Process for the preparation of a compound of formula (I) as defined herein by (i) triflating a ketone of formula (II) as defined herein to form a triflate of formula (III) as defined herein and (ii) reacting the compound of the formula (III) to form a compound of the formula (I) or a pharmaceutically-acceptable salt thereof. The triflating step is conducted in the presence of a base comprising a tertiary or heterocyclic amine such that the pKa of the conjugate acid at 25° C. is within the range 5.21 to 12. The base is selected from pyridine, 2,6-lutidine, N-methylmorpholine, 1,4-diazabicyclo[2.2.2]octane (DABCO), trimethylamine, triethylamine, N,N-diisopropylethylamine (DIPEA), quinuclidine and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).