Entry

Catalyst

Solvent

Temperature

Time (min)

Yield (%)^a

1

without DBSA

H₂O

reflux

240

trace

2

DBSA (25%)

H₂O

reflux

75

85

3

DBSA (25%)

EtOH

r.t.

120

trace

4

DBSA (25%)

EtOH

reflux

60

87

5

DBSA (25%)

MeOH

reflux

105

80

6

DBSA (25%)

EtOH:H₂O (1:1)

reflux

40

94

7

DBSA (25%)

MeOH:H₂O (1:1)

reflux

65

90

8

DBSA (25%)

EtOH:H₂O (1:1)

r.t.

40

trace

9

DBSA (10%)

EtOH:H₂O (1:1)

reflux

40

68

10

DBSA (15%)

EtOH:H₂O (1:1)

reflux

40

70

11

DBSA (20%)

EtOH:H₂O (1:1)

reflux

40

72

12

DBSA (30%)

EtOH:H₂O (1:1)

reflux

40

93

13

DBSA (25%)

EtOH:H₂O (1:1)

MV condition

12

95