Direct Arylation via C–H Activation - New Trends in Cross-Coupling: Theory and Applications - page 579

[Rh(COD)Cl] 2 (5 mol%)
Na 2 CO 3 (2 equiv)
molecular sieves (4Å)
xylene,145°C,16h

+ CO

+

ArCOCl

N

N

1.5 equiv

Ar

N

N

N N

1-Nap
68%

Ph

NO 2

93% Cl 87%

95%

Scheme 12.56 Rh-catalyzed C-H functionalization of benzo[h]quinoline using an
acid chloride.

[Rh(COD)Cl] 2 (5 mol%)
Na 2 CO 3 (2 equiv)
molecular sieves (4Å)
o- xylene, 145 °C, 9h

O O

+ CO

+ Ph

N

N

O Ph

Ph

1.5 equiv

92%

Scheme 12.57 Rh-catalyzed C-H functionalization of benzo[h]quinoline using an
acid anhydride.

conditions were found also to be applicable for acid anhydrides instead of
acid chlorides (Scheme 12.57). 85

12.3.2 Ortho-Arylation of Phenols
In the case of ortho-metallation of phenols, the challenge lies in the for-
mation of a four-membered metallacycle with the phenol itself. This chal-
lenge was solved by Bedford et al. in 2003, when they accomplished the
ortho-arylation of phenols with aryl halides using a catalytic amount of
Wilkinson's catalyst and phosphinite ligand (Scheme 12.58). 86
According to their proposal, the aryl halide first interacts with Rh I L n ,
forming ArRh III XL n . In the next step, the phosphinite coordinates to the
metal center and a base-mediated orthometallation occurs at the ligand's
phenolate part, forming a five-membered chelating complex. Subsequent
reductive elimination regenerates the Rh I L n species with the release of an
arylated phosphinite. Further phosphinyl group transfer between the phenol
and arylated phosphinite ligand results in an arylated phenol along with
regeneration of phosphinite co-catalyst (Figure 12.16). 86
Notably, this protocol was confined to phenols having one ortho substi-
tution. Bedford and Limmert reported an improved protocol for the aryla-
tion of phenol and its derivatives using [Rh(COD) 2 Cl] 2 as catalyst and
P(NMe 2 ) 3 as ligand, where the diarylated phenol was formed as the major
product (Scheme 12.59). 87
Oi et al. independently reported a similar catalytic system for the ortho-
arylation of both substituted and unsubstituted phenols (Scheme 12.60). 88
A related Pd-catalyzed reaction in an intramolecular set-up was previously