The present invention relates to a process for reducing a compound of formula (I) wherein X is halogen, a hydroxy group, an alkylsulfoniloxy group or an arylsulfonyloxy group; to give a compound of formula (II) as a diastereoisomerically pure compound of RS/SR configuration characterized in that said reduction is carried out by the use of (+)-B-chlorodiisopinocampheylborane or (−)-B-chlorodiisopinocampheylborane. The compounds of formula (II) are useful as intermediates for the preparation of Nebivolol.