Thioketones from ketones

Only the mechanism for the formation of thioketone from ketone is illustrated here. 

Thionation of Ketones. The synthesis of thioketones from ketones by use of LR was described decades ago but several new review articles on this fundamental reaction have been published in recent years. ... 

In the second group we consider interconversions of functional groups with the exchange of hetereoatoms, breaking of old and formation of new C-heteroatom bonds. Examples of these transformations are interconversion of an amide to ester, thioketone to ketone or alkylhalide to alcohol. They are related to S5mthetic reactions formation of amide from ester, thioketone from ketone or haloalkane from alcohol. Characteristic of all the above interconversions is the disconnection (imaginative process ) of the C-heteroatom bond, C-N or C-O. In the synthetic direction C-N, C-S and C-Hal bonds are formed. Therefore, such FGIs are also denoted as DIS-C-X, where X stands for heteroatom. 

A3-l,3,4-Thiadiazolines were easily prepared from ketones or thioketones. By pyrolysis in the presence of a phosphine they afforded olefins [128,441] (see Section 4.5.4). 

Other dipolarophiles have been tested leading to pyrrolidines (from vinyl sulfones),219 oxazolidines (from ketones) and thiazolidine (from a thioketone) in moderate to good yields. Noteworthy is the isolation of two adducts from ethoxycrotonaldehyde a pyrrolidine carbaldehyde implying cycloaddition onto the ethylenic double bond and an oxazolidine resulting from the cycloaddition on the carbonyl moiety of the dipolarophile.219 438... 

Thioketones markedly differ from ketones in their reactions with electrophilic reagents.1,4 Ketones react chiefly at the a-carbon atom, whereas with thioketones the electrophile preferentially attacks the sulfur atom (thiophilic addition), leading to derivatives of the enethiol. The reactions are often performed in the presence of a base (Scheme 15). Thus, alkylation and acylation yield the enethiol derivatives (24) and (25). Similarly, reactions with an arenesulfenyl chloride, with carbon disulfide followed by an alkyl iodide, and with a carbonyl compound afford the compounds (26), (27) and (28), respectively (Scheme 15). The mechanisms of formation of the last two products are depicted in Scheme 16. 

Synthesis of thiazolines from ketones, sulfur and NH3 with the possibility to obtain thioketones. 

Hexamethyldisilthiane convens ketones to thioketones in the presence of Me3SiOTf, gives diallyl sulphides from the alcohol using 130.BF3, peptide thioacids from the Kaiser s oxime ester resin, and2H-l,2-dithiole-3-thiones from ketones and CS2 using NCS. Ph3SiSH... 

The addition of H2S to an aldehyde or ketone can result in a variety of products. The most usual product is the trithiane (8). ° ot-Hydroxy thiols (5) can be prepared from polychloro and polyfluoro aldehydes and ketones.Apparently, compounds 5 are stable only when prepared from these compounds, and not even for all of them. Thioketones (6) can be prepared from certain ketones, such as diaryl ketones, by treatment with H2S and an acid catalyst, usually HCl. They are often unstable and tend to trimerize (to 8) or to react with air. Thioaldehydes are even less stable and simple ones apparently have never been isolated, though t-BuCHS has been... 

The first examples of intramolecular diene transmissive HDA reactions have been reported. Thus, the divinyl thioketones, derived from the ketones by treatment with Lawesson s reagent, spontaneously cyclise to the thiopyran derivative (27) and react further as shown <96CC811>. 

Treatment of hydrazones derived from 1-adamantyl phenyl ketone, pivalophe-none and benzophenone with sulfur monochloride gave pentathianes 232 and hexathianes 233 along with the corresponding ketones and thioketones as the main products (1997H255 Scheme 124). 

BC13 convert 0=0 groups of ketones, lactones, and lactams to G=S groups119 and H2S-Me3SiCl-i-Pr2NLi converts carboxylic esters to thiono esters.120 Carboxylic acids RCOOH can be converted directly to dithiocarboxylic esters RCSSR, 120a in moderate yield, with P4S, and a primary alcohol R OH.121 Thioketones can also be prepared by treatment of ketones with P4SI0,122 and from oximes or various types of hydrazone (overall conversion C=N------> C=S).123... 

Another route to thioaldehyde and thioketone complexes uses the tungstate [W(CO)5SH] as the precursor. When [W(CO)5SH] was treated with ketones in the presence of trifluoroacetic acid, thioketone complexes [W(CO)5 S = C(R1)R2 ] were formed. Analogously, thiobenzaldehyde complexes were obtained from [W(CO)sSH]- and benzaldehydes bearing electron-releasing para substituents. Benzaldehyde, benzaldehydes with electron-withdrawing substituents, and aliphatic aldehydes did not react. Presumably, the binuclear dianion [p,-S W(CO)5 2]2 is an intermediate in the reaction, as on acidification of a mixture of [ju,-S W(CO)5 2]2 and p-N, A -dimethylaminobenzaldehyde the thioaldehyde complex [W(CO)5 S = C(C6H4NMe2-p)H ] is formed.143... 

The reactions of dinuclear thioaldehyde and -ketone complexes with PR3 take a different course. When the dimeric complexes 112 are treated with PMe3 a Ti-S bond in 112 is cleaved and the monomeric complexes 113 are reversibly formed (see Scheme 26), 69 The reaction of 112 with benzene-thiol led to a Ti-C cleavage and formation of 1,3-propanedithiolato-(phenylthiolato) complex.69 The reaction of binuclear p-191 rf-thioketone molybdenum complexes related to 115 (M = Mo, E = S, R = Aryl) with P(OEt)3 also gave mononuclear complexes [Mo(CO)2(Et) i72-S = C(Aryl)2 (i75-C5H5)] by a rather complicated reaction sequence. When other phosphites were employed additionally binuclear complexes derived from addition of the phosphite to one molybdenum atom were isolated.225... 

In a related approach, a, /i-unsaturated thioketones, formed in situ by thionation with P4S10 of the corresponding ketones, undergo intramolecular hetero-Diels-Alder reactions263. Diethyl thioxomalonate was formed from diethyl oxomalonate and phosphorus pentasulfide (equation 29) and was trapped as a Diels-Alder adduct264. 

The typical Wittig-type intermediates, that is, 1,3,2-oxathiaphosphetane derivatives, were isolated from the thionation reaction of .r-bicyclo[3.3.0 octane-3,7-dioncs with Lawesson s reagent <1998EJ02647>. However, under similar conditions both ketones and the corresponding thioketones formed a mixture of trans- and as-1,3,2-dithiaphosphetanes 26a and 26b and 66a and 66b (Scheme 34), <2004TL1331>. 

The replacement of a tert-butyl group by SiMe3 going from di-ferf-butyl ketone to rerr-butanoyl trimethylsilane and from di-terf-butyl thioketone to ferf-thiobutanoyl trimethylsilane lg increased Xmax and deshielded the quaternary carbon. Furthermore, an inversion in polarization of the C=S bond and a decrease of the HOMO-LUMO energy differences were observed in the ferf-thiobutanoyl trimethylsilane with respect to di-rm-butyl thioketone. 

A reaction which is applicable to the synthesis of imidazoles substituted at C-4 by sulfur substituents is the interaction of a-chloro-a-phenyl thioketones (prepared from the corresponding diazoketones) with ammonia and carboxylic acids. Although the detailed reaction course is yet uncertain, it bears a close resemblance to the reactions of a-chloro ketones with amides. The method has been used to prepare 2-ethyl-4-methyl-5-phenylthioimidazole (145) using ammonia, propanoic acid and 1-chloro-l-phenylthiopropanone (Scheme 82). 

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