Chemistry Reference
In-Depth Information
aqueous hydrogen peroxide as oxidant (Scheme 11.51) [86]. Although there have been
enormous numbers of effective epoxidation catalysts for different classes of olefi ns, no
catalyst had been successfully applied to cyclic enones. Ammonium salt
41
derived from
1,2-diphenyldiamine and BINOL-based phosphoric acid induces high enantioselectivity.
TFA salts of 9-amino cinchona alkaloids
42
and
43
also proved especially suitable for
the epoxidation of
β
- substituted cyclic enones.
O
O
41
or
42
•2TFA or
43
•2TFA (10 mol %)
CH
2
Cl
2
, RT, 4 h
+ 50% H
2
O
2
R
R
O
n
n
78% to >99% ee
i
Pr
i
Pr
i
Pr
OMe
NH
2
NH
2
O
O
O
N
N
P
+
−
O
NH
3
N
i
Pr
NH
2
N
OMe
i
Pr
42
43
i
Pr
41
Scheme 11.51.
Furthermore, Deng and coworkers recently discovered that cinchona alkaloid-
derived chiral diamine
42
also serves as a catalyst for enantioselective peroxidation of
α , β-unsaturated ketones [87]. Together with TBHP as nucleophile, optically active per-
oxides were preferentially obtained in high enantiomeric excesses at 23°C with small
formation of epoxides. When using more bulky hydroperoxide such as cumene hydro-
peroxide, the selective synthesis of the peroxides needs the lower reaction temperature
of 0°C (Scheme 11.52). On the other hand, complete inversion of the product selectivity
was observed at higher temperature (23 or 55°C), and chiral epoxides were provided
42
(10 mol
%)
TFA (30 mol
%)
Toluene, 0°C
cumylO
O
O
O
O
O
+ CHP
+
Ph
Ph
Ph
74%, 94% ee
86:14
42
(10 mol
%)
TFA (20 mol
%)
Toluene, 23°C
cumylO
O
O
O
O
O
+ CHP
+
Ph
Ph
Ph
1:99
88%, 97% ee
Scheme 11.52.
