Cross Metathesis with Grubb's Catalyst and Enantiomerically Pure Intramolecular Metathathis of Double Bonds
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Enantiomeric purity is difficult to obtain in any chemical compound. Through methods using the enzyme known as oxynitrilase found in the bitter almond, certain a,b-unsaturated aldehydes go through the process of nucleophilic addition of HCN and form a chiral carbon with greater that 99% enantiomeric excess on the resulting cyanohydrin. If the enzyme was not used, a racemic mixture of both enantiomers would be obtained. The functional groups on the cyanohydrin are very versatile. With the correct procedure, enantiomeric purity can be preserved on the chiral carbon as the molecule is further reacted. In this paper I will discuss the formation of the cyanohydrin from the aldehyde and the formation of an a,b-unsaturated ester from the cyanohydrin. From the ester, Grubb's catalyst second Generation is used to perform a cross metathesis with multiple samples of other alkenes. Oxynitrilase is somewhat limited in the compounds that it accepts. The Grubb's catalyst is the perfect solution to this problem. The ester is made from the cyanohydrin of crotonaldehyde and the ester is then reacted with any alkene that would not be accepted by the catalyst. Specifically, the use of the Grubb's catalyst to combine the ester of crotonaldehyde cyanohydrin and 4-allyl anisole is the first integral step in the synthetic formation of the antibiotic anisomycin.