Table 1 Optimization of A3 coupling reaction conditionsa,b

From: Atomically precise ultrasmall copper cluster for room-temperature highly regioselective dehydrogenative coupling

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Entry

Variations

Conv.

Yield of 4

1

None

100%

99%

2

2 h

65%

65%

3

5 h

100%

99%

4

Cu3NC(BINAP), 5 h

70%

68%

5

Cu3NC(Pz), 5 h

27%

25%

6

5 mol% CuBr, 5 h

50%

48%

7

5 mol% CuCl, 5 h

28%

27%

8

5 mol% Cu2O, 5 h

trace

trace

9

Cu(MeCN)4PF6, 5 h

61%

59%

10

Dioxane as solvent

20%

<10%

11

THF as solvent

30%

15%

12

MeOH as solvent

n.r

n.r

13

MeCN as solvent

70%

53%

14

No copper

n.r.

n.r.

15

NHC ligand

n.r.

n.r.

16

No 4 Å MS

20%

20%

  1. aGeneral reaction conditions: 1 (0.2 mmol, 1.0 equiv.), 2 (0.2 mmol, 1.0 equiv.), 3 (0.3 mmol, 1.5 equiv.), [Cu] catal. (0.005 mmol, 2.5 mol%), activated MS 4 Å sieves (600 mg) in dry solvent (2.0 mL) under N2 at room temperature.
  2. bConversion and yield were determined by 1H NMR using 1,3,5-trimethoxybenzene as an internal standard.
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