Mini-Reviews in Organic Chemistry - Volume 3, Issue 1, 2006

Several classes of chiral ligands have been largely used to increase the enantioselectivity of asymmetric Reformatsky reaction, however, chiral diamines and aminoalcohols ligands generally shown better results. Hence, this review describes the results using chiral ligands in the very important Reformatsky reaction.

The redox equilibrium between alcohol - carbonyl groups is greatly used by enzymes and chemists to prepare useful compounds. Carbonyls are often intermediate groups whose reactivity can be used to synthesize complex structures; in contrast, alcohols are more easily found in the products of interest because their coordinative ability is used both in biology and in chemistry. Dehydrogenase activities are an interesting alternative to chemical redox reactants because they are often chemo-, regio-, and stereo-selective. These enzymes allow for two different uses: direct, as racemates resolving agents; inverse, as enantioselective reducing agents. We will focus on their use as oxidative agents, considering both the well-known alcohol dehydrogenases and the less known and less used 1,2-diol dehydrogenases. An account of both classes will be presented.

This review describes recent developments in the homolytic ring opening of epoxides mediated and catalysed by titanocene(III) complexes, with special emphasis on their applications for the synthesis of natural products.

Chiral alcohols are useful intermediates and auxiliaries in organic synthesis. Their preparation in enantiopure form is consequently of very high interest. Among the different enzymatic procedures, the use of dehydrogenase activities can be considered as the most attractive alternative. These enzymes can fruitfully work in inverse direction as enantioselective reducing agents. We will focus on the use of well-known alcohol dehydrogenases, describing their application in chiral alcohol preparation. A final discussion on the possibility of using these enzymes in either oxidative or reductive direction will be presented.

Epothilones are natural products present in the myxobacterium Sorangium cellulossum strain 90. Due to their antitumoral activity, they are good candidates for the treatment of various forms of cancer, and epothilones B and D and some synthetic analogs are actually under advanced clinical trials. This review describes the synthesis of epothilones A and B and some of their analogs.

In the recent years, in addition to the more traditional methods based on X-ray diffraction and mechanistic considerations, the problem of the configurational assignment of optically active sulfoxides has been approached with spectroscopic methods. In this review the methods based on the use of NMR spectroscopy and electronic circular dichroism are described, as well as the emerging approaches based on the analysis of vibrational CD spectra, on the ab initio calculation of the optical rotation and on the cholesteric induction in nematic solvents. The advantage and limitations of each approach are discussed with a major attention to their reliability and practicality.