The Aerobic Aromatization And Difluorination Of Arene Via Visible-Light Photoredox Catalysis

Visible-light photoredox catalysis, which shows excellent functional group tolerance, high chemical selectivities and typical features of green chemistry, has been provided to be a new and powerful tool for promoting chemical transformations. Especially, the organocatalytic aerobic oxidation and directed functionalization of arenes and heteroarenes via visible-light photoredox catalysis greatly meet the increasing demand for green and sustainable chemistry. In this thesis, several new visible-light driven photocatalytic systems aimed to green and sustainable chemistry were developed and applied to aerobic oxidation and difluorination. The results were obtained as following:1. Visible-light driven aerobic oxidation of various phenolic imines, dihydropyrimidines and dihydropyridines have been achieved with good to excellent yields under irradiation of 3 W blue LEDs light by using 1 mol% organic dye TBA-eosin Y as photocatalyst and molecular oxygen as oxidant. Mechanistic studies indicate addition of a base significantly contributes to the electron transfer from substrates to the excited TBA-eosinY, and thereby suppressing the side reaction of singlet oxygen and results in a highly chemoselective oxidation.2. The directed difluoroacetamidation and difluoromethylenephosphonation of unactivated arenes and heteroarenes with commercially available bromodifluoro-acetamides and diethyl bromodifluoromethyl phosphonate via visible-light photoredox catalysis has been efficiently achieved at room temperature. Using fac-Ir(ppy)3 as a photosensitizer and a 3W blue LED as a light source, an array of aromatic compounds containing difluoroacetamides difluoromethylenephosphonates were prepared directly from the corresponding arenes and heteroarenes in excellent to moderate yields. Additionally, the reaction mechanism was studied by photoluminescence quenching, spin-trapping, and kinetic isotope effect experiments. The results show that the addition of a difluoromethyl radical to the aromatic ring is responsible for the a successful photocatalytic difluoromethylation.