Abstract
The α-oxytosylation of ketones catalysed by enantioenriched iodoarenes using mCPBA as stoichiometric oxidant is reported to give useful synthetic intermediates in good yield and modest enantioselectivity. We believe this to be the first report of an enantioselective catalytic reaction involving hypervalent iodine reagents which should open up a new field for enantioselective organocatalysis of oxidation reactions.
Key words
hypervalent iodine reagents - organocatalysis - oxidation - stereoselective synthesis
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Representative Experimental Procedure
A solution of propiophenone (1 , 67 mg, 0.5 mmol) in MeCN (1 mL) was added to a solution of iodoarene 5 (15 mg, 0.05 mmol) TsOH·H2 O (285 mg, 1.5 mmol) and mCPBA (366 mg, 77% wet with H2 O, 1.5 mmol) in MeCN (2 mL) at r.t. The resulting solution was stirred at r.t. for 60 h then quenched by addition of sat. aq Na2 S2 O3 (5 mL) and sat. aq Na2 CO3 (5 mL). The mixture was extracted with EtOAc (3 × 5 mL), the combined organic layers were washed with brine (10 mL), dried over Na2 SO4 , filtered and concentrated under reduced pressure. The residue was purified by flash column chromatography (SiO2 , 80:20 hexane-EtOAc) to yield tosylate 3 (119 mg, 0.39 mmol, 78%) as a white powder. The ee was determined by HPLC on the crude and purified products: Chiracel OB-H column, 40:60 hexane-2-PrOH, 0.5 mL·min-1 , 40 °C, t
R = 18.1 min (R ), 21.6 min (S ).
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