Kinetic Resolution of Alkenes

An interesting extension of this reaction is shown in the asymmetric kinetic resolution of cyclic allylic ether 44 under alkene coupling conditions. Use of (R)-12 as the catalyst gives (R)-45 in > 99% ee at 58% conversion. The ethylated product 46 is also formed in the reaction in 94% ee (Eq. 7) [25]. The reaction is effective for six- to eight-membered 3-oxacycloalkenes 47 as well as for a wide variety of alkoxycycloalkenes 48 [27], with some resolution dependency on the ring size of 47 (Fig. 2) [26]. 

Zirconocene-catalyzed kinetic resolution of dihydrofurans is also possible, as illustrated in Scheme 6.8 [18]. Unlike their six-membered ring counterparts, both of the heterocycle enantiomers react readily, albeit through distinctly different reaction pathways, to afford — with high diastereomeric and enantiomeric purities — constitutional isomers that are readily separable (the first example of parallel kinetic resolution involving an organome-tallic agent). A plausible reason for the difference in the reactivity pattern of pyrans and furans is that, in the latter class of compounds, both olefmic carbons are adjacent to a C—O bond C—Zr bond formation can take place at either end of the C—C 7T-system. The furan substrate and the (ebthi)Zr-alkene complex (R)-3 interact such that unfavorable... 

Sulfides are generally oxidized much faster than alkenes, and in the presence of excess oxidant further oxidation to the sulfone occurs. In the cases where the reaction is conducted in an asymmetric way, the chiral catalytic system may react faster with one enantiomeric sulfoxide to form the sulfone than with the other, so that kinetic resolution of the primarily formed sulfoxide may occur. In general, the reaction is carried out with alkyl hydroperoxides like TBHP in the presence of a metal catalyst like Mo, W, Ti or V complexes. In some cases the sulfoxidation with hydroperoxides can take place without the need of a metal catalyst. Both examples will be discussed in the following. 

Trisubstituted cyclic alkenes have been kinetically resolved via a chiral dioxirane (4), generated in situ from the ketone and Oxone. A sequential desymmetrization and kinetic resolution of cyclohexa-1,4-dienes has also been achieved. The observed stereochemical results have been rationalized on the basis of a spiro-planar transition state model.93... 

Fig. 3.34. Thought experiment IV kinetic resolution of a racemic chiral alkene through reaction with < 0.5 eguiv. of an...

The kinetic resolution of racemic alkenes 112 was demonstrated in asymmetric hydroboration with Rh-QUINAP catalyst. A 78% yield with 98% ee was achieved when using 0.6 equiv. of HBcat compared to the alkene.180... 

The enantiodifferentiating protonation by aminoalcohols was further utilized in the partial kinetic resolution of rrarcs-l-acetylcyclooctene (26), which is formed by irradiation of the cis cyclooctene 25 (Scheme 10) [43,44]. The trans alkene is stable in carefully dried acetonitrile. Protic species catalyze the isomerization back to the cis alkene. When the irradiation was carried out in the presence of (+ )-ephedrine, a new CD signal appeared that was assigned to the trans alkene... 

Phenols are used as the nucleophile in the asymmetric aUylation of 7r-aUylpalladium complexes. Trost and Toste attained asymmetric phenyl ether formation in high enantiomeric excess (ee) using diphosphine ligand derived from chiral 1,2-cyclohexanediamine (equation 10). Dynamic kinetic resolution of the racemic secondary aUylic carbonate is conducted in the presence of tetrabutylammonium chloride, which increases the rate of ft—a—ft isomerization of the jr-allyl palladium intermediate (equation 11). Lautens and coworkers cleaved meio-oxabicyclic alkenes with phenol in the presence of a catalytic amount of a chiral ferrocenyldiphosphine and a rhodium complex (equation 12). ... 

In 1970s, much effort was devoted to the kinetic resolution of racemic 1-alkenes (Scheme 1, an asterisk will be used throughout this article to denote optically active entities). The enantiomeric excesses, though poor, were observed in the unreacted olefins 1. The results are surprising in that the asymmetric induction occurred in simple substrates with only primitive chiral catalysts [11,12,13,14]. 

---