Table 1 Selected Optimization Resultsa,b

From: A facile synthesis of α,β-unsaturated imines via palladium-catalyzed dehydrogenation

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Entry

Deviation from standard conditions

Yield of 2 (%)

Yield of 3 (%)

1

None

84 (74%)d

5

2

under N2

85

7

3

no HOAc

74

10

4

Dppf instead of DPEPhos

51

7

5

BINAP instead of DPEPhos

21

3

6

no DPEPhos

0

4

7

Pd(PPh3)2Cl2 instead of Pd(OAc)2

0

2

8

Pd(PPh3)4 instead of Pd(OAc)2

0

25

9

Pd2(dba)3 instead of Pd(OAc)2

36

6

10

Cu(OAc)2 instead of Pd(OAc)2

0

40 (10 of 1)c

11

Fe(OTf)2 instead of Pd(OAc)2

0

32 (40 of 1)c

12

Ni(acac)2 instead of Pd(OAc)2

0

16 (68 of 1)c

13

no BQ

45

42

14

selectfluor instead of BQ

8

16

15

mCPBA instead of BQ

5

43

16

LPO instead of BQ

5

13

17

BQ (0.2 equiv) under O2 atmosphere

58

30

18

THF instead of dioxane

63

8

19

DCE instead of dioxane

27

17

20

DMSO instead of dioxane

13

32

21

no Pd(OAc)2

0

0 (85 of 1)c

22

Et3N or K2CO3 (1.0 equiv) instead of HOAc

0

0 (70 or 63 of 1)c

  1. BQ 1,4-benzoquinone, DPEPhos bis[2-(diphenylphosphino)phenyl]ether, Dppf 1,1’-bis(diphenylphosphino)ferrocene, BINAP 1.1’-binaphthyl-2.2’-diphemylphosphine, dba dibenzylideneacetone, mCPBA 3-chloroperoxybenzoic acid, LPO lauroyl peroxide.
  2. aStandard reaction conditions: a mixture of 1 (0.20 mmol), Pd(OAc)2 (0.02 mmol), DPEPhos (0.022 mmol), HOAc (0.20 mmol), and BQ (0.20 mmol) in dioxane (1.0 mL) was stirred under air at 70 °C for 15 min.
  3. bIsolated yields.
  4. cThe recovery of starting material 1.
  5. dThe yield in a 5.0 mmol scale.
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