Aerobic Oxidative Coupling Of Resveratrol And Its Analogues By Visible Light Using Mpg-C₃N₄as A Bio-inspired Catalyst

Resveratrol and its analogues, which have the bioactivities of anti-microbial,anti-inflammatory, anti-thrombotic and antioxidant, have received increasing attentionin recent years. The studies focus not only on their diverse bioactivities anddevelopment of novel potent analogues for pharmaceutical purposes, but also onexploration of their potential applications as building blocks for construction of morecomplicated oligomers via bio-inspired synthesis. Recently, bio-inspired syntheticstrategies towards these oligomers were studied widely and have become a hotresearch topic. Besides a concise review on the bio-inspired synthesis ofoligostilbenes, visible-light catalysis and the application of heterogeneous catalystmpg-C3N4in organic synthesis, this thesis dealed with the studies on the aerobicoxidative coupling of resveratrol and its analogues by visible light using mpg-C3N4asa bio-inspired catalyst and exploration of the mechanism by a series of experiments.The works are outlined as follows:1. The preparation of resveratrol and its analogues. Fifteen resveratrolanalogues were designed and synthesized via the Witting-Horner reaction, Perkinreaction, McMurry reaction and so on.2. Aerobic oxidative coupling of resveratrol and its analogues by thevisible-light photocatalytic reaction. In this section, by introducing mpg-C3N4asthe bio-inspired catalyst, molecular oxygen, a major source of reactive oxygenspecies (ROS) in vivo, was successfully used as a cheap，environmentally，benignand most readily available oxidant for the oxidative coupling of resveratrol and itsanalogues. Addition of2,6-lutidine could increase the ionization of resveratrol andits analogues and accelerate the generation of the phenolate anion, a muchstronger electron donor. The increasement of phenolate anion could facilitated the single electron transfer (SET) between substrates and valence band of excitedmpg-C3N4or superoxide anion radical. As the result, the bio-inspired synthesis of-viniferin could be achieved with high chemoselectivity.3. The exploration of the photocatalytic mechanism. The stilbenes without4-hydroxy were subjected into the standard condition, and no desired productswere detected, however, trace mount of aldehydes that the cleavage of [2+2]cycloaddition products generated by the reaction of stilbenes with singlet oxygenwere detected by GC-MS. The side reaction was effectively avoided due to thesuppression of the generation singlet of oxygen in our reaction system, Meanwhile，the experiments proved that the4-hydroxy was necessary for the dimeric reaction.The oxidation potential of resveratrol and its analogues measured by cyclicvoltammetry in different pH value were in accord with the experimental facts, thisfurther confirmed the accelerative mechanism that the base decreased theoxidation potentional of the substrates and accelerated the approach of superoxideanion free radical. Addition of5,5-dimethyl-1-pyrroline N-oxide (DMPO), aquencher of superoxide anion radical and phenoxyl radical, to the photocatalyticaerobic oxidative coupling system entirely suppressed the reaction, no-viniferinwas detected, and potassium superoxide was used as another source of superoxideanion instead of the photocatalytic aerobic condition and-viniferin were obtained.The results indicated that the O2generated by photoinduced electron transfer wasthe vital ROS in the initial step of radical coupling pathway. In the heterozygousexperiments, we obtained the products generated by the coupling of two radicalsfrom different sources, the experiments strongly indicated that the reactionperformed through radical-radical coupling pathway.