Investigation of the reaction of 2- (2-aminophenyl)furan with maleic anhydride

Abstract

Phenanthridinone derivatives have long been used as anticancer, antileukemic, antitumor, antiviral, antimicrobial, antifungal, antimalarial, and anti-irritant drugs. Despite several methods for the synthesis of phenanthridinone derivatives, flexible and versatile methodologies to construct phenanthridinones are still desirable. An intramolecular Diels-Alder reaction was used to construct the phenanthridine skeleton. The starting material was 2-(2-aminophenyl)furan. 2-(2-Аminophenyl)furan was obtained by arylation of furan with 2-nitrophenyldiazonium chloride followed by reduction of the nitro group with sodium borohydride in the presence of nickel chloride hexahydrate. The amine was acylated with maleic anhydride in benzene at room temperature. The formation of the Diels-Alder reaction adduct occurs when maleinimide 2-(2-aminophenyl) furan is heated in dioxane. During heating, the oxacycloheptene moiety is cleaved. And as a result, the oxabicycloheptene fragment is flavored to form 6-hydroxyphenanthridine-7-carboxylic acid. This reaction is confirmed by chromato-mass spectrometry. It is also interesting that when maleinimide 2-(2-aminophenyl) furan is heated in benzene it's leads to the formation of dark-colored resinous products.It is known that such intramolecular cycloadditions involving the furan ring occur with the formation of exo-adducts of the Diels-Alder reaction. In our opinion, the cis-placement of the carboxyl group and the bridging oxygen atom promotes easy proton migration with the opening of oxabicycloheptene. It should also be noted that in solution the Diels-Alder reaction product is in phenanthridinone tautomeric form. Proof of this is the signal of the hydrogen atom of the hydroxy group at 12.83 ppm and NH group proton at 11.76 ppm in the H 1 NMR spectrum of the obtained compound. Keywords: furan derivatives, 2-arylfurans, tandem cyclizations, phenanthridines