N‐Arylation of indoles with 4‐[18F]fluoroiodobenzene: synthesis of 18F‐labelled σ2 receptor ligands for positron emission tomography (PET)

The palladium‐mediated N‐arylation of indoles with 4‐¹⁸F]fluoroiodobenzene as a novel radiolabelling method has been developed. Optimized reaction conditions were elaborated by variation of different catalyst systems (CuI/1,2‐diamines and Pd₂(dba)₃/phosphine ligands), bases and solvents in the reaction of indole with 4‐¹⁸F]fluoroiodobenzene. Optimized reaction conditions (Pd₂(dba)₃/(2‐(dicyclohexyl‐phosphino)‐2′‐(N,N‐dimethylamino)‐biphenyl, NaOBu^t, toluene, 100°C for 20 min) were applied for the synthesis of ¹⁸F‐labelled σ₂ receptor ligands ¹⁸F]‐11 and ¹⁸F]‐13 which were obtained in 91 and 84% radiochemical yields, respectively. Copyright © 2004 John Wiley & Sons, Ltd.