Reactions of Alkenediazonium Salts. Part 1. 2,2‐Diethoxyethene‐diazonium hexachloroantimonate: A diazonium, a carbenium or an oxonium salt?

Abstract

AbstractReactions of the title compound 1 with various nucleophiles have been studied. The salt behaves like an alkylating agent towards ethers, alcohols and water forming ethyl diazoacetate (2), which reacts further with excess of the nucleophile. A solvent cage mechanism accounting for the observed products is proposed. Thermal decomposition in inert solvents leads to the alkylation of the counter‐ion, i.e. formation of chloroethane, and in anisole, alkylation and chlorination of the solvent are also observed.With a standard coupling component, 2‐naphtholate ion, no azo coupling reaction of 1 is observed, but instead 14‐methyl‐14 H‐dibenzo[a,j]xanthene (17) is formed. The products of the reaction with diethylamine are diethylcyanoformamide (18) and ethyl diethylcarbamate (19). None of the chemistry of salt 1 is explained by the intervention of vinyl cations expected to be formed in a heteroytic dediazoniation. The predominant pathways seem to involve reactions of an oxonium salt (alkylating properties) or, in the case of diethylamine, a carbenium salt (primary nucleophilic attack on the β‐C‐atom of 1).The free energy barrier to CC rotation in 1 is estimated to be 75 to 77 kJ/mol (18.0 to 18.5 kcal/mol), a value which falls between those expected for a double and a single bond.