Thioketones thioamides

There are a considerable number of complexes of thioketones, thioamides, thioacids and thiourea, some examples being (68) and (69).532,536... 

Table 4.23 - Sulfur bases thioketone, thioamides, thioureas [73] and isothiocyanates [87]. Table 4.24 - Sulfur bases thiols, thioethers, disulfides [92], aromatic thioethers (sulfur and 7T bases) [96].

The torsional barrier of the amino group in thioamides is generally ca. 2 kcal/ mol higher than in the corresponding amides (26), and this trend is also found in the enamino thioketones (17,23 Table 2). The increased conjugative interaction in the thioamides is reflected in the Ct—C2 barriers, and the larger size of sulfur compared to oxygen affects the EIZ population ratio. 

C, and then three molecular equivalents of acetyl chloride and triethy-lamine were added. Three types of acetylated materials, 11, 12, and 13, were isolated accompanied by a small amount of thioketone 7 and thioamide 9 (Scheme 8 and Table 6). All of the acetylated materials showed optical activity. For the reaction of 6a, 84% ee of 2-(acetylthio)aziridine 11a, 50% ee of 4-(acetyl-thio)oxazoline 12a, and 20% ee of 4-(acetylthio)oxazolidin-2-one 13a were obtained in 39,10, and 16% yields, respectively. In the reaction of 6b,c, the corresponding optically active materials 11-13 were obtained as shown in Table 9. The formation of oxazoline 12 involves the rearrangement ofAT-acyl aziridines, which occurs by intramolecular attack of the carbonyl oxygen at the ring carbon to cause rupture of the system. 

Primary, secondary and tertiary thioamides and thionreas are readily converted to their corresponding 0x0 analogs with Oxone in refinxing CH3CN . Thiono esters were converted to esters, while thioketones remained intact nnder these reaction conditions. Hydrazines can be selectively converted to esters and acids in high yields by nsing Oxone in an alcohol and a water, respectively . However, Mane and coworkers showed that hydrazides can be smoothly converted into the corresponding Af,Af -diacylhydrazines in excellent yields with Oxone in water (equation 67) . ... 

Applied to dialkenyl disulfides, the dihetero sigmatropic shift gives rise to 1,4-dithiocarbonyl derivatives. The precursors are easily obtained by oxidation of the enethiolates, and the reaction has been observed with thioketones [500]. thioamides [501], dithioesters [356, 502] and thionesters [503],... 

Table 4.41. 13C Chemical Shifts of Selected Thio- and Thiono Acids and Esters [73m, 331], Thioamides and Thioureas [332, 333], and Thioketones [334] in Comparison to the Corresponding Carbonyl Compounds (<5C in ppm).

Lawesson s Reagent is a mild and convenient thionating agent for ketones, esters, and amides that allows the preparation of thioketones, thioesters and thioamides in good yields. 

But the more heteroatoms, the more alternatives. We could disconnect the enamine first 27a and the C-S bond second 31. This suggests a reasonable a-halo-ketone 33 and an unstable-looking imine 32. Fortunately this is just a tautomer of the thioamide 34. Though thioketones are unstable, thio-amides are stable thanks to extra conjugation. 

Thiocarbonyl compounds have recently emerged as synthetic tools with specific properties. Although some thioamides and thioketones were prepared as early as the 19th century, general methods are rather recent. Nowadays most, if not all, thiocarbonyl compounds that one can imagine can be prepared, with techniques adapted to the stabilities of the target molecules. 

We present here the most recent reports, arranged by chemical group thioamides, dithioesters, thionoesters, thioketones, thioaldehydes and sul-fines. 

The increasing utilisation of thiocarbonyl compounds brings about the necessity for efficient procedures for their transformation into carbonyl compounds. A straightforward method [172] involves the treatment of a thioketone with 4-nitrobenzaldehyde in the presence of TMSOTf. Thus thio-benzophenones and thiocamphor are converted into the corresponding ketones, but aliphatic thioketones or thioamides are resistant under these conditions. In order to convert an easily accessible bis(thiocamphor), de-... 

The mechanism of the Hantzsch synthesis has been established and is shown in Scheme 165. Substitution of the halogen atom of the a-halo ketone by the sulfur atom of the thioamide occurs first to give an open-chain a-thioketone (232), which under transprotonation proceeds to give a 4-hydroxy-A2-thiazoline (233) in aprotic solvents, or a thiazole (234) by acid-catalyzed dehydration of the intermediate thiazoline in protic solvents. 

The application of the Hantzsch synthesis to monosubstituted thioamides affords the corresponding N-substituted thiazolylium salts. This method is particularly valuable for the preparation of those thiazolylium compounds in which the substituent on the ring nitrogen atom cannot be introduced by direct quaternization, for example the synthesis of aryl or heteryl thiazolylium salts. In that case the intermediate a -thioketone can usually be isolated, its conversion into the thiazolylium salt occurring by simple heating (Scheme 166). 

Simple thioaldehydes and thioketones are too unstable to exist and attempts at their preparation lead to appalling smells (Chapter 1). The problem is the poor overlap between the 2sp2 orbital on carbon and the 3sp2 orbital on sulfur as well as the more or less equal electronegativities of the two elements. Stable thiocarbonyl compounds include dithioesters and thioamides where the extra conjugation of the oxygen or nitrogen atom helps to stabilize the weak C-S bond. 

The size difference between carbon and sulfur atoms leads to relatively inefficient overlap of -tr-orbi-tals in the C=S bond. Consequently, thiocarbonyl compounds are in general highly reactive and have a tendency to di-, oligo- or poly-merize. This is particularly true for thioaldehydes, thioketones, and thio-ketenes. In contrast, thioamides (1) are usually perfectly stable and can be handled without problems. This stability can be understood in terms of a pronounced resonance interaction between the C =S TT-bond and the nonbonding electron pair on nitrogen. The analogous electron delocalization prevails in thiolactams. ... 

Fragmentary reports describe the aminometallation of an ester, thioketone or thioamide and for the most part are unexceptional. 

Phosphorus pentasulfide is a valuable reagent for conversion of carbonyl into thiocarbonyl groups for instance, amides are converted to thioamides, ketones to thioketones (see Chapter 8, p. 137), carboxylic acids to thioacids, and alcohols are converted to the corresponding phosphorodithioic acids (18) (Scheme 16). 

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