Thiols, Selenols, and Tellurols

Abstract This chapter reviews studies into the preparation of thio-, seleno-, and telluro-car-boxylic acid esters (referred to thiol, selenol, and tellurol esters, respectively) and into their use in organic synthesis. The studies reviewed here span the last ten years, although some important and original findings reported further back than this are also included. 

Recently, Silveira and co-workers reported the synthesis of thiol, selenol and tellurol esters based on the reaction of bis(organochalcogenyl)mercury compounds with acyl chlorides in the presence of a catalytic amount of BU4NX (Eq.36) [71]. 

Reactions of Thiols, Selenols, and Tellurols.—Many of the reactions of thiols depend on the high nucleophilicity of the thiolate anion, and lead to sulphides or other sulphur-containing functional groups. Reactions of this type are therefore discussed in later sections of this Chapter. 

Preparation from Thiols, Selenols, and Tellurols.— The main methods for the synthesis of sulphides are substantially represented in the recent literature, and those papers whose topics can be clearly indicated by brief details are collected at the end of this section. 

The starting material is always the chalcogenol and, consequently, is more used for thiols than selenols and tellurols. There are several types of reactions depending if the starting materials are metal hydrides (hydrogen elimination), complexes with M C (alkane elimination), M-N (transamination), or M-O (hydrolysis) bonds. 

It has long been known that thiolate ligands (RS ), which are formally derived from thiols (RSH) by deprotonation, are well suited to form metal complexes (1). Specific reviews of this area have covered the structural chemistry of metal thiolates (la), the coordination chemistry of metal thiolates from a bioinorganic perspective (lb), transition metal thiolates (lc), and, most recently, early transition metal thiolates (Id). Because of potential thione-thiol tautomerism, a review dealing with complexes of heterocylic thione donors (le) is also relevant. This chapter concentrates on thiolate complexes of copper , lithium, and magnesium, but we also mention, for comparison or contrast, many related species of silver and gold and of some complexes that contain selenolate and tellurolate ligands. However, it should be emphasized that we have not attempted a comprehensive literature search outside the primary field of interest. 

Ending of corresponding suffixes thiol , selenol , tellurol for —SH, —SeH and —TeH, respectively. 

Scheme 6). Similarly, for seleno- and tellurocarboxylic acids, selenol and se-lenoxo, and tellurol and telluroxo forms may co-exist, respectively. Previous studies concerning the tautomerism of thiocarboxylic acids indicate that the thiol form (I) with the s-cis (syn) conformation is the predominant species. 

Syntheses of tellurol esters 3 are limited in comparison to thiol and selenol esters. A conventional preparative method is the reaction of tellurolate anions with acid chlorides or acid anhydride [113]. Co2(CO)8-mediated carbonylation of dichalcogenides (described in Sect. 3.1.10) is applicable to diphenyl ditel-luride, but the yields of tellurol esters are poor. They can also be obtained by transesterification of esters with z-Bu2AlTeBu. Reactions of tellurol esters 3 have not been extensively explored yet. However, generation of acyllithiums by Li-Te exchange is characteristic. They can be employed as acyl radical precursors in tin free radical reactions. 

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