1,5-hydrogen transfer during diazonium ion decomposition—IV: The copper catalyzed reaction. A Case of hydrogen atom or hydride ion transfer in the same system

Abstract

Diazonium salts derived from o-amino-N,N-dialkylbenzamides have been found to undergo two discrete modes of decomposition. The thermal reaction involves a phenyl cation and yields (1) nucleophilic substitution products, (2) ring-closure products and (3) N-alkylbenzamides, which are produced along with aldehydes and ketones in a reaction involving a 1,5-hydride ion transfer. In contrast, no ring-closed products are formed in the copper catalyzed reaction. This reaction involves an intermediate phenyl radical which can (1) accept a ligand radical from a cupric salt to yield a substitution product or (2) undergo a 1,5-hydrogen atom transfer leading to a new radical which, after oxidation by cupric ion, yields the N-alkylbenzamide and the aldehyde or ketone. Either radical can abstract a hydrogen atom from an appropriate donor. This appears to be the first case in which it is possible to observe either a hydride ion or a hydrogen atom transfer in the same system. Experimental results which throw some light on the role of cuprous ions in the “copper catalyzed” diazonium ion decompositions are discussed. In this connection, cuprous oxide has been found to be extremely effective in promoting the radical decomposition of diazonium salts.