Five-membered 2,3-dioxo heterocycles: LXXII. Recyclization of isopropyl 2-(1-aryl-4,5-dioxo-2-phenyl-4,5-dihydro-1H-pyrrol-3-yl)-2-oxoacetates by the action of aliphatic amines

Abstract

Reactions of isopropyl 2-(1-aryl-4,5-dioxo-2-phenyl-4,5-dihydro-1H-pyrrol-3-yl)-2-oxoacetates with alkylamines involve pyrroledione-pyrroledione recyclization with formation of isopropyl 1-aryl-2-hydroxy-4,5-dioxo-3-[phenyl(alkylamino)methylidene]pyrrolidine-2-carboxylates. * For communication LXXI, see [1].Methyl 1-aryl-3-aroyl-4,5-dioxo-4,5-dihydro-1H-pyrrole-2-carboxylates are known to take up aromatic amines at the carbon atom in position 2 of the pyrrole ring to give substituted 5-arylamino-3-hydroxy-1H-pyrrol-2(5H)-ones [2,3]. Reactions of isopropyl 2-(1-aryl-4,5-dioxo-2-phenyl-4,5-dihydro-1H-pyrrol-3-yl)-2-oxoacetates with aromatic amines involve initial nucleophile addition at the carbon atom in position 2 or 5, followed by opening of the pyrrole ring at the N 1 -C 2 or N 1 -C 5 bond and intramolecular cyclization to isopropyl 1-aryl-2-hydroxy-4,5-dioxo-3-[phenyl(arylamino)methylidene]pyrrolidine-2-carboxylates [4-6]. Reactions of 4-acyl-substituted 1H-pyrrole-2,3-diones with aliphatic amines were not studied previously.In continuation of our studies on nucleophilic recyclizations of monocyclic 1H-pyrrole-2,3-diones, in the present work we examined reactions of isopropyl 2-(1-aryl-4,5-dioxo-2-phenyl-4,5-dihydro-1H-pyrrol-3-yl)-2-oxoacetates Ia-Id with primary alkylamines IIaIId. The reactions were carried out using equimolar amounts of the reactants in anhydrous chloroform at room temperature; the reaction time was 8-10 h, and the products were the corresponding isopropyl 1-aryl-2-hydroxy-4,5-dioxo-3-[phenyl(alkylamino)methylidene]pyrrolidine-2-carboxylates IIIa-IIIh in good yields (Scheme 1).Compounds IIIa-IIIh were isolated as bright yellow or orange high-melting crystalline substances which are readily soluble in dimethyl sulfoxide, dimethylformamide, and other organic solvents (except for saturated hydrocarbons) and insoluble in water. The IR spectra of IIIa-IIIh contained absorption bands due to stretching vibrations of OH and NH groups (a broad band in the region 3198-3334 cm -1 ), lactam carbonyl group (C 5 =O, 1727-1760 cm -1 ), ester carbonyl group (1713-1734 cm -1 ), and exocyclic ketone carbonyl group participating in intramolecular hydrogen bond (a broad band in the region 1605-1634 cm -1 ).Compounds IIIa-IIIh displayed in the 1 H NMR spectra signals from protons in the aromatic rings, substituents attached thereto, and alkyl groups on the exocyclic nitrogen atom, two doublets from methyl protons in the isopropyl group (δ 0.72-0.81 and 0.74-0.90 ppm), a multiplet from the CH proton in the isopropyl group (δ 4.37-4.43 ppm), and a broadened doublet from the NH proton (δ 11.38-12.35 ppm) in IIIc and IIId or a triplet at δ 11.12-11.55 ppm (IIIa, IIIb, IIIe-IIIh). The OH proton signal was obscured by those of aromatic protons. The following signals were present in the 13 C NMR spectrum of compound IIId,