Entry

Catalyst

Solvent

Time

Yield (%)^b

1

[C₂O₂BBTA]Cl (20% mol)

-

40 min

85

2

[C₂O₂BBTA][TFA] (20% mol)

-

40 min

96

3

CF₃COOH (20% mol)

-

40 min

96

4

[C₂O₂BBTA][TFA] (10% mol)

-

40 min

85

5

[C₂O₂BBTA][TFA] (30% mol)

-

40 min

95

6

[C₂O₂BBTA][TFA] (20% mol)

H₂O

40 min

5

7

[C₂O₂BBTA][TFA] (20% mol)

MeOH

40 min

6

8

[C₂O₂BBTA][TFA] (20% mol)

EtOH

40 min

10

9

[C₂O₂BBTA][TFA] (20% mol)

i-PrOH

40 min

48

10

[C₂O₂BBTA][TFA] (20% mol)

CH₂Cl₂

40 min

16

11

[C₂O₂BBTA][TFA] (20% mol)

CH₃CN

40 min

19

12

[C₂O₂BBTA][TFA] (20% mol)

DMF

40 min

0

13

[C₂O₂BBTA][TFA] (20% mol)

Toluene

40 min

5

14

[C₂O₂BBTA][TFA] (20% mol)

-

50 min

91

15

[C₂O₂BBTA][TFA] (20% mol)

-

60 min

93

16

[C₂O₂BBTA][TFA] (20% mol)

-

30 min

94

17

[C₂O₂BBTA][TFA] (20% mol)

-

20 min

91