Page 89 - Catalysts for Fine Chemical Synthesis Vol 1 - Robert & Poignant

epoxidation of allylic alcohols 75

. Syringes
. Separating funnel, 250 mL
. Rotary evaporator

Procedure
1. A 50 mL two-necked flask equipped with a stirrer bar was placed in an oven
at 120 8C overnight, cooled under vacuum and flushed with nitrogen.
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2. The flask was filled with activated powdered 4 A molecular sieves (500 mg),
dry dichloromethane (40 mL) and l-(‡)-diisopropyl tartrate (400 mg).
3. The mixture was cooled to ÿ5 8C with the cooling bath, stirred and titanium
isopropoxide (297 mL) was added. After cooling the bath to ÿ20 8C, a solu-
tion of tert-butyl hydroperoxide (5.5 M in isooctane, 5.5 mL) was added and
the mixture was stirred at ÿ20 8C for 1 hour.
4. The solution of cinnamyl alcohol (2.68 g in 3 mL of dry dichloromethane)
was added dropwise over 1 hour via a syringe.
5. The reaction was monitored by TLC (eluent: petroleum ether±diethyl ether,
1:1). The visualization of the cinnamyl alcohol (UV active) with p-anisalde-
hyde dip gave a blue stain, R f 0.35, and a brown stain for the epoxycinnamyl
alcohol, R f 0.25.
6. After being stirred for 2 hours at ÿ15 8C, the reaction was quenched with
water (6 mL) and the mixture was stirred for 30 minutes at this temperature.
The solution was warmed to room temperature. Hydrolysis of the tartrate
was then effected by adding an aqueous solution of sodium hydroxide (30 %)
saturated with sodium chloride (6 mL) and stirring vigorously for 1 hour.
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7. A Bu Èchner funnel with glass frite was packed with 2 cm Celite . The two-
1
phase mixture was filtered over the pad of Celite , transferred into a
separating funnel and the organic layer was separated.
8. The aqueous phase was washed with dichloromethane (3 10 mL) and the
combined organic phases were dried (magnesium sulfate) and evaporated
under reduced pressure to afford crude product.
9. The crude material was purified by flash chromatography over silica gel
(150 g) using ethyl acetate-n-hexane (1:9) as eluent to give (2S,3S)-2,3-epoxy-
3-phenyl-1-propanol as a white solid (2.08 g, 70 %).
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The ee (92 %) was determined by HPLC analysis (Chiralpak OD column,
flow 1 mL/min, isopropanol±n-hexane; 1:9); (2R,3R)-enantiomer: R t
12.3 min, (2S,3S)-enantiomer: R t 13.4 min or by analysis of the corresponding
Mosher esters.

Derivatization with MTPA chloride
Esterification of chiral alcohols with (R)-(‡)-a-methoxy-a-(trifluoromethyl)-
phenylacetyl chloride (MTPA chloride) or its (S)-enantiomer as homochiral
auxiliaries affords the corresponding diastereoisomeric (R)- or (S)-Mosher
esters, respectively.