Synthesis, Properties, and Oxidizing Ability of 9,11-Dimethylbenzocyclohepta[6,7-<i>b</i>]pyrimido[5,4-<i>d</i>]furan- 10(9<i>H</i>),12(11<i>H</i>)-dionylium Tetrafluoroborate

Convenient preparation of novel 9,11-dimethylbenzocyclohepta[6,7-b]pyrimido[5,4-d]furan-10(9H),12(11H)-dionylium tetrafluoroborate 11·BF4- consisted of a condensation reaction of benzo[d]tropone with dimethylbarbituric acid and following oxidative cyclization reaction by using DDQ-Sc(OTf)3 or photoirradiation under aerobic conditions. Alternative synthesis of 11·BF4- was also accomplished by a condensation reaction of 2-methoxybenzo[d]tropone with dimethylbarbituric acid and a subsequent cyclization reaction by using 42% aq HBF4. The X-ray crystal analysis and MO calculation were carried out to clarify the structural characteristics. Properties of the cation 11 were studied by the pKR+ value (4.7) and reduction potentials (−0.46 and −1.07 V vs Ag/AgNO3) as well as the reaction with some nucleophiles. The oxidizing ability of 11·BF4- toward alcohols in the autorecycling process was demonstrated as well.