Highly Regioselective Ring Cleavage of N-Acylaziridines by "Anthracene Hydride" (Anion of 9,10-Dihydroanthracene). Intermediacy of a Carbonyl Adduct. Influence of Nitrogen Inversion on the Ring Opening?

Article abstract of DOI:10.1021/jo00224a060

Anthracene hydride AH^- reacts with N-acylaziridines by reductive opening of the aziridine ring and/or amidoethylation of AH^-.When the two aziridine carbons are differently substituted, in both reactions only that bond is broken which can form the more stable carbon radical quite in accord with the intermediacy of a radical anion (ketyl) 14 and with the known homolytic cleavage of 14 forming the radical 15.The extra electron in 14 is provided by AH^- being oxidized to the radical AH^., which can react with 15 either by radical combination or by hydrogen transfer.The reaction of AH^- with N-aroylaziridines can be interrupted at the stage of the carbonyl adduct 5 as is shown by the isolation of the ketones 7a,b.So, 5 (R⁴ = aryl) is considered to be in equilibrium with the radical pair AH^./14.The conversion of 5 into the final products progresses as expected from its structure apart from the observed retardation by a phenyl substituent in the aziridine ring (3a, 4a).This retardation is tentatively explained by a hypothesis assuming ring opening of 14 to occur in the transition state of nitrogen inversion.The anion X^- of xanthene resembles AH^- in its reactivity.Both carbanions react with N-sulfonylaziridines as expected from an S_N2 mechanism.