Peroxodisulfate-assisted three-component benzylation of coumarins with styrenes and KSCN: a transition-metal-free approach for the synthesis of 3-(1-aryl-2-thiocyanatoethyl)-2H-chromen-2-one in ethyl lactate

Abstract

Peroxodisulfate-assisted three-component benzylation of coumarins with styrenes and KSCN to 3-(1-aryl-2-thiocyanatoethyl)-2H-chromen-2-one is reported for the first time. This reaction proceeds via the consecutive addition of the SCN radical to styrenes followed by the addition of the resultant substituted-benzylic radical to the C₃-position of coumarin derivatives. In contrast to previous approaches that normally require transition-metal catalysis, toxic volatile organic solvents, bases and elevated temperature, the present strategy of benzylation of coumarins is transition-metal-free and base-free, and applicable under ambient conditions with ethyl lactate as a green medium.