Chemistry Reference
In-Depth Information
34
(10 mol %)
Yb(OTf)
3
(20 mol %)
O
X
O
O
O
Et
X
OR
AcOH (10 eq.)
Et
2
O, r.t., 12 h
89% ee (86%)
93% ee (80%)
85% ee (95%)
R = Et
X = H
Me
I
O
Ar
2
P
OTf
O
O
90% ee (80%)
94% ee (81%)
R = allyl
X = H
Me
Pd
2+
OTf
P
Ar
2
O
34
(
R
)-DM-SEGPHOS
(Ar = 3,5-
t
Bu
2
-4-OMe-C
6
H
2
)
Scheme 8D.55.
O
Me
PPh
2
PPh
2
R
35
(6.0 mol %)
O
TMS
TMS
[Rh(coe)
2
Cl]
2
(2.5 mol %)
O
O
Me
H
Me
35a
: R = Ph
87% ee (76%)
35
(6.0 mol %)
H
Me
[Rh(coe)
2
Cl]
2
(2.5 mol %)
Me
O
O
H
35b
: R = Me
73% ee (84%)
35c
: R =
t
Bu
54% ee (72%)
35a
: R = Ph
47% ee (73%)
Scheme 8D.56.
fused rings [88-90]. The fused structures thus obtained can be inducted into a variety of
natural products whose syntheses are diffi cult without the use of transition metals.
Therefore, a number of catalyst systems such as Rh complexes that perform intramo-
lecular [4 + 2] cycloaddition in excellent yields have been developed over 15 years, and
some asymmetric variants using chiral diphosphine or diene ligands have also been
developed [91] .
Livinghouse et al. reported the fi rst examples of catalytic asymmetric intramolecular
[4 + 2] cycloaddition with unreactive diene - yne or diene - ene (Scheme 8D.56 ) [92] . In
