Chemoselective hydroxyl group transformation: an elusive target

The selective reaction of one functional group in the presence of others is not a trivial task. A noteworthy amount of research has been dedicated to the chemoselective reaction of the hydroxyl moiety. This group is prevalent in many biologically important molecules including natural products and proteins. However, targeting the hydroxyl group is difficult for many reasons including its relatively low nucleophilicity in comparison to other ubiquitous functional groups such as amines and thiols. Additionally, many of the developed chemoselective reactions cannot be used in the presence of water. Despite these complications, chemoselective transformation of the hydroxyl moiety has been utilized in the synthesis of complex natural product derivatives, the reaction of tyrosine residues in proteins, the isolation of natural products and is the mechanism of action of myriad drugs. Here, methods for selective targeting of this group, as well as applications of several devised methods, are described.

The Mitsunobu Reaction: Origin, Mechanism, Improvements, and Applications

The Mitsunobu reaction is a widely used and versatile method for the dehydrative oxidation-reduction condensation of an acid/pronucleophile usually with a primary or secondary alcohol that requires the combination of a reducing phosphine reagent together with an oxidizing azo reagent. The utility of this reaction stems from the fact that it is generally highly stereoselective and occurs with inversion of the stereochemical configuration of the alcohol starting material. Furthermore, as carboxylic acids, phenols, imides, sulfonamides, and other compounds can be used as the acid/pronucleophile, this reaction is useful for the preparation of a wide variety of functional groups. This Focus Review of the Mitsunobu reaction summarizes its origins, the current understanding of its mechanism, and recent improvements and applications.

Novel chemoselective tosylation of the alcoholic hydroxyl group of syn-alpha,beta-disubstituted beta-hydroxy carboxylic acids

[small beta]-Hydroxy acids were readily converted into [small beta]-tosyloxy acids (hydroxyl group activation) in moderate to excellent yields via the O,O-dianions generated by treatment with methyllithium and thus make it possible to prepare anti[small alpha],[small beta]-disubstituted [small beta]-lactones directly from the syn aldols.

Synthesis of α-Fluoro-β-lactones and Their Thermal Conversion to 1-Fluoroalkenes

α-Fluoro-β-lactones have been synthesized and isolated for the first time from α-fluoro-β-hydroxy acids by using the couple TsCl/DMAP as lactonization agent. A detailed description of the synthesis and spectroscopic properties of α-fluoro-β-lactones is presented. Preliminary results indicate that thermolysis of these new β-lactones produces 1-fluoroalkenes.