Optimization of the reaction conditions^a.

Entry	Solvent	Time (h)	Yieldb (%)
1	DCE	12	Trace
2	Toluene	12	58
3	THF	12	72
4	MeOH	12	78
5	DMSO	1.5	89
6	MeCN	12	81
7	DMF	4	85
8	HFIP	12	Trace
9	Chlorobenzene	12	69
10c	DMSO	12	62
12d	DMSO	1	95
14e	DMSO	12	89

^aReaction conditions: 1a (0.2 mmol), 2 (0.4 mmol), 3a (0.4 mmol) in solvent (2 mL) at 70 °C.

^bYield refers to isolated products after column chromatography.

^cReaction was performed at 40 °C.

^d1.2 equiv. of 2 and 3a were used.

^e10 mmol of 1a were used. HFIP = hexafluoroisopropanol.