Dimerization thioketones

The dimeric thioketone complex 13 was obtained from [PdCl4]2- and thiopivaloylferrocene [Eq. (5)].137... 

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. 

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). 

Polymerization and oligomerization reactions. l-FIalogenopropane-2-thiones give homopolycondensation,10 in different conditions l-chloropropane-2-thi-one11 forms a polymer or a cyclic trimer. a-Oxothioketones12 15 form dimers, by [4+2] unsymmetrical Diels Alder cycloaddition (Scheme 7). a,p-Unsatu-rated thioketones,16 Scheme 3 E = S, form dimers via head-to-head (R1 = Ph, R2 = Me) and head-to-tail (R1 = R2 = Ph), while selenoketones, E = Se, dimerize17 via head-to-head . 

Many cycloaddition reactions have been carried out with ketenes and thioketones. The products are thiolactones (52). Hexafluorothioacetone and diphenylketene, however, do not undergo cycloaddition even after prolonged heating at 100°C. Good results can be obtained when the more stable dimer of this fluorinated thioketone (53) is used. Anionic monomer 54 could be released by the action of potassium fluoride in an aprotic solvent. Two-step cycloaddition to diphenylketene yields ketone 55. 

Dithietanes, dimers of thioketones, are best stabilized by electron withdrawing groups on the ring. They are oxidized to bis-sulfoxide derivatives quite readily, and in at least one case the intermediate dioxide was isolated (Scheme 29) (80AG(E)203). 

One particular class of a,/3 -unsaturated keto-substituted 1,3-dithietanes called desaurins has been known since 1888 (1888CB337). While several specific routes to their synthesis will be outlined later, the one illustrated here (Scheme 110) presumes the intermediacy of an a,/3 -unsaturated keto-substituted thioketone which then dimerizes. The methods used to... 

The reactivity of the complexes 25 is similar to that of a dimeric-orthometallated thioketone complex obtained by the reaction of 2,5-... 

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... 

Indeed, metal carbonyls were also reported to react with thioketones to yield dimeric oletins [319,409]. 

In addition to pyrolysis or photolysis, S,C cleavage may be induced by nucleophiles (or bases) in substrates with an electrophilic (or acidic) center and a leaving group next to the sulfur1. This is exemplified in the treatment of a bridged thiocyanate with potassium terf-butoxide leading to an a-oxo thioketone which spontaneously dimerizes (equation 58)324. 

Pentafluorophenyl thioketones are available [115] from the reaction of the corresponding fluoroketones with B2S3 formed in situ. Oxidation with monoperphthalic acid generated the sulfine, the X-ray structure of which revealed a dimer in the crystal lattice. 

The use of Lewis acids in order to catalyze hetero Diels-Alder reactions of thia-1,3-butadienes is not widespread, but recent investigations stemming from Saito et al. reveal a remarkable acceleration of these transformations in the presence of A1C13 or EtAlCl2 [428]. In a first study concerning asymmetric hetero Diels-Alder reactions of thia-1,3-butadienes, Saito et al. found Lewis acids to have a beneficial effect on the induced diastereoselectivities. Thus, the thioketone 5-17, generated in situ by thermal cycloreversion from its dimer, underwent a completely endo-selective cycloaddition upon treatment with (-)-dimenthyl... 

Dimerizations of dithiiranes/thioketone 5-sulfides to tetrathianes were proposed in some cases (85AGE855,85CB4553 88CL1517). 

Compounds with the thioketone structure frequently dimerize with elimination of sulfur (Eq. II). In the thiopyrone series this was first... 

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