Enantioselective epoxidation of -3-methylstyrene

In an ice-cooled (0°C) 10 mL round-bottomed flask equipped with a magnetic stirrer bar were placed dry benzene (5mL), (/i)-(3-methylstyrene (118 mg) and pyrazole (30 mg) under an argon atmosphere. RuVI(L1)02] (20-40 mg) was added to the mixture with stirring. The resulting solution was stirred for overnight at 0 °C under an inert atmosphere. 

The reaction was monitored by a UV-vis spectrophotometer, and the completion of the reaction was confirmed by the disappearance of the Soret band at 442 nm. 

The mixture was passed through a silica gel column and eluted initially with petroleum ether to remove the unreacted alkene. The product epoxide was collected by using CH2CI2 as the eluent. 

The epoxide and aldehyde were identified and quantified by capillary GLC equipped with a Chiraldex G-TA column using 4-bromochloroben-zene as the internal standard (oven temp 110 °C, carrier gas He, flow rate 60-65mL min-1, split ratio 100 1, detector FID at 250 °C, (IS, 2S)-(E)- -methylstyrene oxide Rt = 6.98min (1R, 2R)-( )-(3-methylstyrene oxide Rt = 7.81 min.) The enantiopurity of the //L2R-epoxide = 70% ee, Yield = 90 % ( 99 % trans). 

A Z 2-symmetric chiral /ra/7,v-dioxoruthenium( VI) porphyrin, [RuVI(L1)02], bifa-cially encumbered by four threitol units can effect enantioselective epoxidation of (fs)- 3-methylstyrene in up to 70% ee. For the asymmetric styrene oxidation, a lower enantioselectivity of 40 % ee was obtained (c.f. 62 % ee, see Table 6.3) when 

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