Manipulations of Carboxylation Products

Aside from standard radiation safety procedures, the methods used for the transformation of [l- C]carboxyIic acids containing more than seven carbon atoms correspond to those applied in normal organic synthetic chemistry on the same scale. But for those 

Curtius degradation of [l- C]acyl azides and [ C]carbonylation of aliphatic and aromatic primary amines have become established methods for the synthesis of [ C]isocyanates, key precursors for the preparation of labeled ureas, carbamates and thiocarbamates (see also Chapter 7, Section 7.4). Phosgene, classically the most common reagent for preparing such compounds in normal organic synthesis, is less attractive for use in carbon- 14-labeled form because it is difficult to prepare in the laboratory (see Section 5.2), it is costly to purchase. 

The utility of this approach is exemplified by the synthesis of [carbonyl- C]L-740,093 (29), a urea type CCKB antagonist, and of [carbonyl- C]EPTC 30, a thiocarbamate type herbicide. Furthermore the synthesis of 21 demonstrates that it can also be exploited 

4 Preparation of Other Building Blocks from [ CJCarbon Dioxide 

Fe203 Mo03-catalyzed oxidation of [ C]methanol with dry air 

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