Hepta-lf6-dienes disubstituted at C -4 with certain carbonyl-containing groups cyclise, in good yield, to the corresponding 4,4-disubstituted 1,2-dirnethylcyclopent-2-enes when treated with a catalytic amount of palladium acetate in chloroform containing hydrogen chloride. Changing the catalyst precursor to chlorotris(triphenylphosphine)rhodium( I ) led to the formation of the corresponding 1 -methyl-2-methylenecyclopentanes which, in turn, isomerised to 1,2-dimethylcyclopent-I -enes in ethanolic hydrogen chloride containing the rhodium complex. The effect of terminal substitution of the dienes with methyl groups was examined. 1,7-and 1,8-Dienes give rise to mixtures of five-membered ring products. Possible mechanisms for the catalytic processes are discussed. The X-ray crystal structure ana I ysis of d ic h loro (4,4d iacetyl hepta -1 6d iene) platinum ( I I ) is reported.

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Gas chromatography-mass spectrometric studies were carried out with a DP-1 mass spectrometer system (Du Pont Instruments).Spectroscopy. UV-visible spectra were recorded with a Cary-219 instrument. Emission spectra were obtained with an Aminco-Bowman spectroflurimeter.Acknowledgment. Thanks are due to Dr. J. Brummer for valuable suggestions. References and Notes(1) (a)

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