Tandem Synthesis Of Pyranocoumarin Derivatives

Developing new synthetic method to get bioactive compounds is one of the most attractive areas in organic chemistry.In this thesis,two new methods to synthesize pyranocoumarin derivatives are explored from easily available starting materials.The results are summarized below:1.DDQ-promoted tandem synthesis of pyranocoumarin derivatives via double oxidative C-H activation has been developed.The starting materials of this reaction is 4-hydroxycoumarin and diarylallylic compounds.This efficient approach to functionalized pyranocoumarin proceeds in a single flask via direct C-C bond formation followed by C-O bond formation promoted by DDQ.We also designed an intramolecular reaction oxidized by DDQ,which gives insight into the mechanism,to demonstrate the C-O bond formation is also promoted by DDQ.Radical allylic carbocation is generated during the reaction proceeding,which leads to the formation of two isomer products.The staring materials of the reaction are easily available and the operation of this method is simple.It is also a metal-free catalyzed reaction,which is environmental friendly.2.Lewis acid catalyzed reaction of 4-hydroxycoumarin derivatives with chalcones is developed.It is a new synthetic method to get functionalized pyranocoumarin in a single flask.A plausible mechanism of this reaction is following process.BF₃·Et₂O catalyzes a 1,4-conjugated addition of 4-Hydroxycoumarin toα,β-unsaturated ketones,then generating an addition intermediate.Again,the BF₃ group coordinates to the carbonyl group of the intermediate,and then the ring closure product is formed via an intramolecular nucleophilic attack of hydroxyl group to carbonyl group.The synthetic method can proceed in mild condition with simple operation.