Thionating reagents

The microwave-assisted thionation of amides has been studied by Ley and coworkers using a polymer-supported thionating reagent [115]. This polymer-supported amino thiophosphate serves as a convenient substitute for its homogeneous analogue in the microwave-induced rapid conversion of amides to thioamides. Under microwave conditions, the reaction is complete within 15 min, as opposed to 30 h by conventional reflux in toluene (Scheme 7.95). The reaction has been studied for a range of secondary and tertiary amides and GC-MS monitoring showed that it proceeded almost quantitatively. More importantly, this work was the first incidence of the use of the ionic liquid l-ethyl-3-methylimidazolium hexafluorophosphate... 

The use of thiocarbonyl compounds and also trimethylsilyldiazomethane in the Pechmann-Nold synthesis has greatly increased the scope of this reaction in recent years. Wolff s synthesis has also benefited from advances in the synthesis of both diazoketones and thionating reagents. 

Conversion of nitrile using thionating reagent gives the corresponding primary thioamides (Scheme 8). 

Thioureas are most commonly prepared from reaction of isothiocyanates with amines. Also there are some reports on reactions of anime or carbodiimides with several thionating reagents. AA -Disubstituted thioureas bearing double NH groups have been developed as sensors, and as catalysts because of their hydrogen bonding ability. A,A -Disubstituted thiourea-linked sugar chains have been prepared by the reaction of isothiocyanate with amine. 

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. 

Similar to Lawesson s and Daw s reagents. Used as a mild thionation reagent for esters and lactones. 

Another reagent with limited application in thionation reactions has been S2CI2, which afforded intermediates leading to 1,3,4-oxadithiolanes300. However, among the different thionating reagents developed in recent years the most successful has been bis(trimethylsilyl) sulfide, which in the presence of a catalyst affords thioaldehydes... 

Thiopyrans are prepared similarly by the intramolecular cyclization of 1,5-dicarbonyl compounds in the presence of a thionating reagent (e.g., Scheme 117) . 

In the presence of 2,3-dimethyl-2-butene (195), the reaction of (193) with CS2 (194) provides tetramethylethylene sulfide (196) as a product (Equation (28)) <85JOC3228>. This reaction needs a large excess of alkene, because thionation reagents (197) or (198) rapidly decompose with a low energy of activation (Scheme 71). 

Scheme 2.3-10 Polystyrene-supported thionating reagents for the conversion of amides to thioamides.

The thionation from the Lawesson s reagent has been improved by using P4S10 and hexamethyldisiloxane as the thionation reagent, from which the by-products can be easily removed by extraction and column chromatography after the thionation. ... 

This reagent is commercially available and is presently used for many thionations of carbonyl-containing compounds. This is very versatile and efficient, thionating reagent for aromatic, aliphatic, unsaturated, and heterocyclic carboxamides. Lawesson s reagent can thionate carboxamides in the presence of many functional groups. Treatment of 3-A -acylamino ketones with 1 yielded 4//-l,3-thiazine derivatives 2 and 3-A -thioacylamino ketones 3, respectively. By changing the concentration of 1, selective product has been obtained. The 4/f-l,3-thiazines 2 have been produced predominantly when 1 equiv. of 1 was used, while with 0.5 equiv. of 1 the thioamides 3 have been mainly produced (Scheme 2). ... 

A new thionation reagent, (EtAlS) , is the first product of the reaction of triethylaluminium with hydrogen sulphide it reacts with various dimethylamides to form the corresponding thioamides. ... 

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