Synthesis of 1H-Pyrazolo[3,4-b]quinoxaline Derivatives by Modification of the Regiospecific Reaction - the Influence of the Microwave Field

The microwave-assisted reductive cyclization reaction with the use of triphenylphosphine as a reducing agent in the synthesis of 1H-pyrazolo[3,4-b]quinoxaline derivatives was investigated. Contrary to the conventional method of conducting the reaction, the process in the reactor takes 25 minutes with moderate yields (30-38 %). This procedure was used to obtain three new 1,3-dimethyl-1H-pyrazolo[3,4-b]quinoxaline derivatives with substituents at position 6 of different donor-acceptor character, which were used to determine the basic photophysical properties (UV-Vis absorption spectra, fluorescence emission spectra) and the quantum yields of fluorescence were appointed. The measurement results indicate the possible use of new compounds as materials for OLEDs. The conducted research brings new knowledge in the field of 1H-pyrazolo[3,4-b]quinoxaline derivative systems and provides an alternative to conventional synthesis of pyrazoloquinoxalines.