Oxolanes hydrogenolysis

Hydrogenolysis of open-chain ethers is also difficult whereas cyclic ethers are much more reactive. Cyclic ethers can be classified into two groups-strained three- and four-membered rings (oxiranes and oxetanes) are sufficiently reactive to be transformed even at room temperature whereas the five- and six-membered rings (oxolanes and oxanes) undergo transformation at higher temperatures only. 

Platinum, palladium, and nickel catalysts cleave the oxolanes in the sterically less hindered position Cu is inactive toward these molecules. On supported Pt the rupture of the secondary C-0 bond was also observed [24]. Ring-opening is much easier than the hydrogenolysis of open chain ethers, presumably because of the presence of specially bonded aySy-intermediates [25], Neither on Pt nor on Ni is any difference observed between the rates of transformation of the isomers among the dimethyl derivatives of oxolanes [26]. 

---