Another process for preparing compounds according to the invention where Y is sulphur and R1 and R2 are other than hydrogen involves treatment of the amine (II) with carbon disulphide followed by reaction with a chloroformate ester e.g. ethyl chloroformate to give an isothiocyanate of formula (IX) ##STR17## When the resulting compound of formula (IX) is reacted with an amine R3 NH2, preferably in