The first example of a transoid amide (imide) in an eight-membered lactam

Abstract

The Claisen rearrangement of the ketene aminal derived by selenoxide elimination of the seleno-aminal 1 in refluxing toluene in the presence of dihydropyran yields the expected unsaturated eight-membered lactam derivative 3, as well as two unexpected products 7a and 7b; the major product 7a(resulting from a selenium re-addition reaction) was shown by X-ray crystallography to be a highly distorted transoid amide (imide) with the largest p-orbital distortion (τ= 50.6°) recorded for a cyclic amide.