Solvent effect on the reactivity of 1,10-phenanthroline-5,6-dione towards diazomethane

In an aprotic medium, such as THF, Et2O or CH2Cl2, the reaction of 1,10-phenanthroline-5,6-dione with diazomethane gave 5,6-methylenedioxy-1,10-phenanthroline as the only product. In contrast, in a protic solvent, such as 2-propanol or ethanol, the nucleophilic attack of CH2N2 occurred on carbonyl carbons, resulting in the formation of dispiro[5,6-dihydro-1,10-phenanthroline-5,6-dioxirane] as the main product. When the reaction with CH2N2 was carried out in methanol, the only product which could be isolated from the reaction mixture, dimethyl 2,2′-bipyridine-3,3′-dicarboxylate, resulted from a break of the C(5)–C(6) bridge.