STRUCTURES AND TROPICITY OF HYDROGENATION PRODUCTS OF A BISDEHYDRO[13]ANNULENONE AND A BISDEHYDRO[15]ANNULENONE

The catalytic partial hydrogenation of the 5,10-dimethyl-6,8-bisdehydr o[13]annulenone using Pd-BaSO4 afforded the 5,10-dimethyl[13]annulenon e together with two isomeric 5,10-dimethyl-6-dehydro[13]annulenones. T he dimethyl[13]annulenone, which is the first example of a monocyclic non-dehydro annulenone derivative larger than tropone, was found to be atropic on the basis of H-1 NMR spectra. Molecular mechanics studies indicate the extensive deviation of the molecular skeleton from planar ity and help to explain the lack of peripheral conjugation. Attempts t o obtain the [15]annulenone and the [17]annulenone from the bisdehydro [15]annulenone and the bisdehydro[17]annulenone, respectively, were un successful.