Thioketones

A number of unsaturated thioketones, bearing only aliphatic substituents, could be isolated [61, 62]. When the products possess protons on the a carbons, they were accompanied by the tautomeric enethiols [62]. When this form was favored, some authors carried out the [3,3] shift in acetic anhydride as a solvent and isolated the corresponding thiolester [63, 64]. Recently, the rearrangement of tung-sten(pentacarbonyl) complexes of sulfides was reported to lead to the corresponding thiocarbonyl derivatives [65]. 

Synthesis.—The highly hindered thioketones (14)—(17) have been prepared [in the yields shown] by the reaction of triphenylphosphorylidene hydrazone with elemental sulphur, by heating the mixture at 130—140 C under vacuum (1—5 mmHg). The yields are considerably improved when the corresponding hydrazones are allowed to react with disulphur dichloride in the presence of triethylamine in benzene, at 0 °C to room temperature. With the latter.method, the yields of (15)—(17) are quantitative. Thioketones (18)—(20) have also been 

A modification of the Pinner reaction provides a facile device to prepare )ff-thioxo-esters from the corresponding yS-enamino-esters in DMF, the thiones 

When the thione (17) is photo-excited to its 7r,7r -state, hydrogen-abstraction from alkanes and cycloaddition to olefins takes place, which is in remarkable contrast with the reactivity of (17) in the n, r -state.  

When xanthenethione (38) is excited to its ,7r -state, [2 + 2]cycloaddition proceeds with bis(alkylthio)ethyne. The cyclo-adduct [(42) or (43)] is in thermal equilibrium with its open isomer [(44) or (45)]. A similar reaction of (37) with acenaphthylene, indene, or A-phenylmaleimide affords a spirothietan derivative in good yield. Thioxanthenethione in the ,7r -state cyclo-adds to alkyl- or alkoxy-substituted butatrienes, giving the thietans (46)—(49).  

Tamagaki, R. Akatsuka, M. Nakamura, and S. Kozuka, Tetrahedron Lett., 1979, 3665. 

Synthesis.—Simple aliphatic and alicyclic thioketones are prepared easily and in high yields by the same method as described in the preceding section for the preparation of the enethiol tautomers of simple aliphatic 

On the other hand, the action of hydrogen sulphide on 2-acetylcyclo-pentanone and l-acetylindan-2-one, respectively, gave products that were tentatively formulated by the authors as (27) and (28), respectively. However, the reaction is known to be quite susceptible to temperature effects, and the possibility cannot be excluded that the formation and isolation of the latter products instead of the immediately expected mono-thio-)8-diketones, which according to experience with similar compounds should possess reasonable stabilities, is merely a consequence of the relatively high reaction temperature (- 10 °C). The use of the reaction of vinylic chlorides with hydrogen sulphide, or its anion, as a suitable route to thioketones has been further demonstrated by the syntheses of (29) and (30).  

New examples of thioacylation of active-methylene compounds with thiono- or dithio-esters have been reported. Some new l,3-dithiol-2-ylidene-thioketones have been prepared by the cycloaddition reaction between acetylenes and l,2-dithiole-3-thiones. The latter compounds and their imino-analogues yielded related cycloadducts (31) on treatment with ketens. The reaction of l,2-dithiole-3-thiones with a-chloro-benzylidenephenylhydrazine in basic medium gave the thioketones (32) by 

The well-known synthesis of enamino-thioketones (21) using the reaction of 1,2-dithiolium salts with primary or secondary amines has been the subject of renewed investigation. Duguay and Quiniou observed that the action of p-methylaniline on unsymmetrical 3,5-diaryI-l,2-dithiolium 

Maguet, Y. Poirier, and J. Teste, Bull. Soc. chim. France, 1970, 1503. 

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The mechanism of the Hantzsch s synthesis was studied at a very early stage by several authors. The intermediates were generally assumed to be open-chain a-thioketones, but in a series of papers by Murav eva and Schukina (470, 490) the isolation of hydroxythiazolines from the reaction between a-haloketones and a variety of thioureas was reported. 

It is interesting to note that in each of these cases only one intermediate, either the a-thioketone (93) or the hydroxythiazoline (94), was isolated from the reaction mixture, thus suggesting that hydroxythiazolines are in equilibrium with the corresponding a-thioketones. Similar conclusions are implicit in Baganz and Roger s production of 4-formylthiazoles by this synthesis (625). 

The prefix thioxo- is used for naming =S in a thioketone. Sulfur analogs of acetals are named as alkylthio- or arylthio-. For example, CH3CH(SCH3)OCH3 is l-methoxy-l-(methylthio)ethane. Prefix forms for -carbothioic acids are hydroxy(thiocarbonyl)- when referring to the O-substituted acid and mercapto(carbonyl)- for the S-substituted acid. 

Another indole/oxindole synthesis achieves the critical ortho-substitution by Sommelet-Hauser rearrangement of an anilinosiilfonium ion intermediate. Use of P-thioketones (G = R, an alkyl group) generates 2-substituted indoles, whereas P-thioesters (G = OR) lead to oxindoles. In each case, a 3-thio substituent must be removed by desulfuri2ation. 

Two further compounds are on the borderline of stability. The oxathiirane (14), obtained by photorearrangement of a thioketone 5-oxide, could be characterized by its UV spectrum (76JCS(P1)1404). Thiazirine (15) was stable only at 15 K (78JCS(P1)746). 

We proposed new photometric reagent 4,4 -bis(diethylamino)-thiobenzophenone (ethyl derivative of Michler s thioketone, EMT) for the determination of free chlorine and chloramines in drinking water. 

Thioketones and aldehydes readily polymerize to the trimer and isolation of the monomer is difficult. 

The cyclic thioketone, 3-oxotctrahydrothiophene (11), gives a mixture of enamines (12,13) when caused to react with a secondary amine such as piperidine or pyrrolidine (31). The enamine mixture can be reduced to the 3-aminotetrahydrothiophene using formic acid or oxidized to the 3-amino-thiophene using diisopentylsulfide. 

Hydrogen chloride has also been eliminated from sulfinyl chlorides by addition of triethylamine. The thioketone oxide obtained from 9-fluorene-sullinyl chloride reacted with morpholinocyclohexene to give a zwitterionic adduct (475). 

A -Methylation of the NH of heterocycles using 1 is also known as exemplified by the methylation of indole/ The interesting mechanism is delineated below. O-methylation of weak acids such as phenols, carboxylic acids and oximes as well as 5-methylation such as A -phenylisorhodanine, certain thioketones, and dithiocarboxylic acids have also been reported." ... 

Tile behavior of /3-moiiooxo derivatives of 4-chlomaiioiies (27) toward morpholine was rather complex (98JOC9840). Tlius, the proposed thio-ketoiie 5-sulhde intermediates 28 would dimerize into either 1,2,4,5-tetrathianes 29 in a two-step manner or to 1,3,4,5,6-oxatetrathiocins 30 by a [5 + 3] cycloaddition. Meanwhile, the formation of oxadithiins 31 and 1,2,4-trithiolanes 32 is suggestive of the disproportionation of 28 into the thioke-tones 33 and the thioketone 5 -disulhdes 34. Tlie oxadithiins 31 correspond to a Diels-Alder dimer of 33, and the 1,2,4-trithiolanes 32 correspond to cycloadducts of 33 and 34. 

Tliiobenzophenone 5-sulfide (35) was successfully generated by a cycloreversion of the 1,2,4-trithiolane 36 at 60°C or by a sulfur transfer from thiiranes to tliiobenzophenone (87JA902 97T939).Tlie thioketone 5-sulfide... 

A ring opening of the dithiirane 39 to the thioketone 5-sulfide 35 was proposed for the reaction of thiobenzophenone 5-oxide (40) with the thioketone 41 (81LA187). Tlie conjugation with the phenyl group would stabilize 35 relative to the dithiirane form. 

Tlie isolable dithiiranes (4 and 7) are fairly stable under acidic conditions but quickly lose a sulfur atom to give the corresponding thioketones under basic conditions (97BCJ509). Tliey are quite sensitive toward amines and phosphines. Oxidation with MCPBA gave the corresponding dithiirane 1-oxides in high yields. 

Tlie thermal reaction of dithiiranes is of particular interest in relation with the dithiirane/thioketone 5-sulfide manifold. Heating 5-oxodithiiranes (4) in solution led to both isomerization to 6,7-dithia-8-oxabicyclo[3.2.1]-octanes 74 and desulfurization to 5-oxothiones 75, the ratio of which was dependent on the reaction conditions employed. The intramolecular [3 + 2] cycloaddition of the thioketone 5-sulfide 76, generated by ring-opening, provides a straightforward explanation for the formation of 74. Meanwhile, 75 is probably formed by a nucleophilic attack on the sulfur atom by another molecule of 4 and/or by elemental sulfur formed during the reaction. 

Tlie thioketone 5-oxide 85, generated from allene 86 and SOCk in situ, decomposes to give the alkene 87. A mechanism, involving the transient formation of the 1,2-dithietane 88 (by dimerization of 85 followed by rearrangement), was proposed (85AGE855). 

All unexpected reaction is the formation of dithiete 175, thiirene 1-oxide 185, and thioketone 186 by the treatment of di-l-adamantylacetylene with S2CI2 (99UPl).Tlie yield of each compound is 30% at most. 

In a manner similar to carbonyl compounds, thioketones react with lithiated (2,S )-2,5-dihvdro-2-isopropyl-3,6-dimethoxypyrazines to give the 2,5-trun.s-adducts 2 with the diastereomeric excess exceeding 95% 12. The adducts can be further modified to give vinylglycine derivatives12. 

Kobayashi and Mutai75 have recently reported an interesting rearrangement of the 1,4-dithiin sulfone (53) to the thiophenes (54) and (55) (equation 12). While 54 presumably arises as a result of simple photoextrusion, the rearranged thiophene (55) is postulated to arise via the valence isomer (56), followed by cyclization to the thiophene, concomitant with, or preceded by, loss of S02. Some support for the intermediacy of the thioketone (56) was revealed by the isolation of the pyrrole (57), when the photolysis was conducted in n-butylamine. Compound 57 presumably arises by cyclization of the iV-butylimine analog of 56 initially formed. 

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