Competing ruthenium catalyzed metathesis condensation and isomerization of allylic olefins

Catalysis at the Interface of Ruthenium Carbene and Ruthenium Hydride Chemistry: Organometallic Aspects and Applications to Organic Synthesis

“…Highly selective isomerization of allyl ethers in the presence of catalytic amounts of 4 has also been observed by Wagener et al for compounds of type 52 under conditions that are normally used to achieve acyclic diene metathesis polymerization (Scheme 12, d). [63] No double bond isomerization appears to be involved in a recently published conversion of sugar-derived oximes to nitriles that are catalyzed by first-generation Grubbs catalyst 2. For example, 54 does not cyclize to the expected RCM product under metathesis conditions; instead, formal elimination of allyl alcohol occurs to yield the nitrile 55.…”

“…While Cossy et al proposed the presence of ruthenium hydride species and, thus, a hydrometalation/β-hydride elimination pathway, as outlined in Scheme 4, [62] Wagener et al favor the π-allyl hydride mechanism, as they could not observe any metal hydride species by spectroscopic means; the metal hydride-catalyzed pathway, however, could also not be definitely excluded. [63] The isomerization of allylic alcohols to ketones, often referred to as redox isomerization, can be catalyzed by ruthenium complexes, and examples for the use of Grubbs catalyst in this transformation have been published recently. It is believed that the mechanism of this transformation in-volves replacement of a ruthenium-bound chloride ion in M by the allylic alcohol, giving intermediate N. β-Hydride elimination gives enone O, which is coordinated to a RuϪH species and undergoes subsequent migratory insertion into the RuϪH bond, leading to η 3 complex P. The complex P is cleaved from the metal by protonation to yield M and the ketone (Scheme 13).…”

Acyclic diene metathesis (ADMET) polymerization of allyl undec-10-enoate and some related esters

“…Our aim was to determine the minimum number of methylene groups that can be present in the O-alkenyl group for the polymerization to be successful using this catalyst. We wished to use catalyst 1 rather than the Grubbs ''second generation'' catalyst 2 because the latter can cause carbon-carbon double bond migration [11,12] and this could clearly cause problems in combinatorial studies.…”

“…To obtain a polymer with a DP of, say, 50 will require the formation of 49 linkages with an average yield for each one of 98% [20]. Thus, the fact that catalyst 1 has been used successfully, sometimes with only modest yields however, to metathesize, for example, allyl esters [21][22][23][24][25], allyl ethers [23,24,26,27] and allyl alcohol [11], often in cross metathesis [21,22] or RCM reactions [24][25][26] and for end-capping polymers [21,22], does not necessarily mean analogous reactions can be used successfully for polymer synthesis.…”

New selectivities from old catalysts. Occlusion of Grubbs’ catalysts in PDMS to change their reactions

“…Recently, new reactions beyond metathesis have been discovered that are catalyzed by the Grubbs' catalysts that open up new synthetic transformations. Examples of these new reactions include olefin isomerization, deprotection of tertiary amines, isomerization of allylic alcohols to ketones, Kharasch reaction, and hydrosilylation of carbonyls [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. One prominent example of a new reaction catalyzed by the Grubbs' catalysts is its transformation into an olefin isomerization catalyst.…”