**3.3. [11C]Cyanation**

[11C]HCN is another important secondary labeling precursor (**Scheme 1**), because nitriles are not only frequently present in biologically active molecules but also represent a versatile functional group that can be readily converted into 11C-labeled amides, carboxylic acids or amines (**Scheme 7**) [54, 71]. [11C]HCN is usually prepared by the reduction of [11C]CO2 to [11C]CH4 , using H2 over nickel (400°C), and then converted into [11C]HCN by reaction with NH3 over platinum at elevated temperature (950°C) [72].

[ 11C]HCN can be used directly to form [11C]methyl-2-cyanoisonicotinate and [11C]1-succinonitrile by a Reissert-Kaufmann type reaction (**Scheme 7a**) and Michael addition (**Scheme 7b**), respectively [73]. It may convert to [11C]CuCN and react with aryl halides through the Rosenmundvon Braun reaction for the synthesis of [11C]LY2232645(**Scheme 7d**) [74–76]. 11C-labeled amino acids, for example, [11C]Sarcosine, can be prepared using [11C]HCN in the Strecker reaction (**Scheme 7c**) [51, 77, 78]. In recent years, palladium-catalyzed and copper-mediated cyanations have gained increasing attention [79–82]. Vasdev and co-workers employed arylboronic acids and [11C]CsCN to prepare aromatic 11C-nitriles (**Scheme 7f**), which was applicable to a broad range of substrates [80].
