Sulfur compounds Organic Syntheses procedures

Ketenedithioacetals (1) can formally be considered as S.S-dialkylated dithioacids. However, their reactivity pattern is quite different from that displayed by compounds like dithioacids and dithioesters bearing a thiocarbonyl group, and their syntheses and properties are usually treated apart. The review by Kolb [59] and its 254 references give access to most of the literature in the field (see also [60]). a-Oxoketenedithioacetals (2) are particularly versatile compounds as three-carbon synthons in organic synthesis, and some reviews deal specifically with them [61, 62]. Many efficient procedures are available for their syntheses [59, 61], and number of these make use of the reactions of carbon disulfide with carbanionic species followed by alkylation at the sulfur atoms (see [63] and [64] for the reactions of CS2). 

Although Cr03 is soluble in some organic solvents, like tert-butyl alcohol, pyridine or acetic anhydride, its use in such solvents is limited, because of the tendency of the resulting solutions to explode.2,3 Nevertheless, acetone can safely be mixed with a solution of chromium trioxide in diluted aqueous sulfuric acid. This useful property prompted the development of the so-called Jones oxidation, in which a solution of chromium trioxide in diluted sulfuric acid is dropped on a solution of an organic compound in acetone. This reaction, first described by Jones,13 has become one of the most employed procedures for the oxidation of alcohols, and represents a seminal contribution that prompted the development of other chromium (VI) oxidants in organic synthesis. 

Several approaches have been described for the preparation of optically active sulfoxides [5-7]. The three main routes to obtain these compounds are as follows (i) the asymmetric sulfoxidation of prochiral sulfides, (ii) nucleophilic substitution using a chiral sulfur precursor, and (iii) the kinetic resolution of racemic sulfoxides. The first of tiiese methods involves the use of various oxidants and catalysts and has been the most extensively employed. There are many examples in the scientific literature and reviews are available on this approach. In recent years, much attention has been focused on the synthesis of organic sulfoxides by emplo5dng conditions compatible with the green chemistry procedures [8-10]. For this reason, mild oxidants such as molecular oxygen or hydrogen peroxide are considered in combination with novel catalysts in order to develop a mild and environmentally friendly process. 

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