Chemistry Reference
In-Depth Information
Rh
2
(
S
-nap)
4
(2 mol %)
O
O
O O
S
S
X =
Ph
OMe
CF
3
H
2
N
HN
PhI=O, 3Å MS
CH
2
Cl
2
X
X
2
1
2
2
1
50-89% yield
56-92% ee
Scheme 4.57.
Enantioselective Rh(II) - catalyzed cyclizations of sulfonamides.
O O
O O
O O
O O
S
S
S
HN
S
HN
HN
Me
HN
MeO
2
C
HN
O
N
N
O
Me
Boc
OMe
214
215
216
217
72% yield
63% ee
98% yield
92% ee
55% yield
94% ee
87% yield
99% ee
Figure 4.17.
Examples of products from enantioselective sulfonamide cyclizations.
generally proceeded in
80% ee. More impressive examples include reactions to give
functionalized heteroaromatic substituents
214 - 217
(Fig. 4.17) with up to 99% ee [264].
The generally high levels of enantiomeric induction along with substantial functional
group tolerance shows that the work represents signifi cant progress in catalyst design
and development toward a general, highly enantio- and chemoselective amination
technology.
>
4.3.4. Intermolecular C - H Amination
The fi rst example of signifi cant levels of enantioinduction in intermolecular C- H amina-
tion was reported by Katsuki and coworkers [259,275]. The use of the highly electrophilic
cationic manganese salen complex
191
yielded C-H amination products exclusively, with
no observed aziridination (Fig. 4.18). Under optimized conditions (1,1,2,2-tetrachloro-
ethane at −40°C), a range of allylic and benzylic C-H bonds were effectively functional-
ized in 42-71% yield with moderate to high enantioselectivity (41-89% ee) [259,275].
Hashimoto and coworkers reported that a chiral dirhodium(II) carboxylate complex,
Rh
2
(
S
- TCPTTL)
4
, could effectively catalyze intermolecular C-H amination with high
enantioinduction (Scheme 4.58) [262]. An example is the amination of indane using
NsN= IPh (
185
) as the nitrene source, which afforded the product in 82% yield and in
70% ee. A variety of benzylic C-H bonds were functionalized in 52-88% yield and in
33 - 84% ee [262] .
Mueller, Dodd, Dauban, and others reported the use of the chiral tosylsulfonylimi-
damide
S
-
225
as a nitrene precursor [65,69,263]. This amination agent is very effective
and demonstrates a novel approach to increase reaction effi ciency and to avoid the use
of large excess of substrate in these transformations. In this approach, the matched reac-
