The present invention relates to a process for preparing a compound of formula [I], said process comprising the steps of: formula [II]+formula [III]->；formula [I] (i) forming a reaction mixture comprising (a) a compound of formula [II], (b) a compound of formula [III] and (c) 1,2-propanediol or polyethylene glycol, or a mixture thereof, and optionally (d) a base； (ii) heating said reaction mixture to a temperature of at least about 150°C to form a compound of formula [I]； (iii) isolating said compound of formula [I]； and (iv) optionally converting said compound of formula [I] into salt form； wherein: R1 and R2 are each independently H, alkyl or haloalkyl； R3 and R4 are each independently H, alkyl, haloalkyl or aryl； R5 is alkyl, alkenyl, cycloalkyl or cycloalkyl-alkyl, each of which may be optionally substituted with one or more OH groups； R6 is selected from cyclopropylamino, cyclopropylmethylamino, cyclobutylamino, cyclobutylmethylamino and formula (A) where one of X, Y and Z is N and the remainder are CR9； R7, R8 and each R9 are independently H, alkyl or haloalkyl, wherein at least one of R7, R8 and R9 is other than H. Further aspects of the invention relate to a highly diastereoselective process for the preparation of compounds of formula [III], a process for preparing intermediates of formula [II], and other intermediates useful in the synthesis of compounds of formula [I], and to a process for preparing the crystalline tartrate salt and free base of compounds of formula [I].
