Coumarins are natural compounds with wide application in organic synthesis as acceptors in different organic reactions with nucleophilic reagents and dienophiles in Diels-Alder reactions as well in reactions of [2+2] or [2+3] cycloaddition and as intermediates in the synthesis of products of practical interest. On the other hand, especially important are their antimicrobial, antiviral, anticancer, enzyme inhibition, anti-HIV, and antioxidant activities as well as their influence over central nervous system [1]. A third large area of application of coumarin derivatives are modern technologies. They can be applied as excellent luminophores and laser dyes. Coumarin derivatives may be used as ligands for metal complexes and for modification of organic and inorganic supports.

The investigations on the chemical behavior of the 3-substituted 2-oxo-2H-1-benzopyranes (coumarins) toward nucleophilic reagents represented them as good acceptor in the 1,4-addition reactions. 

Acknowledgements: The support by the project EXTREME, funded by the Bulgarian Ministry of Education and Science, D01-76/30.03.2021 through the program “European Scientific Networks” is gratefully acknowledged.

Reactions of the 3-substituted coumarins with organomagnesium, and organozinc reagents as well as with Ivanov’s reagent were carried out and the corresponding 2-oxochromanes were isolated with good yields. The reactions with their analougs 1,2-benzoxaphosphorine as substrate had the same synthetic progress but in these cases were isolated only two of possible diastereoisomers. The reactions were carried out under ultrasound irradiation and the yields of the target products were higher and the results were accurate and precise. 

Interestingly nucleophilic addition of halogen subsituted anhydride in the presence of Zn lead to formation of biscoumarins. Conditions suggested by us represent a new method for the synthesis of this type of compounds under simple and eco-friendly experimental set up.