The pinacol rearrangement is essentially a dehydration reaction of an alcohol, specifically a diol. The following is an example of a pinacol rearrangement in which the (R,R)-diol (TBDMS is tert-butyldimethylsilyl) was allowed to react with 2,2 dimethylpropane (2,2-DMP) in the presence of boron trifluoride etherate at room temperature. This particular reaction was done in order to attain the acetone derivative.
Interestingly, instead of retaining its chirality, the product of the pinacol arrangement actually resulted in a racemic mixture. Subsequent derivatives of this product eventually yield benzophenone (hydroxyphenstatin), which, biologically, is a potent antitumor and antimitotic agent. Accordingly, hydroxyphenstatin has also been proven to inhibit tubulin assembly.
The reaction shown above outlines the synthesis of the lupinine ester. These esters have been studied for their biological properties. Found mainly in plants there is heavy research being done on them for their antiviral, antitumor and hepatoprotective activity. In some cases lupinine esters can exhibit local anesthetic properties.
The reaction shows how you would synthesize a lupinine ester from betulonic acid chloride with lupinine. Side conditions for this reaction include the presence of triethylamine and must be performed in dry CCl4.
Methyl 3-, 6- and 13-oxo tetradecanoates went through reduction with NaBH4 in the presence of 1,2:5,6-di-O-isopropylidene-Dglucofuranose (DIPGH) and menthol together with isovaleric and pivalic acids in THF solution. This work signifies the importance of positional
effect. The position of lower steric hinderance and higher enantiomeric excess and asymmetric reduction yield were noted down, namely the prochiral 13-keto isomer structures.
With this asymmetric reduction at normal atmospheric pressure together with inexpensive auxiliaries make it competitive with other reduction methods and is needed to assess the need in the market.
The above is one of the final reactions in the synthesis of an enantiospecifically labeled fatty acid. It involves a reduction with Lindlar’s Catalyst in the presence of deuterium, an isotope of hydrogen. Lindlar’s Catalyst (powdered barium sulfate coated with Pd, poisoned with quinoline) converts an alkyne to a cis-alkene, as seen in the reaction above. The article I looked at focused on pheromone biosynthesis in S. isatideus and the role stereochemistry played.
The main protocol for the synthesis of β-alkoxy alcohols is the alcoholysis of 1,2-epoxides. To synthesize epoxides, we can use oxone in the presence of transition metal complexes, or cyclodextrines, or via the formation of dioxiranes.
An application of this type of reaction is the synthesis of β-methoxy alcohols. It is done by the one-pot reaction of alkenes with oxone in methanol without any other catalyst.
Note: Oxone (2KHSO5·KHSO4·K2SO4) is the registered trademark from Du Pont.
General reaction and some examples are shown above.
