Study On One-Pot Synthesis Of Dibenzopyranone By Photocatalysis

Dibenzopyranone,also known as benzocoumarin,acts as a ubiquitous motif of many natural products and exhibits various bioactivities and medicinal value.Therefore,the synthesis of dibenzopyranone has become a hot topic in recent researches.In this thesis,dichlorocoumarin(2)can react with 2,3-disubstituted butadiene(3)under the irradiation of an incident ultraviolet light of ?>300 nm to give the dibenzopyranones(1)via 1,6-diradical recombination and rapidly elimination of two hydrogen chloride in of 11%-19%yields.The main products of this reaction are the cyclobutanes(4)in of 55%-74%yields,which can be transformed to dibenzopyranones(1)in high yields through a thermal-photo treatment.The cyclobutanes 4 were absorbed onto silica gel and heated to give the labile hexatriene intermediate via loss of one HCl,which can afford the dibenzopyranones by elimination of another HCl under the irradiation of light.Therefore,the overall yields of 1 can be increased to 62%to 83%.Furthermore,we have integrated these photo-thermal-photo reactions into a novel one-pot approach from 2 and 3 to give dibenzopyranones in 70%-80%overall yields:Dichlorocoumarin(2)and 2,3-disubstituted butadiene(3)were directly irradiated with UV light at ?>300 nm until 2 was completely consumed and then the solvent and excess 3 were removed,the residue was absorbed onto silica gel and heated at 100 ?.The mixture was extracted with chloroform and the resulting solution was irradiated with UV light.The chloroform was removed and the crude product was recrystallized to give 1.This one-pot synthesis of dibenzopyranones using photo-thermal-photo reactions does not require column chromatography to sperate the products,which reduces the difficulty of experimental operation and simplifies the operations.We found that dichlorocoumarin can react with a special diene a-methyl styrene(3c)to give dibenzopyranones by this one-pot protocol.This one-pot methodology provides a new synthesis approach to dibenzopyranones.In the process of synthesis of starting materials,we have found a new synthesis of 3,4-dichlorocoumarin from 4-chlorocoumarin and NCS mediated by copper chloride(CuCl2),then we developed it to a general 3-halogenation for coumarin derivatives.This new method not only reduces the operation difficulty of the experiment,but also improves the synthesis yield of 3-halo coumarin.