Chemistry Reference
In-Depth Information
H
N
N
N
N
Ti
Ti(O
i
Pr)
4
H
2
O
OH HO
Ph Ph
O
O
CH
2
Cl
2
Ph
Ph
O
2
1
1
Ti(O
i
Pr)
4
H
2
O
H
O
O
H
N
N
N
N
Ti
O
i
Pr
Ti
O
i
Pr
O
O
O
O
Intramolecular Meerwein-Ponndorf-Verley reduction
Scheme 11.21.
The salen ligand is simplifi ed for clarity.
R
2
R
2
O
19
(1 mol
%)
R
1
*
+
30% H
2
O
2
R
1
*
R
3
CH
2
Cl
2
, RT
R
3
O
O
O
O
O
Ph
9
9
3
e
e
87%, 99% ee
(in AcOEt)
92%, >99% ee
(0.02 mol % of
21
)
75%, 95% ee
6
%
,
8
e
(in AcOEt)
Scheme 11.22.
dihydronaphthalene proceeded smoothly in the presence of only 0.02 mol % of
19
to
afford the epoxide in 92% yield with complete enantioselectivity. It is of note that the
reaction is stereospecifi c and that an acyclic
cis -
substituted olefi n underwent epoxidation
to give the corresponding
cis
-epoxide as a sole product. While dichloromethane is the
best solvent, more environmentally friendly ethyl acetate is also available as a solvent
without loss of the enantioselectivity.
The remarkable catalysis of complex
19
can be recognized in the results obtained
with aliphatic olefi ns, which are the most challenging substrates for asymmetric olefi n
epoxidation, due to their inherently low reactivity toward electrophilic oxidant and
the diffi culty in their enantioface differentiation (Scheme 11.23) [38]. A variety of
