Application Of Claisen-schmidt Reaction In Diversity-oriented Synthesis And Dual-channel ESIPT Fluorescent Probe

Green chemistry has become one of the frontier disciplines of international chemical research.Diversity-oriented synthesis（DOS）are often used to discover and construct various molecular frameworks and increase molecular libraries.DOS has made great achievements in the synthesis and screening of natural products and drugs,which meets the requirements of green chemistry.The Claisen-Schmidt aldol condensation reaction is a classic reaction to formα,β-unsaturated aldehydes or ketones,and is widely used in green synthetic chemistry.The cyano group may not only hydrolyze to form amides or carboxylic acids,but also interact with the negatively charged adjacent O atom to achieve an in situ intramolecular addition reaction and rearrangement,and is widely used to synthesize various important N-containing compounds.Flavonoids have excellent physiological activity,low toxic and side effects.The flavonoid molecule has excellent optical properties due to the presence of excited state intramolecular proton transfer（ESIPT）,such as large Stokes shift,dual-wavelength fluorescence emission,etc.In recent years,it has been developed as a fluorophore for fluorescent probes.Fluorescent probe molecules with dual-channel ESIPT are susceptible to environmental influences.When the environmental conditions change,the dominant structure present in the system can change accordingly,so as to specifically recognize different detection substances.However,there are few studies on fluorescent probes with du al-channel ESIPT properties.In this paper,seven different heterocyclic compounds were synthesized in DOS based on the Claisen-Schmidt reaction.In addition,the synthesized pyridoflavonoid ligands with dual-channel ESIPT can detect different metal ions a nd lanthanides under different p H conditions to achieve green detection.Precursors of four kinds of dual-channel ESIPT pyridoflavonoid derivatives and H ₂O₂ fluorescent probes were synthesized.The full text is divided into four parts to elaborate.The first part describes the research progress of Claisen-Schmidt condensation reaction,diversity-oriented synthesis and design mechanism of fluorescent probe in detail,and proposes the research basis of this topic.In the second part,seven heterocyclic compo unds were synthesized in DOS by Claisen-Schmidt condensation amphiphilic intermediates,such as isoindolinone compounds 4,5,6;flavonoid compounds 7,8,10;benzofuranone compound 9.The compounds were fully characterized by ¹H NMR,¹³C NMR,HRMS,IR and X-ray single crystal diffraction techniques.The Gaussian 09 B3LYP method was used to calculate the frontier molecular orbits under different conditions,and the relationship between HOMO properties and reaction orientation was analyzed.The third part is to synthesize pyridoflavonoid ligands 13 with dual-channel ESIPT properties,and study the UV-Vis absorption spectrum and fluorescence emission spectrum of the ligands under different p H conditions.UV-Vis absorption spectrum shows that under acidic conditions,the maximum absorption wavelength of the compound does not shift,but under alkaline conditions,the hydroxyl is deprotonated,the conjugated effect of the hydroxyl oxygen atom with the adjacent carbon is enhanced,causing the maximum absorption pea k of the compound red shift.Fluorescence emission spectroscopy shows that the hydrogen bond isomers present in the system are distinct under different p H conditions,which makes the position of the emission peak change.Under strongly acidic conditions,t he emission peak is red-shifted to about 550 nm,and under alkaline conditions,the red-shifted peak is about 523 nm.In addition,the detection of different metal ions and lanthanides by pyridoflavonoid ligands under different p H conditions was further st udied.The results show that Mg²⁺,Cu²⁺,Zn²⁺,La³⁺,Yb³⁺can be detected at different p H values.In the fourth part,four kinds of dual-channel ESIPT fluorescent probe precursors and a fluorescent probe molecule were synthesized and characterized by ¹H NMR spectroscopy and ¹³C NMR spectroscopy.The detection of H₂O₂ by fluorescent probe molecules was studied,but the recognition selectivity and sensitivity under this detection condition are poor.