Current Organic Chemistry - Volume 9, Issue 1, 2005

This review deals with the metal promoted asymmetric ring opening of achiral epoxides using achiral carbon-, nitrogen-, oxygen-, sulphur- and halogen-containing nucleophiles. The use of chiral bases in the asymmetric deprotonation of achiral epoxides yields chiral allylic alcohols. Finally, kinetic resolution of racemic epoxides can be achieved using chiral metal complexes.

Supercritical carbon dioxide is ideally suited as reaction medium for catalytic oxidations of organic substrates, and it may be exploited as one of the most promising strategies to realize some fundamental chemical transformations under environmentally benign conditions. The use of supercritical carbon dioxide as solvent for unselective hydrocarbons auto-oxidations is extensively described in the literature. Conversely, only a limited number of reports deal with selective oxidations carried out by molecular oxygen or by other primary oxidants such as hydrogen peroxide, alkyl hydroperoxides, monopersulfate, etc. In this paper recent developments in selective catalytic oxidations are reviewed and particular attention is devoted to those processes in which a metal derivative, capable of selectively oxidizing various substrates, is formed by action of a terminal oxidant such as oxygen or an organic or inorganic peroxide.

A new method of 5-chloropyrazine-2-carbonitrile preparation in a regioselective fashion and the study of the coupling of the pyrazine ring with variously substituted benzenethiols are described. A radical-ionic mechanism of this coupling, carried out in the presence of a heterogeneous copper catalyst, has been proposed. The reactivity of the substituted chloropyrazines is correlated to the calculated values of electronic deficiency in positions C(6) or C(5) or C(3) of the pyrazine ring. This nucleophilic substitution provided a series of substituted phenylsulfanylpyrazine-2- carboxylic acid derivatives. The synthetic approach, analytical and spectroscopic data of all compounds are presented.

As phosphoryl transfer reactions are ubiquitous in biological chemistry, organic chemists have been very interested in the mechanisms of phosphate and phosphinate esters. Physical organic chemistry methods, including stereochemical studies, linear free energy relationships, and, most recently, heavy-atom kinetic isotope effects, have been used in the quest for mechanistic information about the chemistry of these compounds. This review summarizes what has been learned about the uncatalyzed phosphoryl transfer reactions of phosphate and phosphinate esters.

A critical review of applications of chlorine kinetic isotope effects in studies of organic reactions mechanisms is presented. Reports from the last five years are considered. During this time chlorine kinetic isotope effects were applied mainly in studies of elimination reactions and nucleophilic substitution reactions. In several cases chemical models were also used as models of the intrinsic kinetic isotope effects in several enzymatic reactions. Both experimental and theoretical approaches have been used.