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

Abstract

Three-step reactions starting from 2-chlorotropone with dimethylthiobarbituric acid afforded 7,9-dimethylcyclohepta[ b]pyrimido[5,4- d]thiophen-8(7 H),10(9 H)-dionylium tetrafluoroborate 5·BF 4 − , 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 5·BF 4 − . The stability of cation 5 is expressed by the p K R+ value, which was determined spectrophotometrically as 5.1. The electrochemical reduction of 5 exhibited low reduction potential at −0.53 (V vs Ag/AgNO 3), upon cyclic voltammetry (CV). In a search for the reactivity, reactions of 5·BF 4 − 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 5·BF 4 − toward some alcohols under aerobic conditions were carried out to give the corresponding carbonyl compounds in more than 100% yield [based on compound 5·BF 4 − ], suggesting the oxidizing function of 5·BF 4 − toward alcohols in the autorecycling process. The UV–vis and fluorescence spectra of 5 were studied to suggest the electron transfer from alcohols to the excited 5 .