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

Novel areno-annulated 1,3-dimethyl-10-phenylcyclohepta[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dionylium ions 12a,b+·BF4- and 16a+·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 pKR+ values which were determined spectrophotometrically as the values of ca. 0.5−9.0. The pKR+ 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+·BF4- with some nucleophiles, hydride and diethylamine, were carried out. Although the reactions of 12a+·BF4- afforded C11 adduct 19 as a single product, the addition reactions of 12b+·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+·BF4- and 16a+·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.