Synthesis of new heterocyclic enamines and their cyclization with oxalyl chloride

Abstract

Substituted furan-2,3-diones are convenient synthons exhibiting high reactivity and unusual chemical behavior toward various reagents [1, 2]. Heterocyclic ensembles derived from these compounds were found to possess versatile biological activity [3]. Functionally substituted furan-2,3-diones can be synthesized by reaction of heterocyclic β-enaminoketones with oxalyl chloride [4–6]. By reaction of diaroylacetylenes Ia and Ib with biphenyl-3,3′,4,4′-tetraamine (II) according to the procedure described in [7] we obtained new heterocyclic enamines, 2,2′-(3,3′-diaryl-1,1′,2,2′-tetrahydro-6,6′-biquinoxaline-2,2′-diylidene)bis(1-arylethanones) IIIa and IIIb (Scheme 1). Heating of compounds IIIa and IIIb with oxalyl chloride in boiling anhydrous chloroform led to the formation of new representatives of the furan-2,3-dione series, 4,4′-(3,3′-diaryl-6,6′-biquinoxaline-2,2′-diyl)bis(5-aryl-2,3-dihydrofuran-2,3-diones) IVa and IVb (Scheme 2). Presumably, bis-furandiones IVa and IVb are formed via initial acylation of compounds IIIa and IIIb with oxalyl chloride at the exocyclic =CH fragments to give intermediate acyl chlorides [8] which are converted into hydroxyenimine structure with subsequent intramolecular cyclization. 2,2′-(3,3′-Diphenyl-1,1′,2,2′-tetrahydro-6,6′-biquinoxaline-2,2′-diylidene)bis(1-phenylethanone) (IIIa). A solution of 4.68 g (20 mmol) of compound Ia in 10 ml of acetonitrile was added to a solution of 2.14 g (10 mmol) of tetraamine II in 20 ml of acetonitrile, and the mixture was heated to the boiling point and cooled. The precipitate was filtered off and recrystallized from acetonitrile. Yield 5.75 g (89%), orange– red crystals, mp 252–254°C (from acetone). IR spectrum, ν, cm: 3034 br (NH), 1580 br (C=O). H NMR spectrum, δ, ppm: 6.29 s (2H, CH), 6.93–7.90 m (26H, Harom), 15.70 s (2H, NH). Found, %: C 81.74; H 4.60; N 8.67. C44H30N4O2. Calculated, %: C 81.71; H 4.68; N 8.66. 2,2′-[3,3′-Bis(4-methylphenyl)-1,1′,2,2′-tetrahydro-6,6′-biquinoxaline-2,2′-diylidene]bis[1-(4-methylphenyl)ethanone] (IIIb) was synthesized in a similar way. Yield 5.98 g (85%), orange–red crystals, mp 223–225°C (from acetone). IR spectrum, ν, cm: 3024 br (NH), 1586 br (C=O). H NMR spectrum, δ, ppm: 2.34 s (6H, Me), 2.50 s (6H, Me), 6.35 s (2H, CH), 6.90–7.92 m (22H, Harom), 15.76 s (2H, NH). Found, %: C 82.09; H 5.43; N 7.95. C48H38N4O2. Calculated, %: C 82.03; H 5.45; N 7.97. 4,4′-(3,3′-Diphenyl-6,6′-biquinoxaline-2,2′-diyl)bis(5-phenyl-2,3-dihydrofuran-2,3-dione) (IVa). Oxalyl chloride, 2.52 g (20 mmol), was added to a solution of 6.47 g (10 mmol) of compound IIIa in 40 ml of anhydrous chloroform. The mixture was heated for