Conversion of ruthenium carbene complexes to ruthenium hydride complexes by organometallic transformations in situ opens up interesting synthetic perspectives. In this account the use of Grubbs' catalyst to synthesize pent-4-enals selectively from diallyl- and allyl homoallyl ethers and scope and limitations of a Tandem RCM-isomerization sequence for the synthesis of cyclic enol ethers are discussed. (c) 2006 Elsevier B.V. All rights reserved.