Prominent Ligand Types in Modern Cross-Coupling Reactions - New Trends in Cross-Coupling: Theory and Applications - page 51

Ph

Pd 2 (dba) 3 (1 mol %)
DPEPhos (2 mol %)
NaOtBu

Br

OH

O

THF, 65 °C
70 %

Ph

Ph

Pd 2 (dba) 3 (1 mol %)
DPEPhos (2 mol %)
NaOtBu

Br

N

Toluene, 105 °C, 2h
88 %

NH 2

Ph

Ph

Figure 2.35 Carboetherification (top) and carboamination (bottom) reactions pro-
moted by Pd/DPEPhos.

Pd 2 (dba) 3
DPEPhos
NaOtBu

N

O

N tBu

ArBr

50 - 80 °C, 24 h
46 - 98 %

Ar R

R H

Figure 2.36 Coupling of aryl bromides with N-tert-butylhydrazone as an acyl anion
equivalent.

not suitable for coupling aliphatic amines or N-alkylanilines as large
amounts of hydrodebromination products were observed. DPEPhos has
proven to be a very useful ligand in many amination reactions. 133 It was also
effective in promoting Negishi reactions, 134 regioselective Suzuki-Miyaura
reactions of dihalogenated electrophiles, 135 thioetherification of (hetero)aryl
iodides with (hetero)aryl thiols 136 and a few examples of ketone enolate a-
arylations. 137 Wolfe and co-workers developed a series of interesting car-
boetherification 138 and carboamination 139 reactions in which Pd/DPEPhos is
often the catalyst of choice (Figure 2.35). 140
Takemiya and Hartwig demonstrated that Pd/DPEPhos is uniquely suited
for coupling reactions of aryl bromides and N-tert-butylhydrazone as an acyl
anion equivalent (Figure 2.36). 141

2.3.3 Biaryl Monophosphines
In 1998, Buchwald and co-workers reported the synthesis and use of a novel
electron-rich phosphine ligand [2-dicyclohexylphosphino-2 0 -(N,N-dimethyl-
amino)biphenyl (DavePhos 142 )] for Suzuki-Miyaura, ketone a-arylation and