Complex-Base-Promoted Syn Eliminations from trans-1-Bromo-2-chlorocyclohexane

Article abstract of DOI:10.1021/jo00154a025

Syn eliminations from trans-1-bromo-2-chlorocyclohexane (1) induced by complex-base combinations of NaNH2-NaOR(Ar) in tetrahydrofuran at room temperature favor dehydrochlorination (54-65percent) over dehydrobromination.Under the heterogeneous reaction conditions, oxyanion bases derived from tertiary, secondary, and branched primary alcohols as well as phenols and 2-butanone are effective complex-base components, which suggests that NaNH2 is the effective base species.Reactions of 1 with NaNH2-Na-t-Bu are not influenced by ultrasonic irradiation, but the propensity for lossof the normally poorer leaving group disappears in the presence of 15-crown-5.Transition states for complex-base-promoted syn eliminations are discussed.