Table 1 Optimization of reaction conditionsa

From: Nucleophilic aromatization of monoterpenes from isoprene under nickel/iodine cascade catalysis

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Entry

Cat. 1

Cat. 2

Additives

Sol. A

Sol. B

3a + 4a (%)

5a (%)

6 + 7 (%)

8a (%)

1b

Ni(cod)2

I2

K2S2O8

THF

33

20

–

–

2b

Ni(cod)2/IPr·HCl/NaOtBu

I2

K2S2O8

THF

2

–

–

–

3c

Ni(cod)2/IPr·HCl/NaOtBu

I2

K2S2O8

THF

29

5

–

–

4

Ni(cod)2/IPr·HCl/NaOtBu

I2

K2S2O8

THF

–

–

1

28

5

Ni(cod)2/dppe

I2

K2S2O8

THF

16

6

–

–

6d

Ni(cod)2/PCy3

I2

K2S2O8

THF

–

–

6

3

7

Ni(cod)2/IMes·HCl/NaOtBu

I2

K2S2O8

THF

3

–

2

1

8

Ni(cod)2/IPr·HCl/NaOtBu

I2

K2S2O8

PhMe

THF

–

–

3

48

9

Ni(cod)2/IPr·HCl/NaOtBu

I2

K2S2O8

n-hexane

THF

–

–

3

51

10

Ni(cod)2/IPr·HCl/NaOtBu

I2

K2S2O8

n-hexane

1,4-dioxane

–

–

42

13

11

Ni(cod)2/IPr·HCl/NaOtBu

I2

DMSO

n-hexane

THF

–

–

–

–

12

Ni(cod)2/IPr·HCl/NaOtBu

NIS

K2S2O8

n-hexane

THF

–

–

–

–

13

Ni(cod)2/IPr·HCl/NaOtBu

I2

KI/K2S2O8

n-hexane

THF

–

–

4

58

14

Ni(cod)2/IPr·HCl/NaOtBu

I2

KI/Na2S2O8

n-hexane

THF

–

–

4

64

15

Ni(cod)2/IPr·HCl/NaOtBu

I2

KI/AdCO2H

Na2S2O8

n-hexane

THF

–

–

7

68

16e

Ni(cod)2/IPr·HCl/NaOtBu

I2

KI/(PhO)2PO2H

Na2S2O8

n-hexane

THF

–

–

5

82

  1. aReaction conditions: Step I: 2a (1.2 mmol), [Ni]/ligand (5.0 mol%), base (10 mol%), solvent A (0.50 mL), 100 oC, 12 h; Step II: 1a (0.20 mmol), I2 or NIS (20 mol%), oxidant (2.0 equiv.), KI/acid (10 mol%), solvent B (0.50 mL), 100 oC, 18 h. Yield and selectivity were determined by GC-FID analysis with trimethoxybenzene as the internal standard.
  2. bOperated in one-step procedure, 80 oC, 18 h.
  3. c80 oC.
  4. dLigand (10 mol%).
  5. e24 h for the second step.
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