A highly diastereoselective TiCl4-mediated reduction of β-hydroxy ketones with BH3•py -: A very efficient and general synthesis of syn-1,3-diols

beta -Hydroxy ketones can be reduced to the corresponding 1,3-diols in high yields and with excellent diastereoselectivity by carrying out the reaction with BH3 . pyridine in CH2O2 at -78 degreesC in the presence of TiCl4. This protocol is general and chemoselective: excellent results are obtained when the substituents are primary, secondary, tertiary alkyl chains or aromatic moieties. The presence of reducible functionalities such as bromide, nitro and cyano groups is well tolerated.