Pericyclic [4+2] and [3+2] Cycloaddition Reactions of Nitroarenes in Heterocyclic Synthesis

A summary is given of our results and literature data on the use of nitroarenes in pericyclic [4+2] and [3+2] cycloaddition reactions to give heterocycles fused with the original aromatic carbocycle. Highly electrophilic bicyclic nitroarenes, which are considered superelectrophiles, are capable of undergoing the Diels–Alder reaction with nucleophilic alkenes as C=C–N(O)=O heterodienes to give dihydro-1,2-oxazine N-oxides. Dinitrobenzenes, 1,3,5-trinitrobenzene, and their substituted derivatives and analogs as well as nitrobenzenes and 1,3-dinitrobenzenes fused with electron-withdrawing azoles and pyridine are capable of undergoing 1,3-dipolar cycloaddition as dipolarophiles at the C=C(NO2) bond with N-alkylazomethine ylides serving as 1,3-dipoles to give N-alkylpyrrolidines, pyrrolines, or pyrroles fused to an aromatic ring, depending on the structure of the nitro compound substrates. A relationship was found between the reactivity of the nitroarenes in pericyclic [4+2] and [3+2] cycloaddition reactions and the electrophilicity of these substrates.