Standardization of reaction conditions for the synthesis of 3,3′-(arylmethylene)bis(4-hydroxy-2H-chromen-2-ones).

Entry	Catalyst (mol%)	Solvent	Time (h)	Yield (%)
1	No catalyst	Solvent-free	24	Nil
2	No catalyst	EtOH	6	22
3	Camphor sulfonic acid (20 mol%)	EtOH	6	78
4	Camphor sulfonic acid (20 mol%)	MeOH	6	72
5	Camphor sulfonic acid (20 mol%)	H2O	6	61
6	Camphor sulfonic acid (20 mol%)	EtOH : H2O (1 : 1 v/v)	2	94
7	Camphor sulfonic acid (15 mol%)	EtOH : H2O (1 : 1 v/v)	2	86
8	Camphor sulfonic acid (20 mol%)	EtOH : H2O (1 : 1 v/v)	2	94