Table 1 Optimization Studies of the Atroposelective [4 + 2] Annulation Reactiona

From: Catalytic asymmetric intermolecular [4 + 2] annulation of benzocyclobutenones with Alkynes and activated carbonyls via C—C activation

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entry

Rh catalyst

ligand

solvent

yield (%)

ee (%)

1

[Rh(COD)2]BF4

L1

1,4-dioxane

63

34 (S)

2

[Rh(COD)2]BF4

L2

1,4-dioxane

56

35 (S)

3

[Rh(COD)2]BF4

L3

1,4-dioxane

70

73 (S)

4

[Rh(COD)2]BF4

L4

1,4-dioxane

51

57 (R)

5

[Rh(COD)2]BF4

L5

1,4-dioxane

66

85 (R)

6

[Rh(COD)2]BF4

L5

PhMe

67

84 (R)

7

[Rh(COD)2]BF4

L5

THF

72

90 (R)

8

[Rh(COD)2]BF4

L5

DCE

61

82 (R)

9

[Rh(COD)2]BF4

L5

MTBE

47

68 (R)

10

[Rh(COD)2]OTf

L5

THF

73

94 (R)

11

[Rh(COD)Cl]2

L5

THF

< 3

–

12b

[Rh(COD)2]OTf

L5

THF

39

94 (R)

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  1. aReaction conditions: benzocyclobutenone (0.1 mmol), N-alkynylindole (0.12 mmol), Rh catalyst (8 mol%), and ligand (8 mol%) in a solvent (1 mL) under N2 at 100 °C for 16 h, isolated yield. The ees were determined by HPLC analysis on a chiral stationary phase. bRh catalyst (4 mol%).
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