Aryl nitrenium ions from N-alkyl-N-arylamino-diazonium precursors: synthesis and reactivity

A means of generating an N-alkyl-N-arylaminodiazonium ion, which then loses nitrogen to form a reactive aryl nitrenium intermediate, is described. In this sequence, a set of triazenyl acetonitriles was synthesized by nucleophilic addition of a nitrile anion to an aryl azide followed by temperature-dependent alkylation at either of two nucleophilic triazenyl nitrogen atoms. An alpha,alpha-disubstituted acetonitrile and N-arylaminodiazonium moiety (or aryl nitrenium ion upon loss of N-2) are embedded in the resulting 1,3,3-trisubsituted triazene, which undergoes liberation and recombination of these two components under acidic conditions to yield an alpha-arylated acetonitrile containing an all-carbon-quaternary center. We propose that the N-alkyl-N-arylaminodiazonium ion loses nitrogen to generate an aryl nitrenium species, which then reacts with an alpha,alpha-disubstituted acetonitrile either at the para- or meta-position of the aromatic ring to afford p-alkylaminoaryl acetonitrile derivatives or 3,3-substituted 1-methylindolin-2-imines, depending on the substrates and conditions.