Synthesis, properties, and oxidizing function of 6-substituted 7,9-dimethylcyclohepta[ b]pyrimido[5,4- d]pyrrole-8(7 H),10(9 H)-dionylium tetrafluoroborates

Abstract

Uracil-annulated heteroazulenes, 6-substituted 7,9-dimethylcyclohepta[ b]pyrimido[5,4- d]pyrrole-8(7 H),10(9 H)-dionylium tetrafluoroborates 7a, b·BF 4 − , which are the isoelectronic compounds of 5-dezazaflavin, were synthesized. X-Ray crystal analysis and MO calculations were carried out to clarify the structural characteristics of 7a, b·BF 4 − . The stability of cations 7a, b is expressed by the p K R+ values which were determined spectrophotometrically to be 10.9 and 11.2, respectively. The electrochemical reduction of 7a, b exhibited high reduction potentials at −0.84 and −0.87 (V vs Ag/AgNO 3) upon cyclic voltammetry (CV). A good linear correlation between the p K R+ values and reduction potentials ( E1 red) of 7a, b·BF 4 − and reference compounds 4·BF 4 − and 5·BF 4 − was obtained. In a search of the reactivity, reactions of 7a, b·BF 4 − with some nucleophiles, hydride and diethylamine, were carried out to clarify that the introduction of nucleophiles to give regio-isomers is dependent on the nucleophile. The photo-induced oxidation reactions of 7a, b·BF 4 − toward some alcohols under aerobic conditions were carried out to give the corresponding carbonyl compounds in more than 100% yield [based on compounds 7a, b·BF 4 − ], suggesting the oxidizing function of 7a, b·BF 4 − toward alcohols in the autorecycling process.