Table 1 Optimization of reaction conditionsa

From: Palladium catalyzed ortho-C(sp2)–H activation/cyclization of aryl amines assisted by imine and vinylacetic acid

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Entry

[Pd]

Solvent

Yield (%)

dr (4a:4a’)

1

Pd(TFA)2

MeCN

53

12.0:1

2

PdCl2

MeCN

n.d.

–

3

Pd(OAc)2

MeCN

Trace

–

4

Pd(PPh3)4

MeCN

Trace

–

5

Pd(dba)2

MeCN

Trace

–

6

Pd(TFA)2

1,2-DCE

43

11.1:1

7

Pd(TFA)2

toluene

29

13.3:1

8

Pd(TFA)2

HFIP

70

12.9:1

9

Pd(TFA)2

AcOH

84

11.2:1

10

Pd(TFA)2

DMF

Trace

-

11

Pd(TFA)2

DMSO

45

> 20.0:1

12 b

Pd(TFA)2

DMSO

80

> 20.0:1

13 b

–

DMSO

n.d.

–

14 b,c

Pd(TFA)2

DMSO

<5

–

  1. dr diastereoselectivity, n.d. not detected, TBHP tert-butyl hydroperoxide, 2,9-dmphen 2,9-dimethyl-10-phenanthroline, HFIP 1,1,1,3,3,3-hexafluoro-2-propanol, 2,6-DMBQ 2,6-dimethoxy-1,4-benzoquinone.
  2. aReaction conditions: 1a (0.25 mmol), 2a (1.5 equiv.), 3 (1.5 equiv.), [Pd] (10 mol%), 2,9-dmphen (15 mol%), TBHP (1.0 equiv., 5.5 mol/L in decane), solvent (0.5 M), at 35 °C under air for 12 h. Yield and dr (4a:4a’) ratio were determined by 1H NMR of the crude product with MeNO2 as internal standard.
  3. bWith 5 mol% Pd(TFA)2, 2,6-DMBQ (1.0 equiv.), without 2,9-dmphen, and the reaction mixture was heated for 24 h.
  4. cWithout oxidant and under N2.
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