Table 3. Optimization Studies for Cross-Coupling of Phenyl Carbamate with Phenylboronic Acid^a.

entry	base (equiv)	solvent	temp (°C)	yield (%)b
1	NaOC2H4OH(2.0)	H2O	reflux	43
2	NaOC2H4OH(2.0)	ethanol	reflux	56
3	NaOC2H4OH(2.0)	n-PrOH	reflux	52
4	NaOC2H4OH(2.0)	EG	100	91
5	NaOC2H4OH(2.0)	glycerol	100	73
6	NaOC2H4OH(2.0)	dioxane	reflux	37
7	K3PO4 (2.0)	EG	100	83
8	NaOH (2.0)	EG	100	72
9	K2CO3 (2.0)	EG	100	80
10	Cs2CO3 (2.0)	EG	100	79
11	DBU (2.0)	EG	100	69
12	DABCO (2.0)	EG	100	66
13	NaOtBu (2.0)	EG	100	89
14	NaOC2H5 (2.0)	EG	100	84
15		EG	100	0
16	NaOC2H4OH(1.0)	EG	100	70
17	NaOC2H4OH(1.5)	EG	100	79
18	NaOC2H4OH(2.5)	EG	100	90
19	NaOC2H4OH(3.0)	EG	100	91

^aReaction conditions: phenyl carbamate (1 mmol), phenylboronic acid (1 mmol), base, Fe₃O₄@SiO₂–EDTA–Ni(II) catalyst(0.018 g, 1 mol %), solvent, 6 h

^bIsolated yield.