Chemistry Reference
In-Depth Information
B(OR)
2
HBPin (
127
) or HBCat (
102
)
Ph
Ph
[R h( co d)
2
]BF
4
,(
R
)-(
S
)-josiphos
THF, 25 C
133
6
Me
%eeof
133
84 (
S
)
60 (
R
)
PCy
2
HBPin (
127
)
HBCat (
102
)
Fe
PPh
2
(
R
)-(
S
)-josiphos (
110
)
Scheme 9.29.
Chiral monodentate phosphite
134
and phosphoramidite
135
derived from taddol
were examined to afford high enantioselectivity and moderate regioselectivity in
rhodium-catalyzed asymmetric hydroboration of vinylarenes with pinacolborane
(Scheme 9.30 ) [69] .
1) [RhCl(nbd)]
2
(2 mol % Rh), L*
DME, rt, 17 h
OH
O
+
H
B
Ph
Ph
2) H
2
O
2
, NaOH
O
6
127
8
Ph
Ph
Ph
Ph
yield
75%
79%
%eeof
8
95 (
R
)
96 (
R
)
L*
134
135
O
O
O
Ph
O
Ph
P
O
P
N
O
O
O
Bn
O
Ph
Ph
Ph
Ph
L* = (
S
,
S,R,S
)-
134
(
S
,
S
)-
135
Scheme 9.30.
9.4. ASYMMETRIC HYDROALUMINATION AND HYDROSTANNATION
OF ALKENES
Hydroalumination and hydrostannylation of olefi ns have attracted signifi cant interests
for their synthetic utility [47e,70]. While asymmetric hydrosilylation and hydroboration
of alkenes catalyzed by transition metal are well known, examples of asymmetric ver-
sions of catalytic hydroalumination and hydrostannation of alkenes using transition
metal catalysts have been rare to date.
Highly enantioselective catalytic hydroalumination of oxabicyclic alkenes was
reported as using chiral nickel catalyst [71]. The reaction of
136
with
iso
- Bu
2
AlH cata-
lyzed by a nickel complex of (
R
)-binap at rt gave the ring-opening product
137
in 97%
ee (Scheme 9.31 ).
