in formula i to provide the aldehyde intermediate viii the reaction may be carried out in the presence of diethyl azodicarboxylate dead or 1 1 u2032 azobis n n dimethylfornamide cf tetrahedron lett 1995 36 3789 3792 preferably dead and triphenylphosphine pph 3 in a solvent such as thf or dichloromethane mitsunobu reaction see org react 1992 42 335 656 subjecting intermediate viii to a standard reductive alkylation procedure such as described in j org chem 1996 61 3849 3862 with an appropriate amine of formula ix wherein r 5 and r 6 have the same meaning as in formula i results in a compound of this invention i when r 1 in formula i is a nitrogen protecting group as defined below the subsequent n deprotection may be performed under standard conditions such as those described in protective groups in organic synthesis john wiley amp sons 1991 to provide compounds of formula i wherein r 1 is hydrogen nitrogen protecting groups are known in the art and include those described in t w greene and p g m wuts protective groups in organic synthesis 2d ed john wiley and sons 1991 and subsequent editions thereof an obtained compound of formula i may be converted to another compound of formula i by methods well known in the art the processes described above may be carried out to give a compound of the invention in the form of a free base or as an acid addition salt a pharmaceutically acceptable acid addition salt may be obtained by dissolving the free base in a suitable organic solvent such as ether.