An Efficient Light On-off One-pot Method For The Synthesis Of 3-styryl Coumarins From Aryl Alkynoates

Coumarins as one of common motifs have been extensively investigated due to their biological activities and outstanding optical properties.They are widely applied in pharmaceutical synthesis and photoelectric materials.Therefore,the development of simple,efficient and direct strategies to access coumarins is still desirable in synthetic chemistry.In this thesis,an efficient stepwise one-pot system is demostrated to construct 3-styryl coumarins from alkynotes via both photocatalysis and thermocatalysis processes.The main research contents are as follows:1.An efficient one-pot cascade method to synthesize 3-styryl-4-arylcoumarins from aryl alkynoates is presented.After the screening of catalysts,bases,temperature and reaction time,the optimized conditions were required the combination of visible-light-induced cyclization and Pd-catalyzed Heck reaction.The catalytic system showed broad functional group tolerance and high stereoselectivity.A series of(E)-3-styryl coumarins were obtained in moderate to high yields(Scheme 1).Scheme 12.Based on the above experimental results and the previous reports,a possible mechanism for this one-pot stepwise cascade synthesis is proposed.The results of mechanism study indicate that this synthetic method might be involved the light-driven radical cyclization and palladium-catalysed cross-coupling processes.3-Bromocoumarin is the critical intermediate between the two steps.3.The photoluminescence properties of the synthesized 3-styryl-4-arylcoumarins were investigated.The UV/vis absorption spectrum and fluorescence emission spectrum of the target products as well as fluorescence quantum yields(ΦF)were tested.The results of X-ray analysis and spectroscopic experiments prove that the substituent effect has a significant influence on the spectral properties of the synthesized 3-styryl coumarins.