Ultrasound-Assisted Metal-Mediated Method for the Formation of Tetrahydro-3,3′-Disubstituted Biscoumarins

Abstract

A new method for faster and simple preparation of 3,3′,4,4′-tetrahydro-3,3′-disubstituted-4,4′-biscoumarins with participation of an organozinc reagent is reported. The reaction is promoted by ultrasound irradiation and it offers a simple experimental setup and excellent reproducibility of the results. Moreover, homodimers were isolated in yields of 45⁻92%. The dimerization conditions are applicable to coumarins with electron-withdrawing groups at third position.

Keywords

• coumarins
• biscoumarins
• organometallic reagents
• radical coupling
• homodimerization
• ultrasound irradiation
• aci-nitro tautomer