Organic Bases as Additives to Improve the Radiochemical Yields of [11C]Ketones Prepared by the Suzuki Coupling Reaction

Abstract

AbstractThe Suzuki cross‐coupling reaction was employed in the syntheses of eight new [11C‐carbonyl]ketones. The reactions between the corresponding boronic acids and the corresponding triflates were performed in the presence of [11C]carbon monoxide and a palladium(0) complex as the catalyst. Lithium bromide was added to facilitate the reactions, and different bases were tested to improve the radiochemical yields. All the ketones were synthesised, with the achievement of isolated radiochemical yields (decay‐corrected) of between 14 and 74%. Important improvements in the radiochemical yield were achieved by use of tetrabutylammonium fluoride in the synthesis of ketones incorporating alkyl groups, while potassium tert‐butoxide was the best base among those tested for improving the radiochemical yields in the syntheses of biaryl ketones. The optimal amount of base was determined in all cases. Only for compounds 3e and 3h were better radiochemical yields obtained when no base was used. No radiochemical impurities were detected after isolation of the compounds. The specific radioactivity for compound 3a was determined, and a value of 200 GBq/μmol was obtained. Compound 3b was labelled simultaneously with [11C] and (13C)carbon monoxide and the position of the labelled atom was determined and confirmed by 13C NMR spectrometry. Tetrabutylammonium fluoride and potassium tert‐butoxide are reported as useful bases for Suzuki carbonylation with [11C]/(13C)carbon monoxide. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)