Entry

Solvent

C/S

Temp.

Yield (%)d

Ee (%)e

1a

MeOH

0.5%

r.t.

Trace

ND

2 a

CH2Cl2

0.5%

r.t.

Trace

ND

3 a

THF

0.5%

r.t.

Trace

ND

4 a

EtOAc

0.5%

r.t.

27

45

5 a

t-BuOMe

0.5%

r.t.

42

60

6 a

DMF

0.5%

r.t.

74

79

7

DMF

0.5%

-20˚C

66

84

8

DMF

0.5%

-40˚C

Trace

ND

9b

DMF

0.25%

-20˚C

38

75

10c

DMF

1%

-20˚C

72

83