Catalytic Asymmetric Olefin Metathesis

Grubbs synthesized molybdenum catalyst 74 and reported the first example of asymmetric induction by kinetic resolution of diene using RCM with complex 74. After 90% conversion of the reaction of diene with 74, an enantiomeric excess (ee) of the recovered staring material 78 showed 84% and an absolute configuration is determined to be 5  

Enantioselective cyclic ether is synthesized by molybdenum-catalyzed olefin metathesis. Cyclopentene derivative 85a is reacted with 5 mol% of chiral molybdenum catalyst 76 to give pyran derivative 86a in high yield and high ee 

Enantiomerically enriched medium-ring heterocycles are synthesized using the same protocol. Silicon or nitrogen containing heterocycle 92a or 92b is synthesized using 75a [Eqs. (6.63) and (6.64)]. Eight-membered nitrogen heterocycles 

92c can be synthesized from 91c using modified BIPOL-type complex 75c / V./ 

The catalytic enantioselective ring-closing metathesis of various polyenes affords unsaturated furans, pyrans, and siloxanes efficiently  

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Tab. 11.13 Catalytic asymmetric olefin metathesis reactions promoted by supported chiral catalyst (81). >...

For a review of asymmetric Mo-catalyzed metathesis, see Catalytic Asymmetric Olefin Metathesis, A. H. Hoveyda, R. R. ScHROCK, Chem. Eur. J. 2001, 7, 945-950 for reports on chiral Ru-based complexes, see (b) Enantioselective Ruthenium-Catalyzed Ring-Qosing Metathesis, T.J. Sei-DERS, D.W. Ward, R.H. Grubbs, Org. Lett. 2001, 3, 3225-3228 (c) A Recyclable Chiral Ru Catalyst for Enantioselective Olefin Metathesis. Efficient Catalytic Asymmetric Ring-Opening/Cross Metathesis In Air, J. J. Van Veldhuizen, S. B. 

The arena in which catalytic asymmetric olefin metathesis can have the largest impact on organic synthesis is the desymmetrization of readily accessible achiral molecules. Two examples are illustrated in Scheme 4. Treatment of achiral triene 18 with 2 mol % 4a leads to the formation of (R)-19 in 99% ee and 93% yield [ 12]. The reaction is complete within 5 min at 22 °C and, importantly, does not require a solvent. Another example is illustrated in Scheme 4 as well here, BINOL complex 11a is used to promote the formation of optically pure (R)-21 from siloxy triene 20 in nearly quantitative yield. Once again, solvent is not needed [15]. Readily accessible substrates are rapidly transformed to non-ra-cemic optically enriched molecules that are otherwise significantly more difficult to access without generating solvent waste. 

Catalytic Asymmetric Olefin Metathesis Chiral Biphen-Mo Catalysts... 

The arena in which catalytic asymmetric olefin metathesis can have the largest impact on organic synthesis is the desymmetrization of readily accessible achiral molecules. Two examples are illustrated in Scheme 4. Treatment of achiral triene 18 with 5 mol% 4a leads to... 

The molybdenum complex Mo(NAr)(CHCMe2Ph)[(3)-Me2SiBiphen] 43 was used for catalytic asymmetric olefin metathesis reactions such as desymmetrization of trienes, kinetic resolution of allylic ethers, tandem catalytic asymmetric ring-opening metathesis/cross-metathesis. Interestingly, tandem catalytic asymmetric ring-opening... 

Hoveyda, A. H., Schrock, R. R. Catalytic asymmetric olefin metathesis, in Organic Synthesis Highlights V 210-229 (VCH, Weinheim, New York, 2003). 

An area in which catalytic olefin metathesis could have a significant impact on future natural product-directed work would be the desymmetrization of achiral molecules through asymmetric RCM (ARCM) or asymmetric ROM... 

To examine the possibility of a more efficient catalytic olefin metathesis, we prepared chiral Mo-based catalysts, 4a and 4b [10]. This approach was not without precedence related chiral Mo complexes were initially synthesized in 1993 and were used to promote polymer synthesis [6]. We judged that these biphen-based complexes would be able to initiate olefin metathesis with high levels of asymmetric induction due to their rigidity and steric attributes. Chiral complexes 4a and 4b are orange solids, stable indefinitely when kept under inert atmosphere. 

The ruthenium catalysed olefin metathesis reaction is one of the most important catalytic reactions [77-79] and one that is distinctly underdeveloped for asymmetric applications [80]. Only a few concepts have been brought forward [80,81], of which the combination of a NHC ligand with a 1,1-binaphlhyl scaffold carrying a hydroxyl anchor group is the most promising to date. 

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