NOVEL ONE-POT SYNTHESIS OF DIHYDROACENAPHTHO[1,2⁢-f⁢][1,3]-OXAZEPINES ⁢VIA⁢ 1,4-DIPOLAR CYCLOADDITION REACTION

A facile three-component reaction involving 3-alkyl(aryl)imidazo[1,5-a]pyridines 7a-g, dimethyl acetylenedicarboxylate 2 (DMAD) and acenaphthene-1,2-dione 5 led to the construction of the respective dihydroacenaphtho[1,2-f][1,3]oxazepine-10,11-dicarboxylates 10a-g in fair yields. Structures of the latter tetracyclic adducts, are based on NMR and MS spectral data and confirmed by single-crystal X-ray diffraction analysis for compound 10a. Most logically, the reaction proceeds via initial formation of the relevant diastereomeric spiro[1,3]oxazine-1,4-dipolar cycloadducts 12, 13 which then suffer skeletal rearrangement leading to the respective acenaphtho[1,2-f][1,3]oxazepines 10a-g.