ALKENE-DIAZONIUM SALTS - NEW CHAPTER OF CLASSICAL ORGANIC-CHEMISTRY

Whereas the protonation of α‐diazo‐β‐diketones and α‐diazo‐β‐oxo esters with hydrogen chloride and antimony pentachloride yields the corresponding hydroxyalkenediazonium hexachloroantimonates, the “acid‐sensitive” α‐diazomonocarbonyl compounds can be transformed into resonance‐stabilized alkenediazonium salts by an analogous O‐alkylation with triethyloxonium hexachloroantimonate. A general route for synthesizing these compounds consists in the transformation of the p‐toluenesulfonylhydrazones of α‐halogenated aldehydes and ketones with Lewis acids. Alkenediazonium ions which are not resonance stabilized can be isolated at room temperature only if their decomposition at higher temperatures leads, via evolution of nitrogen, to vinyl cations in particularly high energy levels. Facile substitution reactions at the CC double bond with anisole and methanol demonstrate the strongly electrophilic nature of alkenediazonium salts. When electron‐donating substituments are attached to C2 of an ethylenediazonium ion, the bond order of the NN triple bond can be reduced to a level comparable with that in diazoacetic ester. Copyright © 1979 by Verlag Chemie, GmbH, Germany