Page 74 - Catalysts for Fine Chemical Synthesis Vol 1 - Robert & Poignant

epoxidation of a, b-unsaturated carbonyl compounds 59

. Acetone±distilled water (4:1), 50 mL
. Diethyl ether (50 mL), acetone (100 mL), ethyl acetate (50 mL), petroleum
ether (50 mL)

. 250 mL Round-bottomed flask with a magnetic stirrer bar
. Magnetic stirrer

Procedure

1. The N-carboxyanhydride was placed in a 250 mL round-bottomed flask
equipped with a magnetic stirrer bar, under nitrogen. Dry tetrahydrofuran
(110 mL) was then added followed by cross-linked aminomethylpolystyrene.
The mixture was stirred for 4 days.
2. The solution was filtered, diethyl ether (50 mL) was added to the solid and
collected on the filter. The solid was left to soak in the diethyl ether for 30
minutes before removing the solvent by aid of a water aspirator. This proced-
ure of soaking the solid on the filter was repeated with acetone±distilled water
(1:1), acetone±distilled water (4:1), acetone (2 50 mL), ethyl acetate (50 mL)
and petroleum ether (50 mL).
3. The white solid was placed under high vacuum overnight to give immobil-
ized poly-d-leucine (4.4 g) as a white powder.
The quality of the catalyst can be determined by performing an asym-
metric epoxidation reaction on chalcone according to the following proced-
ure. The activity of the polymer was considered satisfactory if it provided the
epoxy-chalcone in 85 % yield and 95 % of enantiomeric excess, with a reac-
tion time between 10 and 40 minutes.

4.2.3 ASYMMETRIC EPOXIDATION OF (E)-
BENZYLIDENEACETOPHENONE

H
O O
Poly-D-leucine O
UHP, DBU, THF
H
(2S,3R)

Materials and equipment
. Anhydrous tetrahydrofuran, 0.8 mL
. Chalcone (E)-benzylideneacetophenone (97 %), 50 mg, 0.24 mmol
. Poly-d-leucine, 100 mg
. Urea±hydrogen peroxide (UHP, 98 %), 27 mg, 0.28 mmol