1,3-Dipole 1,3-dicarbonyl compound 1,4-dihydropyridines 1-methyl-2-quinolone 8-nitro-5-RO-indolizines C–H functionalization Diels-Alder reaction ICT character PDE4 inhibitors Phenacylation of beta-nitropyridin-2-ones SNAr substitution anchimeric assistance aromaticity conjugate addition cycloaddition dearomatization dihydrofuran direct functionalization electron-withdrawing ability electrophilicity enolate epimerization hexapyrrolohexaazacoronene isoxazoline N-oxide isoxazolo[4,3-b]pyridines nitration nitro nitro group nitroketone nitronate