Table 1. Optimization of Reaction Conditions^a.

entry	variation from the standard condition	yield of 6a/7 (%)b
1	none	80/4
2	B instead of A	25/22
3	C instead of A	<1/19
4	D instead of A	<1/27
5	E instead of A	27/34
6	reaction at room temperature	55/3
7	Cs2CO3 instead of K2CO3	60/20
8	NEt3 instead of K2CO3	50/40
9	DBU instead of K2CO3	44/33
10	20 mol % of K2CO3, 10 mol % of NHC	67/5
11	1 equiv of K2CO3	60/17
12	CH3CN instead of THF	10/26
13	1,4-dioxane instead of THF	53/32
14	toluene instead of THF	20/15
15	1 equiv of 4a	65/5

^aReaction conditions: 5 (1.0 equiv, 0.35 mmol), 4a (1.5 equiv, 0.52 mmol), pre-NHC catalyst A (15 mol %), K₂CO₃ (50 mol%), solvent (2 mL), 4 h, under argon atmosphere.

^bIsolated yields.