CATALYTIC FORMATION OF CONJUGATED DIENONES FROM YNONES BY A RUTHENIUM COMPLEX

A type of isomerization is described in which ynones are converted into conjugated dienones. The reaction was catalyzed by a ruthenium-triphenylphospine complex, RuCl2(PPh3)3, in refluxing acetonitrile. CoCl2(PPh3)2 was moderately active as the catalyst, whereas RhCl(PPh3)3 and PdCl2(PPh3)2 were much less active. It is noteworthy that the reaction could be performed in air. Results are summarized. Both aromatic and aliphatic alkynyl ketones took part in the reaction, aliphatic ones requiring longer reaction times to achieve reasonable yields. Alkynyl amide was totally unreactive. The dienones formed had predominantly E, E configuration deduced from the H NMR spectra. Usually a small amount of an isomer was also produced (not more than 8% of the main product). Simple alkynes, e.g. 1-octyne, did not participate in the isomerization. The yield of the dienones decreased considerably with decreasing catalyst concentration.