The above reaction shows an epimeric steroid alcohol being converted by a catalyst of ruthenium and aluminum oxide to a racemic mixture of 17-estradiol 3-methyl ether and a ketone. The racemic mixture is formed by converting the beta version of the ether, where the hydroxyl group is on the top of the ring, to the alpha version of the ether, where the hydroxyl group is underneath the ring. The reaction is stopped when the amount of alpha ether is roughly equivalent to the amount of beta ether. In the notation used, the wavy line between the hydroxyl group and the ether shows that the hydroxyl group can be in either the front or the back of the molecule.
However, a ketone can be produced instead of the alpha ether when the alcohol is oxidized. Because the purpose of the reaction is to racemize the ether, this ketone is an unwanted side product. To prevent oxidation, toluene at 100 C is used as a solvent. The chemical properties of toluene slow the formation of the ketone so that at temperatures around 100 C, the yield of the racemic mixture is about 54%. Any ketone that does form can be separated from the ether by flash chromatography. This reaction is a good way to racemize the ether efficiently and inexpensively; it was traditionally synthesized at a much higher cost.
Amino polyols are an important part of synthetically created amino acids. They are highly antibacterial and immunosuppressive and so are used in various antibiotics and antifungal products. This reaction shows one of the step necessary in creating the amino polyol.
Benzoyl chloride is added to the polyol to form a tribenzoate compound. In this reaction, the polyol has several R-O-H groups that act as weak nucleophiles. When the benzoyl-Cl bond breaks upon addition to the pyridine solvent, the benzoyl group acts as an electrophile. With the help of the DMAP (dimethylaminopyridine) catalyst in the reaction, the R-O-H group is deprotonated and the benzoyl group is added to the remaining R-O form the final tribenzoylated product. As seen above, the reaction has a yield of about 90%. The OTBS (t-buytldimethylsiloxy) groups do not participate in this reaction.
There is one hydroxyl group left on the molecule produced. All of the hydroxyl groups would be replaced by benzoyl groups if the reaction was not stopped after three groups had been added. To stop the reaction at this point, three equivalents of benzoyl chloride were used for every polyol.
