Chemistry Reference
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5 mol %
i-Pr
i-Pr
N
Me
Mo
O
Ph
Me
H
O
H
Me
Bicyclic product
formed in 54% yield
and 92% ee
in the absence of
styrene
O
Me
O
+
H
O
Me
1a
H
Ph
<2%
Ph
65% yield, >98% E
>98% ee
C
6
H
6
, 22
°
C, 12 h
Ph
Ph
5 mol %
MesN
N
I
H
Ru
O
O
Oi-Pr
12b
O
H
Ph
Ph
Ph
52% yield, >98% E
90% ee
THF, 22
°
C, 1 h
O
[Ru]
Ph
Scheme 8E.11.
Mo - and Ru - catalyzed enantioselective ROCM of norbornenes.
8E.3.3. Ru - and Mo - Catalyzed Enantioselective ROCM of Oxabicycles: Application
to Total Synthesis of Baconipyrone C
Metal-catalyzed ROCM can be utilized to establish multiple stereogenic centers in a
single transformation through desymmetrization of relatively simple
meso
substrates.
Application of Ru-catalyzed enantioselective ROCM to processes involving
meso
-
oxabicycles was disclosed in 2004 [39]; a report detailing Mo-catalyzed variants of these
catalytic transformations appeared in 2007 [40]. Illustrative examples are provided in
Table 8E.4 .
Endo
-substituted oxabicycles (entries 1 and 2) react readily in the presence of
11b
and
12b
(
98% conversion with 5 mol % catalyst within 1-1.5 h) to provide the desired
products with excellent enantioselectivities. With Ru catalysts, the reaction can be per-
formed in the presence of a secondary alcohol; Mo-based catalysts, however, typically
decompose in the presence of free hydroxyl groups, and protection of the alcohol as the
benzyl ether gives rise to oligomerization of the substrate with Mo catalyst
2
[41] .
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