Radical-mediated carboxylation of alkyl iodides with [11C]carbon monoxide in solvent mixtures.
[reaction: see text] [carboxyl-(11)C]Carboxylic acids were prepared from alkyl iodides via photoinitiated radical reactions using 10(-)(8) mol of [(11)C]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 [(11)C]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-(11)C]carboxylic acids; traditional methods, in contrast, would require several steps. For example, using the devised reaction conditions, 3.19 GBq of purified [1-(11)C]1,10-decanedicarboxylic acid (specific radioactivity 188 GBq/mumol) was obtained within 35 min of the end of 10 muAh bombardment. (1-(13)C)4-Phenylbutyric acid was synthesized using ((13)C)carbon monoxide for identifying the labeling position with (1)H and (13)C NMR.
Itsenko
Oleksiy
O
Department of Organic Chemistry, Institute of Chemistry, Uppsala University, Box 531, S-751 21 Uppsala, Sweden.
Långström
Bengt
B
D002248:Carbon Monoxide / Q000737:chemistry*; D002250:Carbon Radioisotopes / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry*; D006847:Hydrocarbons, Iodinated / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D012997:Solvents / Q000737:chemistry*
D002250:Carbon Radioisotopes; D005609:Free Radicals; D006847:Hydrocarbons, Iodinated; D012997:Solvents; D002248:Carbon Monoxide