Thiocarboxylate Derivatives

Macor has developed what appears to be a quite general method for the acylation (protection) of the indole nitrogen using l,r-carbonyldiimidazole (CDI) in the presence of DMAP. Reaction of substituted indoles 98 with CDI presumably occurs to form the imidazolyl amide of indole 99 which upon treatment in situ with either amines, alcohols or thiols affords the desired indole-1-carboxamides, -1-carboxylates, or 1-thiocarboxylates derivatives 100, respectively. 

RU,S5-[(CpFe(CO)(PPha)(COCH2))2CH2]. The synthesis and structure of [PPN][BiCl2(Fe(CO)aCp)2] has been reported as an example of an anionic 4-coordlnate 10-electron bismuth complex.A series of new half-sandwich iron thiocarboxylate derivatives [FeCp (CO)(EPha)(SCOR)] have been prepared emd characterized through photolytic CO substitution reactions ... 

Thiophenyl acetates (366 R = Me) and propionates (366 R = Et) react with electrogenerated polysulflde ions S3 in DMF to yield thiocarboxylate ions, thiolate ions, and phenyl tetrasulfanide (367), the last deriving from the reaction of thiolate ions with sulfur (Scheme 48). Smdies of the aminolysis by a set of substimted anilines of Y-aryl dithio-2-thiophenates (368 X = S) and dithio-2-furoates (368 X = O) in acetonitrile have shown that the rate-determining step in these reactions is the departure of the thiophenolate ion from the zwitterionic tetrahedral intermediate T= = (Scheme 49). Experiments with deuteriated anilines yielded k i/IcQ values of 1.7-1.9,... 

S,3R). Secondly, the t/treo-3-methyl-D-cysteine (25,35) was prepared using the previously described addition of thiocarboxylic acid to threonine-derived aziridines. 62 ... 

Tominaga et al.1B0 studied the cycloaddition of DMAD to 3-indoledi-thiocarboxylic acid derivatives (278). A 2-substituent was essential for success, and 278 (R1 = R2 = R3 = Me) gave a 90% yield of 279. Similarly, morpholino- and piperidinothioamides 282 formed cycloadducts 283. Treatment of 279 with methanolic hydrochloric acid gave 281 via the ring-cleaved intermediate 280. 

Coupling sodium tellurocarboxylates with R SiCl gives the unstable silyl derivative which isomerizes to the more thermodynamically stable RC(Te)OSiR 3 through a facile rearrangement that can be readily followed by 13C NMR spectroscopy. This contrasts with the reaction of alkali metal thiocarboxylates which give the O-silyl ester directly. There is no evidence for the S-silyl intermediate101. 

Both Bu3SnH and (Me3Si)3SiH are able to reduce alkyl iodides or bromides but not alcohols. However, in the Barton-McCombie reaction, they reduce certain alcohol derivatives, namely, ones that contain a C=S double bond (e. g., thiocarboxylic esters or thiocarbonic esters). Figure 1.39 shows how the OH group of cholesterol can he removed by means of a Barton-McCombie reaction. The C=S-containing alcohol derivative used there is a xanthate. 

Nucleophilic attack of ammonia or of a primary or secondary amine on an O-alkyl thiocarboxylate (2) provides a formally straightforward approach to thioamides and a number of examples have been reported (equation l). - However, some limitations should be noted. Thus, there is a tendency of esters (2) to rearrange to their 5-alkyl isomers on heating (cf. Volume 6, Chapter 2.5) and these yield amides with amines rather than thioamides. Besides, excess primary amine will lead to amidine formation, or the tetrahedral intermediate of the substitution reaction may break down to an imidate rather than a thioamide (cf. Volume 6, Chapter 2.7). These unwanted side reactions are favoured in polar, protic solvents such as ethanol. In contrast, THF has proven to be particularly useful in the synthesis of tertiary thioamides according to equation (1). For improved reactivity in the preparation of V-aryl derivatives and milder reaction conditions, it is advantageous to employ the amine in the form of its Mg salt. ... 

Acylation of a simple thiol with an alkyl carboxylate is not a very suitable method for preparation of S-alkyl thiocarboxylates. Transesterification is, however, possible if either the thiol or the carboxylic ester is activated. The enhanced reactivity of boron, aluminum and silicon thiolates has been utilized for the synthesis of a large variety of thiocarboxylic S-esters, including hydroxy derivatives (from lactones). a,P-Unsaturated thiol esters, e.g. cinnamoyl or 2-butenoyl derivatives, are also accessible. Michael addition, an undesirable side reaction of thiols, is completely avoided if alkyl trimethylsilyl sulfides ortris(arylthio)boranes are applied. ... 

Pyrido[2,3-b]-l,4-thiazepines were assumed to be unstable intermediates in the reaction of lithiated 2-chloro-3-cycloalkylidenaminopyridines with O-ethyl thiocarboxylates, yielding 1,5-naphthyridine derivatives after extrusion of sulfur (93S1227). 

TABLE XXXIV. 3-Pyrazolin-o-oneB. Carboxylic Acids and Thiocarboxylic Acids and Derivatives... 

Cyclic ethers, notably epoxides (equation 12), and lactones are readily ring opened by thiosilanes through C-O bond cleavage to give the siloxy derivative (equation 13)13. Thiosilanes, both linear and cyclic, substitute ketals (equation 14) and insert fluoro-ketones and chloral across the Si-S bond (equation 15)14. With readily enolizable ketones, the enol ether results, a-bromoacetophenone is substituted, and acyl chlorides give thiocarboxylates (equation 16)15. 

S-Methyl thiocarboxylates. Ketene S,S-dimethylacetals (1) can be hydrolyzed to S-methyl thiocarboxylates (2) by trifluoroacetic acid in water. Ketene thioacetals derived from 1,3-dithiane are unchanged by this procedure. ... 

---