Tau pet imaging ligands

A process for the preparation of a compound according to Formula (I′),

• wherein either R1 is 18F and R3 is H, or R1 is H and R3 is 18F;
• or R1 and R3 are both H, and R2 is selected from the group consisting of —C1-4alkyl-18F, —OC1-4alkyl-18F, and —NR4—C1-4alkyl-18F, wherein R4 is H or methyl;
• the method comprising reacting (a) a compound of Formula (P-a1) or (b) a compound of Formula (P-a2), or a pharmaceutically acceptable salt or a solvate thereof, with a source of fluoride 18F−, or (c) a compound of Formula (P-b1) or (d) a compound of Formula (P-b2) or (e) a compound of Formula (P-b3), or a pharmaceutically acceptable salt or a solvate thereof, with an activating reagent in the presence of a base to obtain an activated compound, and subsequently reacting the resulting activated compound with a source of fluoride 18F−
• wherein the activating reagent is methanesulfonyl chloride or 4-toluenesulfonyl chloride.

A compound according to Formula (P-1)

• wherein
• R2 is methyl, and either R is selected from the group consisting of Br, —NO2, —[N(CH3)3]+, and 4-CH3-Ph-SO2—O—, and R3 is H, or R1 is H and R3 is selected from the group consisting of Br, —NO2, —[N(CH3)3]+, and 4-CH3-Ph-SO2—O—;
• or
• R1 and R3 are both H, and R2 is selected from the group consisting of —C1-4alkyl-Br, —C1-4alkyl-I, —C1-4alkyl-O—SO2CH3, 4-CH3-Ph-SO2—O—C1-4alkyl-, —C1-4alkyl-OH, —OC1-4alkyl-Br, —OC1-4alkyl-I, —OC1-4alkyl-O—SO2CH3, 4-CH3-Ph-SO2—O—C1-4alkyl-O—, —OC1-4alkyl-OH, —NR4—C1-4alkyl-Br, —NR4—C1-4alkyl-I, —NR4—C1-4alkyl-O—SO2CH3, 4-CH3-Ph-SO2—O—C1-4alkyl-NR4—, and —NR4—C1-4alkyl-OH, wherein R4 is H or methyl;
• or a pharmaceutically acceptable salt or a solvate thereof.