To further elucidate the role of each reaction component under the optimized conditions, a series of omission experiments was carried out (Table ), using NBu 3 (1) as test substrate. When omitting FeCl 3 from the reaction mixture, the obtained yield drops precipitously to 37% (entry 1). When omitting both FeCl 3 and PA, only 26% of the desired product are obtained. This suggests that a non-catalyzed background reaction exists under these conditions, which contributes at 26% the overall obtained yield. Interestingly, the magnitude of this background reaction (entry 3, 26%) is similar in magnitude to the drop in yield observed when the reaction performed in the presence of BHT, an oxygen radical scavenger (73%, entry 5; yield from general condition, entry 1: 21%). These data combined suggest that 26% yield are formed via a free radical process that does not require the presence of Fe catalyst or ligand. Formation of t BuOOH 28 via hydrolysis of PhCO 3 t Bu may be responsible for the non-catalyzed background reaction, as t BuOOH has previously been reported to enable α-C-H cyanations of simple amines. This interpretation of the data is further supported by the fact that no detectable amount of product 1a is formed in the absence of the peroxyester (Table , entry 5). Finally, the importance of 18-crown-6 for increased reactivity (likely by solubilizing the cyanide nucleophile in KCN) is supported by entry 6: a significantly reduced yield (51%) is obtained in the absence of 18-crown-6. a Yields were determined by quantitative, crude 1 H NMR using 1,3-dinitrobenzene or ClH 2 CCHCl 2 as internal standard or by GC using decane as internal standard. b Butylated hydroxytoluene (2,6-Di-tert-butyl-4-methylphenol).