Table 1 The optimization of intramolecular Michael addition/Wittig reaction

From: Enantioselective synthesis of cis-hydrobenzofurans bearing all-carbon quaternary stereocenters and application to total synthesis of (‒)-morphine

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Entry

Catalyst

Additive

T [°C]

t [h]

Yield [%]a

d.r.b

ee [%]c

1

1

A1

rt

72

trace

−

−

2

2

A1

rt

72

60

3.1:1

−34

3

3

A1

rt

24

68

1.5:1

36

4

4

A1

rt

72

28

4.1:1

−66

5

5

A1

rt

2

71

1.9:1

62

6

6

A1

rt

1

73

3.1:1

72

7

6

A1

−10

10

78

5.2:1

78

8

6

A1

−20

24

82

7.1:1

80

9

6

A2

−20

20

83

6.9:1

89

10

6

A3

−20

20

86

7.4:1

95

11

6

A4

−20

40

76

8.7:1

88

12

6

A3

−30

48

87

10.2:1

96

13

6

A3

−40

96

85

11.8:1

96

  1. Reaction was performed with substrate 7 (0.1 mmol), catalyst (10 mol %), and additive (20 mol %) in 1.0 mL of CH2Cl2, and followed by addition of Ph3P = CHCO2Et
  2. aIsolated yield
  3. bDetermined by 1H NMR prior to the addition of Ph3P = CHCO2Et
  4. cDetermined by chiral HPLC
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