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

Novel areno-annulated 1,3-dimethyl-10-phenylcyclohepta[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dionylium ions 12a,b(+.)BF(4)(-) and 16(a+.)BF(4)(-) 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 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/AgNO(3)) 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(+.)BF(4)(-) with some nucleophiles, hydride and diethylamine, were carried out. Although the reactions of 12a(+.)BF(4)(-) afforded C I I adduct 19 as a single product, the addition reactions of 12b(+.)BF(4)(-) 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(+.)BF(4)(-) and 16a(+.)BF(4)(-) 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.