Thionation methods

Perlmutter and coworkers reported an improved reaction of amides 45 with solid-supported P2S5 reagent in tetrahydrofuran (TH F) at 60 °C under microwave irradiation to generate 11 new thioamide derivatives 46 in 76-92% yields (Scheme 12.17). Compared to that with conventional heating, the reaction time is significantly reduced by microwave irradiation. Besides the shortened reaction periods, this thionation method also allowed more convenient workup procedure [38]. 

Dithio-squaraines 37 can be synthesized via thionation of the correspondent oxo-squaraines 5 with phosphor pentasulphide or Lawesson reagent (Fig. 8) [103, 104], However, dithio-squaraines containing carboxylic groups cannot be obtained by this method. Symmetrical indolenine- and benzothiazole-based monothio- (38) and dithio- (37) squaraines containing carboxy and sulfo groups are synthesized using 1,2-dithio- and tetrathiosquaric acid, respectively, while the reaction of these... 

The conversion of a carbonyl to a thiocarbonyl group, or thionation , is a common procedure for the synthesis of thioketones. Several methods that use P4Sio,49 51 Lawesson s reagent (L.R.),2 52 57 H2S,58 59 NaHS,60 or hex-amethyldisilathiane (HMDST)61,62 are described. L.R. and P4S10 have been used to sulfurate partially and entirely perfluorinated carbonyl compounds,63 which are then trapped as anthracene adducts in a one-pot reaction. H2S has... 

Scheme 12 shows synthesis of 1,2,3-thiadiazoles by the Wolff, Hurd-Mori and Pechmann-Nold methods. Pechmann s and Wolffs are the oldest of the methods. The Pechmann-Nold synthesis involves the [3 + 2] cycloaddition of diazo-compounds to isothiocyanates or thiocarbonyl compounds (modified Pechmann synthesis). The use of thiocarbonyl compounds in the [3 + 2] cycloaddition step has broadened the scope of this reaction and made the starting materials more readily accessible. Wolffs method requires the synthesis of diazoketones that are treated with a thionating reagent to produce 1,2,3-thiadiazoles. With the development of new methods of diazotransfer reactions, the diazoketone precursors have become easily attainable and with further attention to the thionating reagents, this reaction is also useful for the synthesis of 1,2,3-thiadiazoles. 

These methods are limited in scope. Direct thiation has been reported for the transformation of vicinal diketones to [3,4]-annelated thiophenes <1996CHEC-II(7)49>. Thionations and selenations of vicinal halomethyl ketones with thioacetamide or iV,iV-diethylselenopropionamide as sulfur and selenium donors, respectively, have also been reported <1996CHEC-II(7)49>. In a recent example, thieno[3,4-f]pyrazoles 160 were readily prepared from aryl 5-bromomethyl-l//-l-phenylpyrazole-4-yl ketones 159 by reaction with thioacetamide (Equation 35) <1998JHC71>. Additionally, an example of an amination cyclization by reaction of 161 with benzylamine to afford pyrrolo[3,4-i/ thiazole 162 has been described (Equation 36) <1998JHC71>. 

More recently Christiansen 4 has made a careful study of the polythionic acids and especially of certain physical properties—K-radiations, electrical moments, and molecular weights by ebuHioscopic methods—of the p-toluoyl-tri-, -penta- and -hexa-thionates, and suggests that none of the foregoing formulae is adequate, but that the properties and reactions of the acids are best explained by the assumption that the... 

The H2S/HC1 method of thionation of ketones was efficiently applied in the syntheses of aromatic thioketones, such as thiobenzophenone [129] and hindered aliphatic thiones, e.g. thiocamphor [128, 130] and thiofenchone [128, 131]. The following convenient procedure uses trimethyl orthoformate as a co-reactant [128]. 

More stable than many other thiocarbonyl compounds, thioamides have been known and used for a long time. Reliable methods of synthesis [119] were introduced as early as 1815 by Gay-Lussac for the reaction of nitriles with hydrogen sulfide and 1878 by Hoffman for the thionation of amides by means of tetraphosphorus decasulfide. 

For simpler, less hindered aliphatic thioketones, the method of Mayer and Berthold [132] of thionation of acetals by H2S was shown [133] to lead to tautomerically pure thioketones when the transformation was carried out under sufficiently mild conditions. Thus the reaction at 0°C in ethanol or THF in the presence of 0.05-0.01 eq of zinc chloride yielded reasonable yields of thioketones (2) devoid of the isomeric enethiols (2 ). 

There are some general synthetic routes to isothiocyanates [182]. One of the most straightforward methods is the selenium-catalysed thionation of isocyanides by elemental sulfur [183],... 

N-AUcylthiolactams.2 N-Alkyllactamscan be converted into N-alkylthiolactams by the same method previously used to convert lactones into thiolactones (10, 417). However, the method is not applicable to thionation of acyclic N,N-disubstituted amides [RC(S)OR is obtained instead]. 

The metabolic and/or hydrolytic products of parathion encountered as residues in the urine include both diethyl phosphoric acid and diethyl phosphorothioic acid, most probably as their salts (potassium or sodium). Derivatization of these residues with diazomethane would result in the formation of three trialkyl phosphate compounds, namely, 0,0-diethyl O-methyl phosphate (DEMMP), 0,0-diethyl 0-methyl phosphoro-thionate (DEMMTP), and 0,0-diethyl S-methyl phosphorothiolate (DEMMPTh). Earlier (15), it had been shown by combined gas chromatography-mass spectrometry and other analytical data that a later-eluting major product ca. 85%) of the methylation of diethyl phosphorothioic acid formed under the conditions of the analytical method was DEMMPTh, and the minor product formed (ca. 15%) was DEMMTP. Accordingly, all three trialkyl phosphates were observed and confirmed by mass spectrometry in the analysis of the human urine extract. Sufficient internal bond energy differences are associated with the isomeric structures DEMMPTh and DEMMTP that qualitatively and quantitatively dissimilar fragmentation patterns are observed for both isomers as can be seen from the mass spectra of these compounds shown in Figure 4. 

Alternatively, for A -monosubstituted thioamides, methods based on nucleophilic addition of hydride, carbanions, or cyanide to isothiocyanates are available, and, quite often, thionation of the corresponding amides provides a convenient route to thioamides (c/. Volume 6, Chapters 4.1 and 4.3). ... 

Dimercapto-l,3-dithiol-2-thionate was proposed for the determination of copper in metallic alloy [17]. The absorbance was measured at 430 nm ( e = 9.06 10 1 mol cm ). A comparative study with a method using cuproin showed good agreement. 

This method involving [4+1] units (Figure 5) is exemplified by a C3S unit reacting with a sulfur source. The thionation of l,l-bis(alkylthio)alkene-3-ones or 3-ketoacids is widely used in the preparation of l,2-dithiole-3-thiones (Scheme 17) and can be used for many structural types <82AHC(3i)63, 89JAP(K)01319478, 93MIP 311-01 >. It has also been applied to a dithiolodithiole (127)... 

Starch thiols can have the SH group directly on the pyranose ring or in a side chain. There are several methods of synthesizing starch thiols of the first type. One of them is based on the pyrolysis of starch xanthates (32), but the reaction proceeds in two parallel routes one producing thionates (35) and the other producing thiols (37).2675,2677 Reduction of starch xanthates with NaBPU in alkali is another approach to thiols. Thiols prepared in this manner were subjected to graft polymerization with vinyl polymers. Nucleophilic substitution of the chlorine... 

Perfluoroalkyl amines. Thionation of perfluoroacylamines followed by reaction with NBS-BU4NH2F3 constitutes a convenient method for the preparation. 

Similarly, monoalkyl methylphosphonochloridates (eq 8) can be made from dialkyl esters thionate acid chlorides could not be made by this method. Thionyl chloride and PCI5 were also used to make this type of compound (see also Oxalyl Chloride— Dimethylformamide). 

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