Handbook of Functionalized Organometallics Applications in S

Ar H
Ar =
O
HB
O
CF 3
CF 3
3.2 Preparation and Reaction of Functionalized Aryl and Heteroaryl Boranes
30
Cp*Rh(η4-C6Me6) (2.0 mol %)
cyclohexane, 150 ºC
OMe
NMe 2
NMe 2
NMe 2
Ar
OMe
OMe
O
B
O
N
Si(iPr) 3
88 % 75 % 69 % 82 % 81 %
Scheme 3.17 Direct borylation of aromatics with pinacol borane (30).
Miyaura has demonstrated that the iridium complex derived from the reaction
of [Ir(OMe)(COD) 2] with 4,4¢-di-ter-butyl-2,2¢-bipyridine is a highly active catalyst
for aromatic C-H borylation by bis(pinacol)diborane (37) allowing for the first
time, room-temperature borylation with stoichiometric amount of arenes [31]. The
reactions are tolerated with a wide range of functionalities such as MeO, I, Br, Cl,
CO 2Me, CN and CF 3 yielding aryl boronates in highly regioselective fashion.
Thus, the reaction occurs regioselectively with disubstituted arenes and 1,2-, 1,3and
1,4-dichlorobenzenes are yielding a single product. The borylation of 1,3- disubstituted
benzenes bearing electron donating or electron withdrawing groups
occurs only at the meta position (Scheme 3.18).
Ar H
Ar =
O
B
O
Cl
Cl
I
Cl
37
O
B
O
Cl
1/2[Ir(OMe)(COD)] 2/dtbpy(3 mol %)
hexane, 25 ºC
Cl Cl
Br
Cl CN
82 % 53 % 84 % 83 % 80 %
CF 3
Br
CF 3
OMe
82 % 91 % 81 %
Scheme 3.18 Synthesis of functionalized aryl boronic esters
by transition-metal-catalyzed C-H borylation of arenes.
DTBPy =
Cl
Ar
CO 2Me
But
H 2
O
B
O
N
N
55
CF 3
CN
84 %
tBu
H 2