60 g; 593.5 mmol) was added dropwise to a stirring solution of 2-amino-6-methylpyridine (18.00 g; 166.4 mmol) in water (75 mL).…”

“…The mixture was stirred at room temperature for four hours, then the solvent removed in vacuo to yield a solid yellow paste to which was added water (20 mL) to precipitate an ecru solid; this was allowed to air dry to furnish 0.27 g (70%) of compound 1e. A portion of this solid was recrystallized from acetone to produce large pale-yellow plates; mp 100-102°; ir ( The synthesis of the 2,7-dimethyl-1,8-naphthyridine "synthon" using sulfo-mix was improved in several useful ways: one was the use of 30% oleum in the preparation of sulfo-mix as opposed to 20%, as cited previously [3]. It is found that miscibility of sulfomix with water is reliably achieved within 2 hours with our improvement, whereas the literature method with 20% oleum appeared unpredictable, and could take up to several days.…”