Dihydrobenzosiloles were prepared in high yields and excellent
enantioselectivities by the dehydrogenative silylation of primary C(sp
3 )ÀH bonds,
using [Ir(μ-OMe)(COD)] 2 and adequate N,N-chiral ligands in the presence of NBE
(Scheme 46). The resulting silylated products were transformed into halocarbon and
hydroxylated compounds. It is noteworthy that this methodology proved efficient for
(CO) n Ir
H
(CO) Ir
n
Ir(CO) n
SiEt 3
H
SiEt 3
H
(CO) n Ir
SiEt 3
H
or
N
H
SiEt 3
N
(CO)n Ir
H
H
NBA
N
SiEt 3
NBE
"SiEt 3 " transfer
N
SiEt 3
Scheme 43 Catalytic cycle proposed for the benzylic silylation of 4-methylpyridine
61/NaBArF 4
3,5-dimethylpyridine
X
N
X
N
SiEt 3
(
t
Bu) 2 P
Ir
P(
t
Bu) 2
O
O
H
Cl
53
Et 3 SiH
cyclopentene
R
R
X = O, S, NMe
Scheme 44 Silylation of 2-alkyl-1,3-azoles catalyzed by 53/NaBAr
F
4
[Ir(µ-OMe)(COD)] 2 (5 mol%)
Cyclohexene, 160 ºC, 24 h
5,6-Me 2 phen (10 mol%)
Si
R
2
R
1
Si
R
2
R
1
Si
R
2
R
1
Scheme 45 Dimerization of benzylmethylsilanes by dehydrogenative silylation
[Ir(µ-OMe)(COD)] 2 (2 mol%)
NBE, Et 2 O, 50 ºC
Ligand (4.5 mol%)
Si
H
R
2
Si
R 2
R
1
R
1
N
N
O
Ligand
Scheme 46 Preparation of dihydrobenzosiloles by intramolecular C(sp
3
) À H silylation
264
M. Iglesias and L. A. Oro