Table 1 Optimization of the reaction conditions for the enantioselective photocyclization of 1a

From: Energy transfer-enabled enantioselective photocyclization using a privileged Al–salen catalyst

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Entry

Catalyst

Solvent

Additive (1.5 equiv.)

T (°C)

Yield 2a (%)

d.r. (trans:cis)

e.r. trans

e.r. cis

1

Al-1

DCM

–

r.t.

44

71:29

74:26

68:32

2

Al-2

DCM

–

r.t.

95

55:45

63:37

55:45

3

Al-3

DCM

–

r.t.

64

64:36

67:33

53:47

4

Al-4

DCM

–

r.t.

83

63:37

67:33

57:43

5

Al-5

DCM

–

r.t.

15

66:34

84:16

80:20

6

Al-6

DCM

–

r.t.

14

71:29

65:35

54:46

7

Al-7

DCM

–

r.t.

42

67:33

23:77

27:73

8

Al-8

DCM

–

r.t.

36

71:29

73:27

75:25

9

Al-1

Acetone

–

r.t.

<5

ND

ND

ND

10

Al-1

MeCN

–

r.t.

33

56:44

64:36

62:38

11

Al-1

Toluene

–

r.t.

33

67:33

64:36

56:44

12

Al-1

DCM

nBu4NCl

r.t.

67

67:33

78:22

80:20

13

Al-1

DCM

HFIP

r.t.

95

51:49

67:33

67:33

14a

Al-1

DCM

nBu4NCl

−20

50

64:36

82:18

85:15

15a,b

Al-1

DCM

nBu4NCl MS (3 Å)

−20

55

62:38

82:18

88:12

16a,b,c

Al-1

DCM

nBu4NCl MS (3 Å)

−20

57

66:34

84:16

90:10

17a,c,d

Al-1

DCM

nBu4NCl MS (3 Å)

−20

67

66:34

84:16

90:10

  1. Unless stated otherwise, reactions were performed with 1a (0.1 mmol), Al–salen catalyst (10 mol%) and additive (1.5 equiv.) in dichloromethane (DCM) under an argon atmosphere. Irradiation took place at 400 nm, and for irradiation at −20 °C a glass rod was used as an optical guiding rod. Isolated yields of combined trans- and cis-2a are reported. The d.r. was determined by 1H NMR spectroscopy; the e.r. was determined by high-performance liquid chromatography (HPLC) analysis on a chiral stationary phase. aReactions at −20 °C were run for 21 h; b15 mg of molecular sieves were used; c20 mol% of catalyst was used; d6 mg of molecular sieves were used. r.t., room temperature; ND, not determined.
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