An Olefin Metathesis/Double Bond Isomerization Sequence Catalyzed by an In Situ Generated Ruthenium Hydride Species

Abstract

The direct conversion of allyl ethers to cyclic enol ethers using an olefin metathesis/double bond migration sequence is described. Ruthenium carbene complexes were activated to catalyze the double bond migration step by addition of hydride sources, such as NaH or NaBH4. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The Tandem Ring‐Closing Metathesis–Isomerization Approach to 6‐Deoxyglycals

“…[34] One example for this type of tandem processes is the RCM-isomerization sequence, which has been developed by Snapper et al [35] and by us. [36][37][38] In this sequence, a heterocycle is formed by ring-closing metathesis, and-after completion of the metathesis step-the metathesis catalyst is converted to an isomerization catalyst, which induces a subsequent migration of the double bond formed in the metathesis step. It turned out that this method is particularly useful for the synthesis of cyclic enol ethers, because it helps to overcome the difficulties associated with the RCM of enol ethers.…”

Ring‐Closing Metathesis in the Synthesis of Biologically Active Peptidomimetics of Apicidin A

“…The use of alternative solvents, such as toluene or 1,2-dichloroethane at reflux was unsatisfactory with low conversions, whereas THF as solvent resulted in substantial double-bond migration, possibly through the action of ruthenium hydride species, as reported by Schmidt. [14] Despite the high conversion in the cyclization of the open chain peptide 8 to its ring-closed counterpart 13, purification of the desired product from small amounts of starting material, possibly higher oligomers and catalyst by-products was hampered by its poor solubility. Indeed, all attempts at recrystallization and chromatography failed to give satisfactory yields and purities of the desired macrocyclic product.…”

Ruthenium‐Catalyzed Ring‐Closing Metathesis: Recent Advances, Limitations and Opportunities

“…Typically, C1 is converted into well-defined ruthenium hydride species (vide infra) [92] by addition of hydrogen following metathesis. An elegant illustration of the potential of assisted tandem catalysis comes from recent reports describing controlled metathesis-isomerization sequences, effected by addition of hydrogen, inorganic hydrides, or alcohol and base following metathesis [93][94][95][96]. These methodologies enable synthesis of (e.g.)…”