Chemistry Reference
In-Depth Information
H
Ar
H
Ar
Ar
Ar
TfOH
O
O
N
N
B
B
H
R
OTf
R
37
H
Ar
Ar
H
Ar
Ar
Methacrolein
O
N
H
B
O
N
H
B
O
R
H
TfO
R
TfO
R = 2-Me-Ph, Ar = Ph:
38a
R = 2-Me-Ph, Ar = 3,5-Me
2
-Ph:
38b
Scheme 8D.63.
H
Ph
Ph
X = OTf:
38a
X = NTf
2
:
39a
B
O
N
H
Me
X
O
H
(20 mol %)
+
Me
OEt
CH
2
Cl
2
CO
2
Et
H
Me
38a
: 4°C, 72 h
>98% ee (46%)
endo
:
exo
= 91/9
39a
: 20°C, 16 h
97% ee (94%)
endo
:
exo
=89/11
Scheme 8D.64.
synthesis of Tamifl u, to provide the corresponding cycloadduct in high yield and enan-
tioselectivity (97%, 97% ee) under neat conditions (Scheme 8D.65) [101].
Recently, Balskus and Jacobsen applied the oxazaborolidine catalyst to the asym-
metric transannular D-A (TADA) reaction that provides polycyclic adducts in enanti-
oselectivity (Scheme 8D.66) [102]. The TADA reaction proceeds smoothly at room
temperature in toluene (0.3 M) by using the catalyst
40
to afford the corresponding
polycyclic adducts in high diastereo- and enantioselectivity. This TADA can be employed
as a key step in the total synthesis of the sesquiterpene 11,12-diacetoxydrimane.
Corey et al. also reported that the oxazaborolidine-aluminum bromide catalyst (
41
)
is exceedingly effective for the asymmetric D-A reactions (Scheme 8D.67) [103]. The
catalyst (
41
) is conveniently prepared
in situ
by the combination of aluminum bromide
