Table 2 Discovery and evaluation of the Cu-catalyzed asymmetric cascade processa.

From: Enantioselective Cu-catalyzed double hydroboration of alkynes to access chiral gem-diborylalkanes

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Entry

Catalyst

Ligand

Solvent (mL)

Additive (equiv)

Yield (%)b

er c

1

Co(acac)2

Xantphos

THF (0.2)

—

76

—

2

Co(acac)2

(R,R)-Walphos

THF (0.2)

—

33

39:61

3

Co(acac)3

(R,R)-Walphos

THF (0.2)

—

28

35:65

4

Cu(acac)2

(R,R)-Walphos

THF (0.2)

—

20

76:24

5

Cu(acac)2

(R,S)-Josiphos

THF (0.2)

—

25

32:68

6

Cu(acac)2

(R)-tol-BINAP

THF (0.2)

—

15

45:55

7

Cu(acac)2

(S,S)-Me-duphos

THF (0.2)

—

n.d.

—

8

Cu(acac)2

(R,R)-Me-ferrocelane

THF (0.2)

—

n.d.

—

9

Cu(acac)2

(R,R)-Walphos

Cyclohexane (1.0)

—

33

88:12

10

Cu(acac)2

(R,R)-CH3-Walphos

Cyclohexane (1.0)

—

16

72:28

11

Cu(acac)2

(R,R)-tBu-Walphos

Cyclohexane (1.0)

—

17

62:38

12

Cu(acac)2

(R,R)-CF3-Walphos

Cyclohexane (1.0)

—

18

86:14

13

Cu(acac)2

(R,R)-Nap-Walphos

THF (0.2)

—

23

84:16

14d

Cu(acac)2

(R,R)-Walphos

Cyclohexane (1.0)

PMHS (1.0)

78

94:6

  1. aAfter catalyst (4 mol%), ligand (4 mol%), HBdan (0.24 mmol) were mixed in 0.2 mL of THF at room temperature for 15 min, HBpin (0.3 mmol) and 1 (0.2 mmol) were added subsequently at room temperature, then the resulting mixture was stirred at ambient temperature for 24 h.
  2. bIsolated yield.
  3. cThe enantioselectivity was determined by Chiral HPLC.
  4. dAfter catalyst (6 mol%), ligand (6 mol%), HBdan (0.24 mmol) and PMHS (1.0 equiv) were mixed in 1.0 mL of cyclohexane at room temperature for 10 min, HBpin (0.3 mmol) and 1 (0.2 mmol) were added subsequently at room temperature, then the resulting mixture was stirred at ambient temperature for 60 h.
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