Study On The New Cyclization Of 4-Hydroxy Coumarins

4-hydroxycoumarin is the basic constituent units within active natural products,and which has been widely used as important starting material in the field of organic synthesis.For example,4-hydroxycoumarin was used for constructing a variety of heterocyclic compounds,biologically active molecules and natural products including anti-HIV,anticancer.Many of the reported literatures indicate that the specific enol isomerism of 4-hydroxycoumarin’s leads to its C-3 position exhibiting more activity than other postions,making it easier to participate in organic transformation reactions.Based on the above understanding,we started a series of studies on the novel organic transformation of 4-hydroxycoumarin and its derivatives by using the complexes of Ag(I)and Rh(III)as catalysts.The main contents are listed as follows:(1)Under the microwave irradiation,we successfully realized the Ag2O-promoted cyclization reaction of 4-hydroxycoumarin with α-carbonyl acid,affording the complex organic molecules with all carbon quaternary center.The results show that the cyclization can tolerate a broad scope of substituents with the formation of the desired target products in good isolated yields,and someone even can be scaled up to gram-scale synthesis.It was found that the cyclization reaction has the characteristics of mild reaction conditions and simple operation,which is distinct from the reported methods for constructing quaternary stereocenter.(2)A series of HIR reagent containing coumarin skeleton was easily prepared from the commercially available 4-hydroxycoumarins as the starting material.By using [Cp*RhCl2]2 as the catalyst and Ag2 O as the additive,the alkynyl carboxylic acid and the HIR reagent underwent the tandem cyclization reaction through decarboxylation to obtain the benzofuran skeleton.The decarboxylative cyclization reaction can occur under mild reaction conditions,generating the target molecucles in good yields and high regioselectivity,and which provides a new path for complex organic molecular synthesis.