Choline Hydroxide: An Efficient and Biocompatible Basic Catalyst for the Synthesis of Biscoumarins Under Mild Conditions

Abstract

In this work, choline hydroxide is found to be an efficient and green catalyst for the synthesis of biscoumarins through the Domino Knoevenagel–Michael reaction of a series of aldehydes with 4-hydroxylcoumarin under mild conditions. A series of aldehydes with different substituted functional groups, especially those which are sensitive to acid, have been converted to biscoumarins with good to excellent isolated yields, and the reactions can be easily scaled up to multigrams. The target products can be simply separated by filtration, and the aqueous solution of choline hydroxide (as filtrate) can then be reused for the next run reaction. Choline hydroxide was found to be a green and efficient catalyst for the synthesis of biscoumarins through the Domino Knoevenagel–Michael reactions under mild conditions.