Cross metathesis asymmetric

Hoveyda and coworkers recently developed sequential catalytic cross metathesis/asymmetric conjugate addition utilizing (4b) to make acyclic aliphatic enones (equation 31)3 Blechert developed a synthetic route toward bicyclic N-heterocycles that hinged on cross metathesis and double reductive amination to access compounds like... 

Alkyne cross metathesis Acyclic diene metathesis Asymmetric ring-closing metathesis Asymmetric ring-opening metathesis Cross metathesis... 

The significant potential of the ruthenium complex 65 was further underlined in the catalytic asymmetric ring-opening/cross metathesis of the cyclic alkene 70 (Scheme 44). This transformation is catalyzed by 5% mol of 65 at room temperature, in air, and with undistilled and nondegassed THF to deliver the corresponding diene 71 in 96% ee and 66% isolated yield. In standard conditions (distilled and degassed THF), the alkene 70 reacts in 75 min to give the diene in 95% ee and 76% yield, with only 0.5 mol % of catalyst. 

Asymmetric AUylic Alkylation acetylacetonate Asymmetric Cross-Metathesis Acyclic Diene Metathesis allyl ether... 

A similar strategy served to carry out the last step of an asymmetric synthesis of the alkaloid (—)-cryptopleurine 12. Compound 331, prepared from the known chiral starting material (l )-( )-4-(tributylstannyl)but-3-en-2-ol, underwent cross-metathesis to 332 in the presence of Grubbs second-generation catalyst. Catalytic hydrogenation of the double bond in 332 with simultaneous N-deprotection, followed by acetate saponification and cyclization under Mitsunobu conditions, gave the piperidine derivative 333, which was transformed into (—)-cryptopleurine by reaction with formaldehyde in the presence of acid (Scheme 73) <2004JOC3144>. 

The tandem use of asymmetric allylboration to give enantiomerically pure ho-moallyHc alcohols followed by cross-metathesis of homoallylic silyl ethers with p-substituted styrenes has been reported [120] (Eq. 19). Exclusively trans cross-coupled products were formed in 50-75% yields. 

During the past 2 years several research groups have published research that either uses or expands upon Crowe s acyclic cross-metathesis chemistry. The first reported application of this chemistry was in the synthesis of frans-disubstitut-ed homoallylic alcohols [30]. Cross-metathesis of styrenes with homoallylic silyl ethers 15, prepared via asymmetric allylboration and subsequent alcohol protection, gave the desired trans cross-metathesis products in moderate to good yields (Eq. 15). 

Asymmetric ring-opening cross-metathesis (AROCM), 26 922... 

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 appreciable levels of asymmetric induction observed in the catalytic ARCM reactions mentioned above suggest a high degree of enantiodifferentiation in the association of olefinic substrates and chiral complexes. This stereochemical induction may also be exploited in asymmetric ring-opening metathesis (AROM). Catalytic ROM transformations [20] offer unique and powerful methods for the preparation of complex molecules [2d, 2g]. The chiral Mo-alkyli-denes that are products of AROM reactions can be trapped either intramolecu-larly (RCM) or intermolecularly (cross metathesis, CM) to afford a range of optically enriched adducts. 

Asymmetric ring opening metathesis reactions can also be performed.67-66 In these cases, it is common for the reaction to be coupled with a cross metathesis or other reaction to avoid polymerization of the product.51 The catalysts are constantly being improved to provide higher selectivities and faster reactions. The catalyst 35 is recyclable and air-stable (Scheme 28.24).60-71... 

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... 

J. M. Berlin, S. D. Goldberg, and R. H. Grubbs, Highly Active Chiral Ruthenium Catalysts for Asymmetric Cross- and Ring-Opening Cross-Metathesis, Angew. Chem. Int. Ed. 45, 7591-7595 (2006). 

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... 

Along with better efficacy in cross metathesis, one of the areas of olefin metathesis that was awaited eagerly is the area of asymmetric olefin metathesis. As of 2000, only a few reports for evidence of asymmetric induction, all of which were catalyzed by molybdenum complexes, had been published. ... 

A later report describes AROM/CM of norbomyl alkenes and styrene coupling partners to create asymmetrically functionalized cyclopentanes with alkenyl groups that can be further elaborated. High yields (>98%) of trans (>98) cross metathesis products (predominantly the desired ring-opened, A-B metathesis product) can be achieved using (97a) (equation 22). 

Molybdenum carbene complexes. 17. 194-1 Olefin metathesis. Cross metathesis ( tZ)-a,P-unsaturated nitriles. Furthermore, era asymmetric allylboration provides fiinctionali... 

---