Journal of Organic Chemistry p. 64 - 67 (1987)
Update date:2022-08-03
Topics:
Rammash, Bahlul Kh.
Wong, John L.
Cyclic imidoyl halides are assumed to undergo nucleophilic substitutions by way of addition-elimination. The imidoyl moiety in azaaldrin (1) has turned out to be a very sensitive substrate in determining the scope and limitation of the addition-elimination pathway of substitution. There was no reaction observed for 1 with 11 common nucleophiles: H, CH3, CN, SCN, SCH2Ph, S2O32-, Br-, I-, P(OR)3, ROH, H2O. This outcome was not changed by varying solvent or temperature or adding modifiers such as crown ether. However, successful substitutions of 1 and several homologues were obtained with piperidine, fluoride, thiophenolate, ethoxide, and hydroxide in alcohol. The observations are explained by applying Pearson's hard- and soft-base classification of the nucleophiles used. In general, those that are soft bases do not react with 1, while those that are hard and basic do. A mechanism is proposed that involves an early acid-base complex and a transition state stabilized by σ bonding to account for the selectivity of nucleophiles. The structure of the lactam derivative 6 is discussed in detail.
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