Novel synthesis and oxidizing ability of tropylium ions annulated with two 2,4-dimethylfuro[2,3-d]pyrimidine-1(2H),3(4H)-diones.

Convenient preparation of novel tropylium ions annulated with two 2,4-dimethylfuro[2,3-d]pyrimidine-1(2H),3(4H)-diones, 12a(+).BF(4)(-) and 12b(+)().BF(4)(-), consists of a reaction of 2-methoxytropone with dimethylbarbituric acid to give 7,9-dimethyl-3-[1',3'-dimethyl-2'(1'H),4'(3'H),6'(5'H)-trioxopyrimidin-5'-ylidene]cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dione 8 and the following oxidative cyclization by using DDQ or photoirradiation under aerobic conditions. On the basis of the MO calculations, the selectivity of two types of oxidative cyclization reactions of 8 was rationalized. X-ray crystal analyses and MO calculations were carried out to clarify the structural characteristics of 12a(+). BF(4)(-) and 12b(+).BF(4)(-). The stability of cations 12a(+) and 12b(+) is expressed by the pK(R) + values which were determined spectrophotometrically as 8.8 and 8.6. The electrochemical reduction of 12a(+) and 12b(+) exhibited reduction potential at -0.63 and -0.62 (V vs Ag/AgNO(3)), respectively. Reactions of 12a(+)().BF(4)(-) and 12b(+)().BF(4)(-) with some nucleophiles, hydride and diethylamine, were carried out to clarify that the reactivity of 12a(+)().BF(4)(-) and 12b(+).BF(4)(-) was substantially dependent on the annulating position. The oxidizing ability of 12a(+).BF(4)(-) and 12b(+).BF(4)(-) toward alcohols and amines in the autorecycling process was demonstrated as well.