Fluoridation of Heteroaromatic Iodonium Salts: Experimental Evidence Supporting Theoretical Prediction of the Selectivity of the Process.

Sonsoles Martín-Santamaría,^a Michael A. Carroll,^a Colm M. Carroll,^a† Charles D. Carter,^a† Victor W. Pike,^b Henry S. Rzepa,^a* David A. Widdowson,^a*

^a Department of Chemistry, Imperial College of Science, Technology and Medicine, London, SW7 2AY, UK

^b Chemistry and Engineering Group, MRC Cyclotron Unit, Imperial College School of Medicine, Hammersmith Hospital, Ducane Road, London, W12 0NN, UK

Experimental

Typical procedure for the formation of diaryliodonium tosylates: 2-(Tributylstannyl)thiophene (1.86 g, 5.0 mmol) was added to a stirred suspension of hydroxy(tosyloxy)iodobenzene—Koser’s Reagent (1.96 g, 5.0 mmol) in dichloromethane (50 ml). The resulting mixture was stirred at room temperature overnight when the solvent was removed in vacuo to give the crude product. 2-Thienyl(phenyl)iodonium tosylate was isolated as a white crystalline solid (1.85 g, 3.95 mmol, 79%); mp 155—156 ° C (from ethanol) (lit.,¹ 157—160 ° C); (Found C, 44.63; H, 3.36. C₁₇H₁₅O₃S₂I requires C, 44.55; H, 3.30.); n_max/cm^-1 (KBr) 3066, 1441, 1215, 1165, 1119, 1038, 1007, 991, 680; d_H (270 MHz; d₆-DMSO) 8.25 (2H, d, H2'/H6' J 8.0 Hz), 8.07 (1H, dd, H5 J 1.2, 3.7 Hz), 7.96 (1H, dd, H3 J 1.2, 5.4 Hz), 7.66 (1H, m, H4'), 7.44—7.52 (4H, m, H3'/H5'/H3''/H5''), 7.17 (1H, dd, H4 J 3.7, 5.4 Hz), 7.10 (2H, d, H2''/H6'' J 8.0 Hz), 2.28 (3H, s, tosylate CH₃); d_C (68 MHz; d₆-DMSO) 142.23 (C1''), 140.59 (C5), 139.64 (C4''), 135.96 (C3), 134.39 (C2'/C6'), 131.48 (C3'/C4'/C5'), 129.55 (C4), 128.60 (C2''/C6''), 125.99 (C3''/C5''), 118.78 (C2), 99.23 (C1'), 21.36 (tosylate CH₃); m/z (FAB) 288(M+H⁺, 12%), 287(M⁺, 100). [Found: M⁺, 286.9391. C₁₀H₈SI requires 286.9391].

Typical procedure for the fluoridation of iodonium salts. A suspension of caesium fluoride (30 mg, 0.2 mmol) and the iodonium salt (0.2 mmol) in acetonitrile (5 ml) was heated at 80 ° C overnight. The mixture was allowed to cool and a sample taken. The sample was filtered and analysed by GC-MS.

1 A. J. Margida and G. F. Koser, J. Org. Chem., 1984, 49, 3643.

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