Chemistry Reference
In-Depth Information
Ph
Ph
N
N
Co
+
O
O
O
O
SbF
-
O
O
H
21
(X mol %)
CHCl
3
, -20
+
H
h
C
Ph
°
Ph
COPh
X = 5 (3 h) 93% ee (93%)
X = 0.5 (45 h) 95% ee (80%)
X = 0.2 (80 h) 94% ee (80%)
Scheme 8D.25.
Ph
Ph
N
N
Co
+
t
Bu
t
Bu
O
O
SbF
-
R
R
O
OH
22
(X mol %)
Toluene, r.t.
+
H
2
Et
Ph
Ph
CO
2
Et
22a
: R =
t
Bu
X = 5 (15 h)
46% ee (93%)
22b
: R = TES
X = 5 (2 h)
62% ee (98%)
22c
: R = TIBS
X = 5 (2 h)
98% ee (97%)
92% ee (99%)
X = 0.1 (24 h)
O
OH
22c
(4 mol %)
N
+
N
H
Toluene, r.t., 24 h
>99% ee (84%)
Scheme 8D.26.
(Br, Cl, CN, NO
2
) in particular show higher reactivity and enantioselectivity. BaO
can act as a desiccant rather than as an acid scavenger. Hydrolysis or ozonolysis can
easily transform the vinyl ether portions of the ene products to ketones or esters,
respectively.
Ruck and Jacobsen also examined the asymmetric ene reaction with silyl enol ether
as an enophile (Scheme 8D.28) [52]. In a combination of Cr complex
23b
, MS 4 Å , and
substoichiometric amounts of diisopropylethylamine (DIPEA) to trap a trace amount
of Brønsted acid associated with the catalyst, even simple aliphatic aldehydes have been
converted into the β-hydoxytrimethysilyl enol ether products in high yields and enanti-
