Development of a new sterically protecting auxiliary of the metacyclophane type and application to unsymmetrical diphosphenes, 1,3-diphosphaallene and 1,4-diphosphabutatriene

A new bulky bromobenzene of the metacyclophane type was converted to an unsymmetrically substituted 1,4-diphosphabutatriene whose spin-spin coupling constant ((3)J(PP)) turned out to be larger, for the first time, than the (2)J(PP) value of the corresponding 1,3-diphosphaallene.