Table 1 Optimization of reaction conditions.[a]

From: Modular synthesis of clickable peptides via late-stage maleimidation on C(7)-H tryptophan

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entry

catalyst

additive

oxidant

solvent

3a/3aa yield(%)b

1

[RhCp*Cl2]2

 

Ag2CO3

THF

None/None

2

[RhCp*Cl2]2

AgSbF6

Ag2CO3

THF

41/13

3

[RhCp*Cl2]2

AgBF4

Ag2CO3

THF

15/10

4

[RhCp*Cl2]2

AgNTf2

Ag2CO3

THF

48/15

5

[RhCp*Cl2]2

AgNTf2

Ag2CO3

DCM

55/20

6

[RhCp*Cl2]2

AgNTf2

Ag2CO3

DMF

None/5

7

[RhCp*Cl2]2

AgNTf2

Ag2CO3

DCE

40/14

8

[IrCp*Cl2]2

AgNTf2

Ag2CO3

DCM

15/Trace

9

[Ru(p-cymene)Cl2]2

AgNTf2

Ag2CO3

DCM

Trace/Trace

10

Pd(OAc)2

AgNTf2

Ag2CO3

DCM

None/None

11

[RhCp*Cl2]2

AgNTf2

AgOAc

DCM

27/12

12

[RhCp*Cl2]2

AgNTf2

Ag2O

DCM

83/Trace

13

[RhCp*Cl2]2

AgNTf2

Cu(OAc)2

DCM

Trace/6

14c

[RhCp*Cl2]2

AgNTf2

Ag2O

DCM

53/Trace

15d

[RhCp*Cl2]2

AgNTf2

Ag2O

DCM

78/Trace

  1. aReaction conditions: 1a (0.2 mmol), 2a (0.6 mmol), catalyst (5 mol%), additive (20 mol%), oxidant (1.5 eq), solvent (1.5 mL), 80 °C, 6 h.
  2. b Isolated yields.
  3. c Temperature increased to 100 °C.
  4. d Temperature decreased to 60 °C.
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