Thiocarbonyl compounds structure

Beside thioamides, dithioesters are the most stable and accessible thiocarbonyl compounds. Their specific reactivity, in particular towards nucleophiUc reagents and their apphcations to the formation of carbon-carbon bonds, have already been reviewed [8]. However, as shown below, the presence of a phosphonate function alpha or beta to the thiocarbonyl group in phosphonodithioformates and phosphonodithioacetates makes these difunctional compounds very versatile building blocks. Moreover, for the phosphonodithioacetates, the substitution of the methylenic hydrogen atoms by fluorine increases again their potential as intermediates for the synthesis of modified natural and bioactive phosphorylated structures. 

Organometallic betaines of type I can be considered as the closest structural analogs of carbon betaines of the (+ )P-C-C-X( ) type (IV), which were regarded for a long time as possible intermediates in classical reactions of carbonyl and thiocarbonyl compounds with phosphorus ylides (Wittig and Corey-Chaykovsky reactions and related processes,5,6 Scheme 1). Vedejs and coworkers7,8 proved unambiguously that oxapho-sphetanes (III) are true intermediates in the reactions of nonstabilized phosphorus ylides with carbonyl compounds. The formation of oxabetaines (+)p-c-c-o(-> was detected only in the form of their adducts with lithium salts.9,10... 

TABLE 27. Structural effects on the gas-phase basicities of carbonyl and thiocarbonyl compounds X(CO)Y and X(CS)Y ... 

A direct comparison of structural effects on the GBs of carbonyl and thiocarbonyl compounds (summarized in Table 28) sets the stage for further discussions. 

Thanks to advances in computer technology, a number of theoretical studies have been performed that shed light on structural and spectroscopic properties as well as on the reactivity of thiocarbonyl compounds both in the ground and in excited electronic states. 

In this review, quantitative aspects of the structure and reactivity of these compounds are treated first. New developments in the fields of synthesis and reactivity are examined next. As a consequence of their relevance for the development of new materials23-27 and the possibilities they offer for analytical purposes, the number of studies in which thiocarbonyl compounds act as ligands of a variety of metal ions has increased in an almost explosive way. Recent reviews28-30 are also available on specific families of coordination compounds involving thiocarbonyl ligands. A concise survey of the present status of these studies is presented in the last section. 

It is fortunate that the trends of structural effects on the structures of thiocarbonyl compounds are largely basis-independent. Important examples shall be discussed later. 

The comparison of their results with data for the open-chain compounds dimethyldithio-carbonate, (CH3S)2C=0 (14)102 and dimethyltrithiocarbonate (CH3S)2C=S (15)103 sheds light on the influence of cyclation on the structure and orbital interactions of thiocarbonyl compounds. A particularly important feature is the decrease in C=0 and C=S bond lengths upon cyclation. This follows from the reduction of the S—C(sp2)—S angles... 

Thiocarbonyl compounds (e.g., compound 237) can be oxidized by m-OI-C6H4-COd I to. Y-oxidcs (sulfines, e.g., compound 238) which as 1,3-dipoles react with thioketones yielding 1,2,4-oxadithioles 239-241. The structure of the cross-product 241 was confirmed by X-ray crystallography (Scheme 76) <2005HCA2624>. 

The series of results are presented as a tabular survey with representative examples (Tables 2 and 3). When the starting thiocarbonyl compounds were not isolated but prepared in situ, their structures appear in brackets. 

Thiocarbonyl compounds react readily with diazoalkanes resulting in the formation of products containing a C-S bond such as thiadiazoles. dithiolanes and thiiranes49. The degree of stereoselectivity in such reactions strongly depends on structural factors. This can be best illustrated by the reaction of diazoethane with various methyl alkanedithiocarboxylates 1. With the exception of methyl 2,2-dimethylpropanedithiocarboxylate, this reaction affords almost quantitatively the diastereomeric thiiranes 250. 

Another example which illustrates the importance of the structure of the diazoalkane in reactions of thiocarbonyl compounds and derivatives thereof is the reaction of trithiocarbonate S,S-dioxide 6 with diazomethane and phenyldiazomethane52. Whereas the former gives the dithiolane derivative 7, the latter affords the thiirane 8. Both reactions are, however, fully stereoselective affording single diastereomeric compounds the most probable structures are depicted in the scheme. 

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