Chemistry Reference
In-Depth Information
Chiral Ru-salen complexes and Ru-porphyrin complexes were tested for the asym-
metric aziridination [58c,59,60b]. Katsuki and others reported that Ru(salen)(CO)
complex
150
catalyzed aziridination in a highly enantioselective manner (Scheme 5.46)
[59b]. Azide compound carrying 2-(trimethylsilyl)ethanesulfonyl (SES) group was used
as a nitrene precursor, because the SES group is an easily removable
N
- protecting group
under mild conditions. The reaction of styrene
143
with SESN
3
proceeded in the pres-
ence of 1 mol % of complex
150
to give the aziridine
148
in 99% yield and 92% ee.
Aziridination of conjugated olefi n
147
also proceeded with high enantioselectivity.
NSES
Catalyst
150
CH
2
Cl
2
SESN
3
+
SES = (CH
3
)
3
SiCH
2
CH
2
SO
2
R
R
143
: R = Ph
PhC
148
: R = Ph (99%, 92% ee)
C
149
: R = (50%, >99% ee)
PhC
C
147
: R =
Ar = 3,5-Cl
2
-4-(CH
3
)
3
SiC
6
H
2
CO
N
N
Ru
O
rAA
O
Catalyst
150
Scheme 5.46.
While high levels of stereocontrol in aziridinations of olefi ns have already been
achieved, the enantiocontrol in the corresponding reaction of enol derivatives remains
elusive [60]. In general, the aziridination of enol derivatives affords α - amino ketones via
the ring-opening process of aziridine intermediates. First, asymmetric reaction of enol
acetates or silyl enol ethers using 5.5-6 mol % of chiral copper complexes was reported
by Adam and others [60a]. High enantioselectivities were reported in the amination of
silyl enol ethers with TsN=IPh in the presence of chiral Ru-salen catalyst by Che and
others [60b]. Hashimoto and others demonstrated that chiral dirhodium catalyst, Rh
2
(
S
-
TFPTTL)
4
153
, was an effi cient catalyst for the amination of silyl enol ethers (Scheme
5.47) [60c]. The reaction of silyl enol ethers
151
with NsN=IPh provided
N
- (2 -
nitrophenylsulfonyl) - α - amino ketones
152
in high yields and with enantioselectivities of
up to 95% ee. The
N
- 2 - nitrophenylsulfonyl (Ns) group is synthetically advantageous,
since the alkylation and deprotection of
N
- monosubstituted Ns - amides proceed under
mild conditions. The utility of the catalytic protocol has been demonstrated by asym-
metric formal synthesis of (− ) - metazocine.
Catalytic asymmetric aziridination of electron-defi cient olefi ns using chiral amine has
been studied by Shi and others (Scheme 5.48) [61]. The aminimide
154
was an effective
NH-transfer reagent for the aziridination of electron-defi cient olefi ns. This process
involved the
in situ
generation of a hydrazinium salt from tertiary amine and
O
- mesit-
ylenesulfonylhydroxylamine (MSH), deprotonation of the hydrazinium salt to form an
aminimide
154
, and subsequent aziridination. Treating chalcone
155
with (+) - Tr ö ger ' s
