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Radical-Mediated Carboxylation of Alkyl Iodides with [ 11 C]Carbon Monoxide in Solvent Mixtures

2005; American Chemical Society; Volume: 70; Issue: 6 Linguagem: Inglês

10.1021/jo047806s

1520-6904

Oleksiy Itsenko, Bengt Långström,

Chemical Reactions and Isotopes

[carboxyl-11C]Carboxylic acids were prepared from alkyl iodides via photoinitiated radical reactions using 10-8 mol of [11C]carbon monoxide in binary and ternary homogeneous solvent mixtures. Short- (isobutyric), medium-, and long-chain saturated fatty acids (heptadecanoic) were labeled with isolated decay-corrected radiochemical yields ranging from 55% to 70% in 5−7-min reactions. The conversion of [11C]carbon monoxide to products reached 80−90%. To obtain good yields in the reactions performed in water−acetonitrile and water−THF mixtures, the addition of tetrabutylammonium hydroxide or potassium hydroxide was essential. The carboxylation was efficient for primary and secondary alkyl iodides. The carboxylation of tertiary iodides was feasible for 1-iodoadamantane but not for tert-butyl iodide. The dependence of the radiochemical yields on reaction time, photoirradiation conditions, and organic and inorganic additives was studied. The method provides a one-step route to [carboxyl-11C]carboxylic acids; traditional methods, in contrast, would require several steps. For example, using the devised reaction conditions, 3.19 GBq of purified [1-11C]1,10-decanedicarboxylic acid (specific radioactivity 188 GBq/μmol) was obtained within 35 min of the end of 10 μAh bombardment. (1-13C)4-Phenylbutyric acid was synthesized using (13C)carbon monoxide for identifying the labeling position with 1H and 13C NMR.