Table 1. Optimization of reaction conditions^a.

S. no.	Base	Solvent	Temp./time	Yield (3a)	Yield (3a′)
1	K2CO3	1,4-Dioxane	60 °C, 6 h	20%	—
2	K2CO3	THF	60 °C, 6 h	40%	—
3	Cs2CO3	1,4-Dioxane	60 °C, 6 h	24%	—
4	Cs2CO3	THF	60 °C, 6 h	50%	—
5	Cs2CO3	THF–H2O (5 : 2)	60 °C, 6 h	60%	—
6	Na2HPO4	THF	60 °C, 6 h	82%	—
7	Na2HPO4	THF–H2O (5 : 2)	60 °C, 6 h	91%	1%
8	Na2HPO4	THF–H2O (4 : 3)	60 °C, 6 h	80%	2%
9	Na2HPO4	THF–H2O (3 : 4)	60 °C, 6 h	75%	Trace
10	TEA	THF	60 °C, 6 h	Trace	Trace

^aReaction conditions: 1a (0.0187 mmol), 2 (0.0187 mmol), Na₂HPO₄ (0.02 mmol), 6 h, and temperature 60 °C in sealed tube.