SYNTHESIS OF [C-11] CYANOALKYLPHOSPHORANES AND THEIR USE IN THE PREPARATION OF C-11 OLEFINS

The synthesis of the C-11-labelled bifunctional precursors 3-[C-11]cyanopropylidene(triphenyl)phosphorane (1), 4-[C-11]cyanobutylidene(triphenyl)phosphorane (2). 3-[C-11]cyanopropylidene(tributyl)phosphorane (3) and 4-[C-11]cyanobutylidene(tributyl)phosphorane (4) is presented. [C-11]Cyanide was introduced in a substitution reaction with the corresponding diiodoalkane. The iodo-alkano[C-11]nitriles were then reacted with triphenylphosphine or tributylphosphine producing the labelled phosphonium salts 1'-4'. The decay-corrected radiochemical yields were 90-99% in 10-15 min. counted from the end of production oe hydrogen [C-11]cyanide. The phosphonium salts were treated with base to form the compounds 1-4. The labelled phosphoranes 1-4 were used in one-pot model reactions with some aliphatic and aromatic aldehydes, to form olefins in 47-99% decay-corrected radiochemical yield. The Z:E ratios of the olefins were determined using HPLC. Using phosphoranes 1 and 2 the Z:E ratios were 71:29-100:0. When using phosphoranes 3 and 4 the Z:E ratios were 28:72-19:81. In a C-experiment starting with 100 mCi [C-11]cyanide, one of the labelled olefins was obtained in 67% decay-corrected radiochemical yield within 55 min. The radiochemical purity of the olefin was > 98%. The position of the label confirmed by a C-11-C-13 synthesis using the same reaction pathway, and analysed by C-13 NMR spectroscopy.