Entry

R₁

R₂

R₃

Yield(%)^b

m.p. (^oC)

3a

H

H

H

90

145~146

3b

5-CH₃

H

H

89

3c

5-C₆H₅

H

H

85

120~122

3d

5-CH₃

5-CH₃

H

89

3e

H

H

4-F

79

129~130

3f

H

H

4-Cl

86

69~71

3g

H

H

4-NO₂

60

106~107

3h

H

H

2-NO₂

45

126~127