Asymmetric reduction of a prochiral ketone chloroacetophenone

The ligand (191.4 mg) was placed in a 100 mL round-bottomed flask equipped with a magnetic stirrer bar in an oil-bath at 40 °C, under nitrogen. Dry tetrahydofuran (66 mL) was then added. After the solution turned clear, borane-methyl sulfide complex (1.32mL) was added dropwise. The mixture was stirred at this temperature for 2.5 hours. 

The crude reaction mixture was purified by flash column chromatography (10% ethyl acetate in hexane) to give the product as a colourless liquid (0.9 g, 90% yield). 

7 REDUCTION OF KETONES USING AMINO ACID ANIONS AS CATALYST AND HYDROSILANE AS OXIDANT 

Department of Chemistry, McMaster University 1280 Main St. W. Hamilton, Ontario, Canada, L8S 4M1., Phone (905) 525-9140 ext. 23483, Fax (905) 522-2509, WWW http //www.chemistry.mcmaster.ca/faculty/brook/brook.html 

One of the fundamental operations in organic synthesis remains the stereoselective reduction of carbonyl groups1241. In a process related to that reported by Hosomi et u/.[25], using hydrosilanes as the stoichiometric oxidant and amino acid anions as the catalytic source of chirality, a variety of ketones were reduced in good to excellent yield and with good stereoselectivity1261. This process reduces the amount of chiral catalyst needed and utilizes catalysts from the chiral pool that can be used directly in their commercially available form. 

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