(b) a cyclic amine having the formula (IV) ##STR5## wherein R2 is as defined above or a salt thereof is alkylated to introduce the substituted alkyl group having the formula (V) ##STR6## by reaction with a compound having the formula R4 -Y (wherein R4 is the group having formula (V) and Y is a leaving group, for example halo such as chloro or bromo or aryl- or alkylsulphonyloxy); or