Olefins asymmetric metathesis

The ruthenium-catalyzed olefin cross-metathesis to the preparation of functionalized allyl boronates has resulted in a one-pot three-component coupling procedure for the synthesis of functionalized homoallylic alcohols.617,618 The utility of the protocol was demonstrated in asymmetric allylboration using a tartrate ester (Equation (152)).617... 

Kim SG, Park TH, Kim BJ (2006) Efficient Total Synthesis of (+)-Exo-, (-)-Endo-Brevicomin and Their Derivatives via Asymmetric Organocatalysis and Olefin Cross-Metathesis. Tetrahedron Lett 47 6369... 

On the other hand, several groups have also recently developed asymmetric domino reactions through relay catalysis with combinations of organocatalysts with ruthenium catalysts. For example. You et al. demonstrated in 2009 that ruthenium catalyst could be compatible with Bronsted acid catalyst. They reported a practical and economical synthesis of chiral tetrahydropyrano[3,4-b]indols and tetrahydro-p-carbolines by the combination of ruthenium-catalysed olefin cross-metathesis and a chiral phosphoric acid-catalysed Friedel-Crafts alleviation reaction, as shown in Scheme 7.41. This domino reaction allowed the use of readily available materials to highly enantioselectively construct synthetically valuable polycyclic indole frameworks in enantioselectivity of up to 94% ee. 

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... 

Satoh T, see Miura M (2005) 14 1-20 Satoh T, see Miura M (2005) 14 55-84 Savoia D (2005) Progress in the Asymmetric Synthesis of 1,2-Diamines from Azomethine Compoimds. 15 1-58 Schmalz HG, Gotov B, Bottcher A (2004) Natmal Product Synthesis. 7 157-180 Schmidt B, Hermanns J (2004) Olefin Metathesis Directed to Organic Synthesis Principles and Applications. 13 223-267... 

A second observation was the fact that isomerization of the starting asymmetric olefin was much faster than the formation of new symmetric olefins. In fact, 40% of the initial cis olefin (Fig. 1) had isomerized to trans after only 4% conversion to new olefins. This result formally parallels the highly selective regenerative metathesis of a-olefins (60, 61), except that steric factors now prevail, because electronic effects should be minimal. Finally, the composition of the initially formed butene from r/j-4-methyl-2-pentene was essentially identical to that obtained when cA-2-pentene was used (18). When tra .v-4-methyl-2-pentene was metath-esized (Fig. 2), the composition of the initially formed butenes indicated a rather high trans specificity. 

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

Fig. 11.2 Difference in the appearance of solutions of asymmetric olefin metathesis product (97) obtained from reaction of (78a) (left) and supported catalyst (81) (right).

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. 

Asymmetric Synthesis Using a Chiral Molybdenum Catalyst In olefin metathesis, a double bond is cleaved and a double bond is formed. Thus, a chiral carbon center is not constructed in the reaction. To realize the asymmetric induction by ring-closing metathesis, there are two procedures a kinetic resolution and desym-metrization of symmetric prochiral triene. Various molybdenum complexes are synthesized in order to explore the viabihty of these approaches (Figure 6.2). 

Asymmetric Olefin Metathesis Using Ruthenium Catalysts Ruthenium catalysts for asymmetric synthesis have also been developed (Figure 6.3). 

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