Alkenes metathesis diastereoselectivity

Tandem alkene metathesis-intramolecular Michael addition of (R)-amine 276 proceeds diastereoselectively, providing pyrrolidines 278 and 279. These pyrrolidines can be... 

Recent efforts have achieved Z-selective ruthenium carbene catalysts, providing a catalyst solution to a general problem in stereoselective alkene synthesis Diastereoselectivity in Olefin Metathesis Development of Z-Selective Ru Catalysts Vol 1, Chapter 3 Grubbs, Handbook of Metathesis, 2nd Edition, Volume 2, Chapter 7. As this is a relatively new field, mechanistic studies are... 

The origin of the diastereoselectivity of Schrock s olefin metathesis catalysts can be traced back to the preferential syn and anti conformations of the alkylidene fragment (Scheme 5.4). The steric repulsion of the alkyhdene substituents with phenoxide ligands (top row) or with imido substituents (bottom row) determines the diastereoselectivity of the alkene metathesis. 

A similar, but shorter sequence was employed in a synthesis of dihydroxanthatin, with the addition of a copper(II) salt to make the process catalytic in palladium (Scheme 6.33). ° The (3-hydride elimination terminates a sequence that includes a nucleophilic attack and an intramolecular insertion. The alkene insertion from the first t -complex 6.98 to the second t -complex 6.99 proceeds with very high diastereoselectivity. Further aspects of this synthesis, employing metathesis chemistry, can be found in Scheme 8.113. 

One important field of application of the NHC in transition metal-catalysed reactions is obviously the olefin metathesis. Among the various applications described, one can notice the nice use of complex (15) to affect the desymmetrization of oxabicyclic alkenes by a Z-diastereoselective and enantioselective ring opening/cross metathesis with enol... 

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