Table 1.

Optimization of reaction conditions.

Entry	x	Catalyst	Oxidant	Solvent	Yield [%][a]
1	1.6	L1CuCl2	DTBP	Cumene 1.5 mL	20
2	4.8	L1CuCl2	DTBP	Cumene 1.5 mL	38
3	9.5	L1CuCl2	DTBP	Cumene 1.5 mL	55
4	9.5	L1CuCl2	DTBP	Cumene 1.0 mL	60(62)
5	9.5	L1CuCl2	DTBP	Cumene 0.5 mL	55
6	9.5	L1CuCl2	DTBP	Benzene 1.0 mL	34
7	9.5	L1CuCl2	DTBP	Toluene 1.0 mL	58
8	9.5	L1CuCl2	DTBP	t Bu‐benzene 1.0 mL	29
9	9.5	L1CuCl2	TBHP	Cumene 1.0 mL	trace
10	9.5	L1CuCl2	TBPB	Cumene 1.0 mL	trace
11	9.5	Cu(TC) [c]	DTBP	Cumene 1.0 mL	34
12[b]	9.5	CuF2+L1	DTBP	Cumene 1.0 mL	42
13[b]	9.5	CuCl2+L2	DTBP	Cumene 1.0 mL	12
14[b]	9.5	CuCl2+L3	DTBP	Cumene 1.0 mL	29
15[b]	9.5	CuCl2+L4	DTBP	Cumene 1.0 mL	12

[a] The yield was determined by ¹H NMR analysis of the crude reaction mixture using 1,3,5‐trimethoxybenzene as an internal standard. [b] The amount of ligand was 15 mol %. [c] thiophene‐2‐carboxylate.