A method to prepare a compound of Formula Ia: or a salt of a solvate thereof, wherein: A 1a is selected from S, O or NR 2 wherein R 2 is hydrogen, C 1-6 alkyl, or C 5-12 aryl; R 1a is an R a group selected from hydrogen or C 1-4 alkyl; R 3a is an R c group which is halo; R 4a is an R d group selected from halo, C 1-4 alkylthio, or C 1-4 alkyl; and n a is an integer of 1-6; wherein said method comprises: (i) reacting in a suitable solvent a compound of Formula II: wherein: LG 1 and LG 2 are the same or different and each represents a leaving group LG; and, and m is an integer of between 1-4; with a suitable source of [ 18 F]fluoride to obtain a first crude reaction product comprising said compound of Formula II and a compound of Formula III: wherein LG 12 is a leaving group LG and p is as defined for m of Formula II; (ii) deprotonating a compound of Formula IVa: wherein R 11a, R 13a and R 14a are respectively an R a, R c and R d group as defined for Formula Ia, A 2a is an A 1a group as defined for Formula Ia, and P 1 and P 2 are each a P group selected from hydrogen or a protecting group. (iii) reacting in an alkanol solvent said first crude reaction product obtained in step (i) with said deprotonated compound obtained in step (ii) to obtain a second crude reaction product comprising said compound of Formula Ia, or a protected version thereof, wherein said crude reaction product has not been subjected to any method to isolate the desired reaction product from impurities in the crude reaction product; (iv) removing any protecting groups; and, (v) purifying said second crude reaction product to obtain purified compound of Formula Ia. A 1a is selected from S, O or NR 2 wherein R 2 is hydrogen, C 1-6 alkyl, or C 5-12 aryl; R 1a is an R a group selected from hydrogen or C 1-4 alkyl; R 3a is an R c group which is halo; R 4a is an R d group selected from halo, C 1-4 alkylthio, or C 1-4 alkyl; and n a is an integer of 1-6; (i) reacting in a suitable solvent a compound of Formula II: wherein: LG 1 and LG 2 are the same or different and each represents a leaving group LG; and, and m is an integer of between 1-4; with a suitable source of [ 18 F]fluoride to obtain a first crude reaction product comprising said compound of Formula II and a compound of Formula III: wherein LG 12 is a leaving group LG and p is as defined for m of Formula II; LG 1 and LG 2 are the same or different and each represents a leaving group LG; and, and m is an integer of between 1-4; (ii) deprotonating a compound of Formula IVa: wherein R 11a, R 13a and R 14a are respectively an R a, R c and R d group as defined for Formula Ia, A 2a is an A 1a group as defined for Formula Ia, and P 1 and P 2 are each a P group selected from hydrogen or a protecting group. (iii) reacting in an alkanol solvent said first crude reaction product obtained in step (i) with said deprotonated compound obtained in step (ii) to obtain a second crude reaction product comprising said compound of Formula Ia, or a protected version thereof, wherein said crude reaction product has not been subjected to any method to isolate the desired reaction product from impurities in the crude reaction product; (iv) removing any protecting groups; and, (v) purifying said second crude reaction product to obtain purified compound of Formula Ia.