Reactions with Aziridines, 45. – Arene Hydrides, 5. Reversibility of Carbonyl Attack on N‐Benzoylaziridines Prior to Ring Opening by Carbanions. – Strong Influence of the Gegen Ion

A previous report had shown that anthracene hydride AH− or the xanthenyl anion X−, respectively, at first add to the carbonyl group of N‐benzoylaziridines since high yields of benzoyl dihydroanthracene 3 or benzoyl xanthene 11 were obtained when in early stages the reaction was quenched with protons. The respective intermediate carbonyl adducts 2 and 10 had been considered to be precursors of products resulting from homolysis of the aziridine ring. It is now shown that quenching of the reaction between AH− or X− and N‐benzoylaziridines 1a, b with methyl iodide or aroyl chlorides results in substantial yields of products derived from either AH− (or X−) or 1a, b. This indicates that 2 (or 10) are in equilibrium with AH− (or X−) and 1a, b. Study of the gegenion influence with X− revealed that the equilibrium concentrations of 10‐Na+ were much lower than those of 10‐Li+ while simultaneously the ring opening of 1a was distinctly faster with X−Na+ than with X−Li+. This finding suggests that, contrary to the previous assumption, the equilibrium concentrations of X− and 1a are responsible for the (homolytic) ring opening.