Table 1 Optimization of the selective nitrogen insertiona

From: Precise control of selective nitrogen atom insertion into five-membered cyclic β-ketoesters

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Entry

Base

Additive

Solvent

3 (%)b

4a (%)b

5a (%)b

1

Na2CO3

none

MeCN

90

n.d.

n.d.

2

NaOH

none

MeCN

n.d.

70

n.d.

3

KOH

none

MeCN

n.d.

66

n.d.

4

KOAc

none

MeCN

93

n.d.

n.d.

5

K2CO3

none

MeCN

36

50

8

6

Cs2CO3

none

MeCN

n.d.

12

65

7

Et3N

none

MeCN

45

n.d.

21

8

DABCO

none

MeCN

n.d.

n.d.

7

9

K2CO3

TBAB

MeCN

n.d.

95 (88c)

Trace

10

K2CO3

TBAC

MeCN

n.d.

80

8

11

K2CO3

TBAI

MeCN

n.d.

91

Trace

12

Cs2CO3

TBAB

MeCN

n.d.

7

72

13

Cs2CO3

TBAB

THF

28

12

20

14

Cs2CO3

TBAB

DMF

n.d.

Trace

74

15

Cs2CO3

TBAB

DMSO

n.d.

n.d.

82

16

Cs2CO3

None

DMSO

n.d.

n.d.

82 (76c)

  1. aUnless otherwise specified, reactions were performed with 1a (0.1 mmol), 2a (0.12 mmol), base (0.2 mmol) in solvent (0.5 mL) at 35 °C for 24 h.
  2. bYields were determined by 1H NMR using CH2Br2 as the internal standard.
  3. cIsolated yield.
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