A one step preparation of the n.c.a. fluorine-18 labelled synthons: 4-fluorobromobenzene and 4-fluoroiodobenzene

Abstract

4-[ 18F]Fluorobromo- and [ 18F]fluoroiodobenzene are interesting precursors for organometallic nucleophilic reagents. A one-step preparation of these synthons was achieved by n.c.a. nucleophilic exchange on the corresponding 4-bromo- and 4-iodophenyl-trimethylammonium salts. The leaving ability of the trimethylammonium group increases strongly with decreasing basicity of the counter anion with the sequence: tosylate < methyl sulphate < iodide < (perchlorate) < triflate. Systematic optimization leads to radiochemical yields of 50 ± 5% and 80 ± 5% using dimethyl acetamide as a solvent within 5 min.