the present invention relates to a compound of formula i wherein ar , r 1 , r 2 , r 3 , n , and o are as defined herein or to a pharmaceutically active salt , a racemic mixture , an enantiomer , an optical isomer or a tautomeric form thereof . the present compounds are high potential nk - 3 receptor antagonists for the treatment of depression , pain , psychosis , parkinson &# 39 ; s disease , schizophrenia , anxiety and attention deficit hyperactivity disorder .