Kinetic resolution zirconium-catalyzed

C. W. Johannes, M. S. Visser, G. S. Weatherhead, A H. Hoveyda Zr-Catalyzed Kinetic Resolution of Allylic Ethers and Mo-Catalyzed Chromene Formation in Synthesis. Enantioselective Total Synthesis of the Antihypertensive Agent (SJUUD-Nebivolol J. Am Chem Soc 1998, 120, 8340-8347. For development of the enantioselective methodology, see M. S. Visser, J. P. A. Harrity, A. H. Hoveyda Zirconium-Catalyzed Kinetic Resolution of Cyclic Allylic Ethers. An Enantioselective Route to Unsaturated Medium Ring Systems , J. Am Chem Soc 1996,118, 3779-3780. 

Hoveyda et al. reported a novel method for synthesizing of chromene 71 by ROM-RCM of cycloalkene 70 bearing the phenyl ether at the 3-position [Eq. (6.48)]." ° The yield is improved when the reaction is carried out under ethylene gas. In the case of cyclopentene 70a (n = 0) or cyclohexene 70b (n = 1), the yield is poor because the starting cycloalkene is in a state of equihbrium with the product and a thermodynamic product should be formed under these reaction conditions. They obtained enantiomeric ally pure cycloheptene derivative (5)-70e using zirconium-catalyzed kinetic resolution of 70e developed by their group, and chromene 71c was synthesized as a chiral form via ROM-RCM using lb [Eq. (6.49)] ... 

Zirconium-Catalyzed Enantioselective Carboalumination-Elimination Tandem Reaction of Allylic Derivatives and Its Application to Kinetic Resolution... 

Although mechanistically different, a successful kinetic resolution of cyclic allyl ethers has recently been achieved by zirconium catalysis [2201. Other metals such as cobalt [221], ruthenium [222], and iron [2231 have been shown to catalyze allylic alkylation reactions via metal-allyl complexes. However, their catalytic systems have not been thoroughly investigated, and the corresponding asymmetric catalytic processes have not been forthcoming. Nevertheless, increasing interest in the use of alternative metals for asymmetric alkylation will undoubtedly promote further research in this area. 

Substituted unsaturated pyrans prepared by RCM using 18 as catalyst can be immediately submitted to zirconium-catalyzed kinetic resolution of the racemic product at 70°C. This provides a new route to medicinally important agents containing 6-membered cyclic ethers. A one-pot synthesis can give 63% conversion with >99% enantiomeric purity (Morken 1994). Dienes of the type CH2=CH(CH2)30(CH2(H20) CH2)3CH=CH2 (m = 2-4) readily undergo ADMET polymerization in the presence of catalyst 8 (Qiao 1995). 

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