Kinetic asymmetric ring-closing metathesis

Figure 14.28. Kinetic resolution in the asymmetric ring-closing metathesis.

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). 

Ring-closing metathesis has been used successfully in asymmetric synthesis (Scheme 10). Chiral catalysts such as 11 can be employed for the kinetic resolution of racemates [21] (58 —> 59 -t 60). Scheme 10 demonstrates the formation of only one enantiomer 59 with a high level of optical purity. Enantiomer 60 does not undergo... 

Kinetic resolntion of cyclic allylic ethers can be performed by asymmetric Zr-catalyzed carbomagnesation. Six-, seven-or eight-membered ethers can readily be resolved by the Zr-catalyzed protocol (with ee between 81 to 99%). As an example, the tandem Zr-catalyzed kinetic resolution followed by a Ru-catalyzed ring-opening/ring-closing metathesis affords chiral chromenes with high optical purity (ee > 99%). ... 

LaDS, Alexander JB,CefaloDR,GrafDD,HoveydaAH, SchrockRR(1998) Mo-catalyzed asymmetric synthesis of dihydrofurans. Catalytic kinetic resolution and enantioselec-tive desymmetrization through ring-closing metathesis. J Am Chem Soc 120 9720-9721... 

La DS, Alexander JB, Cefalo DR, Graf DD, Hoveyda AH, Schrock RR. Mo-Catalyzed asymmetric synthesis of dihy-drofurans. Catalytic kinetic resolution and enantioselective des3fmmetrization through ring-closing metathesis. J. Am. Chem. Soc. 1998 120 9720-9721. 

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