Page 110 - Catalysts for Fine Chemical Synthesis Vol 1 - Robert & Poignant

96 hydrolysis, oxidation and reduction

. 50 mL Three-necked flask with magnetic stirrer bar
. Magnetic stirrer
. Glass graduated cylinders
. Two addition funnels, 10 mL
. Separating funnel, 250 mL
. Rotary evaporator
. pH-meter

Procedure

1. In a 50 mL three-necked flask with a magnetic stirrer bar was dissolved (E)-
stilbene (181 mg) in acetonitrile±dimethoxymethane (15 mL, 1/2, v/v). Buffer
(10 mL), tetrabutylammonium hydrogensulfate (15 mg) and ketone catalyst
(77.4 mg) were added with stirring.
The mixture of organic solvent and borate buffer results in a solution of
pH above 10, and with the addition of K 2 CO 3 it rarely falls below that
value.
2. The flask was equipped with two addition funnels; one of them was filled with
the solution of oxone (1 g) in aqueous Na 2 (EDTA) (4 10 ÿ4 M, 6.5 mL) and
the other one with a solution of potassium carbonate (930 mg) in distilled
water (6.5 mL). The two solutions were added dropwise as slowly as possible
over a period of 1 hour.
To maximize the conversion and enantioselectivity a steady and uniform
addition rate of oxone and K 2 CO 3 must be achieved. On a small scale
(1 mmol substrate), this is easily done with a syringe pump.
3. The reaction was monitored by TLC (eluent: n-hexane±diethyl ether, 9:1).
(E)-Stilbene was UV active, R f 0.82. The epoxide (UV active) stained blue
with p-anisaldehyde, R f 0.70.
4. After completion of the addition, the reaction was stirred for 1 hour and
immediately quenched by addition of water (10 mL) and pentane (5 mL).
5. The reaction mixture was transferred into a separating funnel and was
extracted with n-hexane (4 40 mL). The combined organic layers were
washed with brine, dried over sodium sulfate, filtered and concentrated
under reduced pressure to give a colourless oil (200 mg).
6. The crude material was purified by flash chromatography on silica gel (60 g),
buffered with 1 % of triethylamine, using n-hexane±diethyl ether (95:5) to
afford (R,R)-(E)-stilbene oxide as a colourless oil (123 mg, 0.62 mmol, 62 %).
The ee (96 %) was determined by HPLC (Chiralpak 1 AD column, flow
1 mL/min, ethanol±n-hexane; 1:9); (R,R)-enantiomer: R t 5.6 min, (S,S)-en-
antiomer: R t 10.1 min.
1
H NMR (200 MHz, CDCl 3 ): d 7.54±7.12 (m, 10H, Ph); 3.87 (s, 2H, CH).
ÿ1
IR (CHCl 3 , cm ): 3093, 3070 (C±H epoxide), 3012 (C±H aromatic), 2399,
1604, 1496, 1461, 1453 (CˆC), 1230 (C±O±C), 1071, 1028, 925, 872, 838.
Mass: calculated for C 14 H 12 O: m/z 196.08882; found [M] ‡ 196.08861.