Highly Efficient Formation of Nitriles and Alkoxy Radicals from N-Alkoxybenziminoyl Chlorides in Solution

A series of N-alkoxybenziminoyl chlorides were synthesized and reacted with tributyltin hydride in the presence of AIBN to generate the corresponding N-alkoxybenziminoyl radicals. This methodology successfully generates the desired radicals, which undergo a rapid and highly efficient β-scission reaction, as shown by the formation of the corresponding nitriles and products derived from alkoxy radicals. The intermediate N-alkoxybenziminoyl radical could not be trapped by employing high concentrations of Bu3SnH or by using a hydrogen atom donating solvent such as toluene. The fast β-scission reaction was found to be independent of the structure of the iminoyl chloride. These results are different from studies on the similar N-alkyliminoyl radicals, which typically give products from both β-scission hydrogen atom transfer pathways. Using the data from this study as well as some reported rate constants for different hydrogen atom transfer (HAT) processes, we conclude that the lower limit for the rate constant for the β-scission process (k β) in N-alkoxybenziminoyl radicals is 2.5 × 107 s−1.