THE FIRST EXAMPLE OF A TRANSOID AMIDE (IMIDE) IN AN 8-MEMBERED LACTAM

The Claisen rearrangement of the ketene aminal derived by selenoxide e limination 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 show n by X-ray crystallography to be a highly distorted transoid amide (im ide)with the largest p-orbital distortion (tau = 50.6 degrees) recorde d for a cyclic amide.