Novel synthesis and properties of 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]thiophen-8(7H),10(9H)-dionylium tetrafluoroborate: autorecycling oxidation of some alcohols under photo-irradiation

Three-step reactions starting from 2-chlorotropone with dimethylthiobarbituric acid afforded 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]thiophen-8(7H),10(9H)-dionylium tetrafluoroborate , which is the isoelectronic compound of the 5-ethyl-3-methyllumiflavinium ion. The X-ray crystal analysis and MO calculation were carried out to clarify the structural characteristics of . The stability of cation is expressed by the pKR+ value, which was determined spectrophotometrically as 5.1. The electrochemical reduction of exhibited low reduction potential at −0.53 (V vs Ag/AgNO3), upon cyclic voltammetry (CV). In a search for the reactivity, reactions of with some nucleophiles, hydride, diethylamine, thiols, and methanol, were carried out, which revealed that the introduction of nucleophiles to give regio-isomers is dependent on the nucleophile. The photo-induced oxidation reactions of toward some alcohols under aerobic conditions were carried out to give the corresponding carbonyl compounds in more than 100% yield [based on compound ], suggesting the oxidizing function of toward alcohols in the autorecycling process. The UV–vis and fluorescence spectra of were studied to suggest the electron transfer from alcohols to the excited .