The metallacyclobutane produced can then cycloeliminate to give either the original species or a new alkene and alkylidene.
Received Aug 27; Accepted Dec The license is subject to the Beilstein Journal of Organic Chemistry terms and conditions: Summary Conjugated 1,3-dienes are important building blocks in organic and polymer chemistry.
Enyne metathesis is a powerful catalytic reaction to access such structural domains. Recent advances and developments in ene—yne cross-metathesis EYCM leading to various compounds of interest and their intermediates, that can directly be transformed in tandem procedures, are reviewed in this article.
In addition, the use of bio-resourced olefinic substrates is presented.
Inthe polymerization of alkynes initiated by tungsten carbene was demonstrated by Katz [ 1 — 2 ] who proposed metallacyclobutenes as key intermediates in this polymerization. At the same period of time, Geoffroy [ 3 ] demonstrated that alkyne polymerization could be initiated directly from terminal alkynes without previous preparation of a metal carbene but via the formation of a reactive vinylidene tungsten species.
Later on, the efficiency of ruthenium vinylidene precursors was also shown in olefin metathesis [ 4 — 10 ]. It is noteworthy that polymerization of terminal alkynes [ 11 — 13 ] and cyclotrimerization of triynes [ 14 — 20 ] with ruthenium carbene precursors is still a topic of current interest.
Then, Fischer tungsten carbene complexes were used by Katz [ 21 ], and later Mori [ 22 — 23 ] utilized chromium alkoxycarbene to develop the first cyclizations via catalytic intramolecular enyne metathesis transformation.
These initial works gave reason to postulate the interaction of metal carbene with alkyne to form a metallacyclobutene that rearranges to give a metal vinylcarbene Scheme 1.
This is the mechanistic basis of intramolecular enyne metathesis and EYCM reactions.Grubbs' catalysts are a series of transition metal carbene complexes used as catalysts for olefin pfmlures.com are named after Robert H. Grubbs, the chemist who supervised their pfmlures.coml generations of the catalyst have been developed.
Grubbs' catalysts tolerate many functional groups in the alkene substrates, are air-tolerant, and are compatible with a wide range of pfmlures.comg point: °C ( °F; K) (decomposition).
Ruthenium and osmium carbene compounds that are stable in the presence of a variety of functional groups and can be used to catalyze olefin metathesis reactions on unstrained cyclic and acyclic olefins are disclosed.
Also disclosed are methods of making the carbene compounds. The carbene compounds are of the formula where M is Os or Ru; R 1 is . The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru–MIC bond to generate an extremely active metathesis catalyst.
Mechanistic studies implicated a rate-determining protonation step in the generation of . Jul 08, · Overall for this tandem reaction we propose a ruthenium carbene complex catalyzed ene–yne metathesis followed by a Diels–Alder reaction.
The syn: anti diastereomeric ratio of the isolated cycloadduct (10) of the reaction with N -phenylmaleimide is much higher when the reaction sequence is performed in the presence of ruthenium. Products and yields resulting from the metathesis of oleate-type fatty compounds in DCM at 20 °C after 4h.
Table 3. Activity and selectivity of 1 on oleate-type fatty compounds with substrate/ 1 molar ratio of in DCM after 4h. The facile synthesis of two new unsymmetrical N-heterocyclic carbene (NHC) ligands from commercially available monosubstituted diamines is presented.
The resultant unsymmetrical NHC ligands have been complexed to ruthenium to give novel olefin metathesis initiators.