Abstract
Abstract The two isomeric enol ethers of 3-methylcyclohexanone, 1-ethoxy-3-methyl-, and 1-ethoxy-5-methylcyclohexenes (5 and 6), have been hydrogenated in ethanol with six platinum group metals as catalysts. Palladium, rhodium, and platinum efficiently catalyzed the addition of ethanol to the enol ethers to give the corresponding acetal, while iridium and ruthenium catalyzed it only slightly. Osmium was moderately active for the acetal formation. Extensive isomerization between 5 and 6 occurred over all catalysts. In addition, isomerization to an allyl ether, 3-ethoxy-1-methylcyclohexene (9), was observed with 5 over the metals other than palladium. Hydrogenation of 5 and 6 with palladium gave the trans-ether predominantly. With the other metals, the cis-ether was formed in large excess from 5 and the trans-ether in slight excess from 6 at the initial stage of hydrogenation. Hydrogenolysis of the ethoxyl group occurred extensively over platinum but only slightly with palladium and ruthenium. These results are compared with those obtained with the corresponding dimethylcyclohexenes and allyl ether 9.
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