Synthesis, Properties, and Oxidizing Ability of Areno-Annulated 1,3-Dimethyl-10-phenylcyclohepta[4,5]pyrrolo[2,3-d]pyrimidine- 2,4(1,3H)-dionylium Ions

Abstract

[structures: see text] Novel areno-annulated 1,3-dimethyl-10-phenylcyclohepta[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dionylium ions 12a,b+ x BF4(-) and 16a+ x BF4(-) were synthesized by three-step reactions, starting from the reactions of benzo[b]tropone and naphtho[2,3-d]tropone with 6-anilino-1,3-dimethyluracil. Structural characteristics of 12a,b+ and 16a+ were clarified on inspection of the UV-vis and NMR spectral data as well as by X-ray crystal analyses. The stability of cations 12a,b+ and 16a+ is expressed by the pK(R+) values which were determined spectrophotometrically as the values of ca. 0.5-9.0. The pK(R+) value of the naphtho[b]tropylium ion 4+ was clarified to be much lower, at <0. The electrochemical reduction of 12a,b+ and 16a+ exhibited reduction potentials at -0.46 to -0.67 (V vs Ag/AgNO3) upon cyclic voltammetry (CV). The reduction potentials of the benzotropylium ion and cation 4+ were -0.26 and -0.09 V, respectively. In a search for reactivity, reactions of 12a,b+ x BF4(-) with some nucleophiles, hydride and diethylamine, were carried out. Although the reactions of 12a+ x BF4(-) afforded C11 adduct 19 as a single product, the addition reactions of 12b+ x BF4(-) proceeded at both C9 and C11. The attempted reduction of methyl benzoylformate by using 21 was carried out unsuccessfully. The photoinduced oxidation reaction of 12a,b+ x BF4(-) and 16a+ x BF4(-) toward some amines under aerobic conditions was carried out to give the corresponding imines (isolated by converting to the corresponding 2,4-dinitrophenylhydrazones) with the recycling number of 3.6-21.7.