Study On The Synthesis Of Aromatic Phosphonates/phosphorylated Hydrazines Using Organic Dye As Photocatalyst

Phosphonates are significant structural motifs existing in a large variety of pharmaceutically active molecules,organic materials and agrochemicals.Phosphonates have also been widely used as ligands and synthetic intermediates.The main conventional methods published from 1981 to present for the synthesis of arylphosphonates were the transition-metal-catalyzed cross-coupling of aryl halides with trialkylphosphites or H-phosphonate,pioneered by the work of Hirao et al published in 1981,known as the Hirao cross-coupling.Despite significant achievements,from an environmentally friendly point of view,those procedures still suffer from some drawbacks,such as the use of metals even highly toxic noble metals as catalysts,inconveniently long reaction time as well as high reaction temperature.The use of visible light as an inexpensive and nonpolluting means to initiate organic transformations is especially attractive for developing new and eco-friendly synthetic methodologies.However,only over the past ten years,a fast development of visible light photoredox catalysis for organic synthesis has been witnessed.The visible-light photoredox catalysts developed in recent years include ruthenium and iridium polypyridyl complexes and organic dyes.In spite of the excellent photocatalytic properties of ruthenium and iridium polypyridyl complexes for some organic transformations,the metal complexes are usually expensive and even potential toxic.In contrast,organic dye is a highly attractive alternative to the transition metal complexes in photoredox catalysis in that they are usually less expensive,less toxic,and easier to handle.The recent developed synthetic methodologies towards arylphosphonates were using ruthenium polypyridyl complexes as visible-light photoredox catalysts.Nevertheless,as known from above,the high cost and multi-step synthesis of the noble metal-based photocatalysts and the transition-metal contamination issue might limit their applications,from an environmentally friendly point of view.Based on the research background,we would like to present our newly developed visible-light-driven organic-dye-catalyzed photoredox reaction for the synthesis of arylphosphonates as shown below.This is the first example for the construction of arylphosphonates from arylhydrazines by a dye-catalyzed photocatalytic process under irradiation of visible-light and metal-free reaction conditions.Besides,phosphorylated hydrazides can also be synthesized using the catalytic system.More importantly,a gram-scale experiment can be successfully carried out by using solar light as a renewable and clean energy source.The remarkable features of our work including:?1?visible-light or sunlight as an inexpensive and nonpolluting energy source;?2?The inexpensive and nontoxic organic dye eosin B as photocatalyst.?3?Metal-free and mild reaction conditions.?4?Open air reaction condition and a simple one-pot operation.?5?High feasibility by utilizing sunlight as an illumination source product for gram-scale synthesis.The main content of my thesis:1.Firstly,we chose phenyl hydrazine and triethyl phosphite as model substrates to screen the optimal reaction conditions.Photocatalysts and bases,oxidants,solvents,light sources,temperature,reaction time and the amount of photocatalysts and bases were screened.The optimized condition toward diethyl phenylphosphonates?3a?was established as the following:phenyl hydrazines?0.5 mmol?,triethyl phosphite?1.0 mmol?,organic dye Eosin B as photocatalyst?5 mol%?and DABCO?50 mol%?dissolved in CH₃CN?1.5 mL? with air as oxidant under the irradiation of white LEDs for 6 h.2.Under the optimized reaction condition,we further explore the scope of reaction.22 arylphosphonates were obtained and the highest yield was 74%.Their structures were elucidated by ¹H NMR,¹³C NMR,³¹P NMR and HRMS.3.Then phenyl hydrazine and diphenyl phosphorous oxygen were used as model substrates to screen the reaction conditions.Photocatalysts and base,solvent,temperature,reaction time and light source were investigated.The optimized reaction condition toward phosphinic hydrazide?6a?was established as the following:phenyl hydrazine?0.55 mmol?,diphenyl phosphorous oxygen?0.5 mmol?,Rose Bengal?10 mol%?and Cs₂CO₃ dissolved in CH₃CN?1.5 mL? under the irradiation of white LEDs for 9 h.4.Under the optimized reaction condition,we further explore the reaction scope.Then 10 phosphorylated hydrazides were prepared under the optimized reaction condition.Their structures were elucidated by ¹H NMR,¹³C NMR,³¹P NMR and HRMS.5.Finally,the two mechanisms were proposed based on a serious of control experiments.In summary,we developed novel catalytic system for the synthesis of aryl phosphonates and phosphorylated hydrazides under mild conditions with visible light or sunlight as light source,organic dye as photocatalyst and air as oxidant.