Deuteration of 4-t-butyl-1-cyclohexenyl methyl ether catalyzed by platinum metals: Evidence for staggered $alpha;$beta;-diadsorbed intermediates

Deuteration of 4-t-butyl-1-cyclohexenyl methyl ether was carried out at 80 °C in cyclohexane under pressure. Over Ru, Rh, and Pd, the reaction products consisted almost entirely of the cis and trans mixtures of the corresponding saturated ethers (cis- and trans-4-t-butyl-1-cyclohexyl methyl ether), whereas over Os, Ir, and Pt, hydrogenolysis to t-butylcyclohexane was not negligible. The isomeric mixtures were separated and analyzed for isotopic distributions by mass spectrometry (MS) and for deuterium positions within each molecule by NMR spectroscopy. With most catalysts, the MS-determined isotopic distribution pattern for the cis ether was quite different from that of the trans ether. Also the NMR-based deuterium distributions were markedly different between these isomers. These dissimilarities can be best explained by assuming a few staggered αβ-diadsorbed species as intermediates in enol ether hydrogenation.