Chemistry Reference
In-Depth Information
Bisoxazoline
142
, Hg(TFA)
2
K
2
CO
3
, MeOH
CH
2
Cl
2
HO
O
O
R
O
O
138
NN
Method 1) aq KBr; LiBH
4
, Et
3
B
or
Method 2) I
2
X
O
R
Bisoxazoline
142
141
: X = H (Up to 95% ee)
139
: X = I (Up to 92% ee)
Scheme 5.44.
Catalyst
146
4-Phenylpyridine-
N
-oxide
NTs
+
TsN
IPh
Ph
Ph
145
(76%, 94% ee)
Substrate : CH
2
Cl
2
= 5:1
143
144
N
Mn
+
N
AcO
O
hPP
O
Catalyst
146
Scheme 5.45.
5.5. AZIRIDINATION OF OLEFINS
Aziridines are versatile synthetic intermediates in organic synthesis. Various asymmetric
aziridination methods have been developed for the synthesis of chiral aziridines [54].
Evans and others reported the fi rst asymmetric nitrene transfer to olefi ns catalyzed by
copper complexes bearing box ligand [55]. After this study, stereocontrol in nitrene
transfer to olefi ns has been widely investigated by using various chiral copper catalysts
[56]. The Rh-catalyzed aziridination was also studied by Müller and others in great
detail, which was extended to the asymmetric aziridination [57]. In this section, recent
topical aziridination methods are described.
Several Mn catalysts gave high enantioselectivities in aziridination of olefi ns [5] .
Catalytic asymmetric aziridination using chiral Mn-salen complex
146
has been devel-
oped by Katsuki and others (Scheme 5.45) [58a,b]. The reaction of styrene
143
with TsN= IPh
144
gave the product
145
in 76% yield and 94% ee. The presence
of catalytic amount of 4-phenylpyridine-
N
-oxide was required to obtain high
enantioselectivities.
