Compound

R⁵

R⁶

R⁷

R⁸

Reaction time (h)

Yield (%)^a

5a

H

H

H

MeO

4

92

5b

H

H

Et₂N

H

4

87

5c

H

H

OH

H

7

61

5d

H

H

4

73

5e

H

H

H

H

4

72

5f

H

H

MeO

H

6

84

5g

H

Br

H

Br

6

55

5h

H

H

H

EtO

6

93