Synthesis and applications of fused N- and O-heterocyclic systems from nitrodienic building-blocks

N-containing and O-containing heterocycles are widely distributed in natural products essential for life and are often responsible for the pharmaceutical activity of a lot of drugs and lead-compounds. Exploiting the electrophilic nature of functionalized nitrodienic building-blocks, combined with an opportune nuclophile, new protocols for the synthesis of fused N- and O-heterocycles, has been developed. When using 2-aminopyridines or pyrrole as nucleophiles in the reaction with a suitable nitrodienic building block, it is possible to obtain imidazo[1,2-a]pyridines and 7-aryl-6-nitroindoles respectively. The particular substitution of these N-heterocycles was exploited to obtain fused heteropolycles systems: starting from imidazo[1,2-a]pyridines, through a photoinduced 6π-electrocyclization, new fused fluorescent polycycles were synthetized, and their fluorescent properties have been analysed, while performing a classical Cadogan reaction on 7-aryl-6-nitroindoles lead to functionalized pyrrolo[3,2-c]carbazoles. Pyrrolo[3,2-c]carbazoles can react with nitrosoalkenes, leading to the products of alkylation, and this reaction has been studied in collaboration with the Organic Chemistry Group of the University of Coimbra. Since the green approach in organic chemistry is gaining more and more importance, the possibility to use heterogeneous catalysis of Graphene Oxide (GO) in the synthesis of heterocycles, starting from nitrovinylic moieties, has also been investigated. Finally, from the reaction between some particular nitrostilbenes and 2-naphthtol or 8-hydroxyquinoline, it was possible to synthetize a small library of dihydronaphtho- and naphthofuran derivatives. Naphthofurans obtained shown a good fluorescence, and their nature of diarylethenes made them promising substrates for a 6π-electrocyclization, with further expansion of the aromatic system, and the formation of a new benzenic ring, leading to new fused O-heterocyclic systems.