Thio ketones

Carbonyl compounds, such as aldehydes [103, 179], (thio)ketones [31, 94, 180-183], carboxylic acids, and esters [183, 184] with 1 are reduced to alcohols after hydrolysis [5], except in stericaUy hindered cases (see Section 8.5) [185, 186]. Under the same experimental conditions the regioselective reduction of the oxirane ring with 1 gives also the corresponding alcohol [183, 187]. 

Thione-S-oxides react regiospecifically with allyl and benzylsilanes in the presence of a stoichiometric amount of tetra-n-butylammonium fluoride to produce allyl and benzyl sulphoxides [8], cf. the analogous fluoride initiated reaction of thio-ketones and dithiocarboxylic esters with silanes [9, 10]. The yields of sulphoxides... 

Tetrathiametallolanes (343) <94PS(95-96)2i> are useful precursors of analogues of thio-ketones (343) which act as dipolarophiles in (3 + 2)-cycloaddition reactions to give, for example, (400) with mesitonitrile oxide. 

With slight modification, the methods used to prepare fluorothioacyl fluorides can also be used for synthesis of fluorothioketones. Hexafluorothioacetone, the member of this class that has been studied most extensively, is readily obtained by high-temperature reaction of hexafluoropropylene and sulfur (53). The thio-ketone is a deep-blue liquid, bp 8° C, that dimerizes on standing to 2,2,4,4-tetrakis-(trifluoromethyl)-l,3-dithietane. 

Compounds 352, having the same oxidation state of the a,a -carbon atoms in the pyran ring as in compound 349, are obtained on heating thio ketone 350 with 7V-phenylmaleinimide. It was assumed that this reaction proceeds via formation of the intermediate 351, which has the nonclassical tetravalent oxygen heteroatom (69JA3953). 

Keywords carbonyl compound, Lawesson s reagent, microwave irradiation, thio-ketone, tliiolactone, thioamide, thionoester, thioflavonoid... 

The 1,3-dipolar cycloaddition of phosphonodithioformate. S -methanides (41) with aromatic thio ketones (42) yields 1,3-dithiolanes (43) and (44). These S-methanides are also trapped by TCNE, maleic anhydride, A-phenylmaleimide, and dimethyl diazenedicarboxylate (Scheme ll).39... 

The ylide reacts with aldehydes in THF to form epoxides (2) or in THF/HMPA to form phenylthioenol ethers (3).1 The former products rearrange readily to o-phenyl-thio ketones, the latter to homologated aldehydes. 

The behavior of /3-monooxo derivatives of 4-chlomanones (27) toward morpholine was rather complex (98JOC9840). Thus, the proposed thio-ketone S-sulfide 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. S -disulhdes 34. The oxadithiins 31 correspond to a Diels-Alder dimer of 33, and the 1,2,4-trithiolanes 32 correspond to cycloadducts of 33 and 34. 

Dehydrative cyclization of 3-(5-carboxy)-5-phenyl-4-(pyrrol-l-yI)l,2,4-triazole (508) with poly phosphoric acid gave (82G345) the 1,2,4-triazolo[3,4-/7]l,3,4-thiadiazine (509). Ring transformation of 1,3,4-oxadiazoles to 7//-l,2,4-triazolo[3,4-/>]l,3,4-thiadiazines (507) was reported by Sasaki et al. (82JOC2757) through the reaction of [(1,3,4-oxadiazol-2-yl)thio]ketones (123) with hydrazine hydrate in the presence of acetic acid. 

Aldehydes and ketones can be generated from a-chloro sulfides with CuCl2-CuO in high yields [25], The copper promoters can be used both as reagents and as Lewis-acid activators in this reaction to generate the chloro sulfide in situ from a-thio ketones, and 29 is converted directly to 30 in 80 % yield (Sch. 8). The 2-phenylthio-tetrahydropyran 31 could be hydrolyzed to the 2-hydroxy derivative 32, and the bis-phenylthio derivative leads directly to the lactone [26],... 

Thiols efficiently dehalogenate a-halo and a,a-dihalo ketones. Reduction is typically carried out in ethanol containing a weak base. Although this system will also reduce a-thio ketones, it is believed that the halo ketone is reduced, and that reaction proceeds as in equation (11), with a proton from the solvent serving as Lewis acid to assist dehalogenation by thiol (or thiolate). The reactions are of course accelerated by inclusion of a metal salt in the medium. ... 

The secondary alcohol analogs of these ketones are even weaker and the thio ketones are also weak (48). 

Acyclic alkenic sulfur c( npounds have also been obtained via pyrolytic rDA reactions. A general route to thioacrylamides utilizing rDA reactions under FVP conditions has been developed. The rDA reaction of the appropriate adducts yields thioacrylamide, N-methylthioacrylamide and lV,A/-dimethyl-thioacrylamide in approximately quantitative yield (equation 13). The high reactivity of these a,P-unsaturated thioamides had previously limited their availability. a,p-Unsaturated acyclic thio-ketones such as (17) were prepared via a rDA reaction using a FVP technique. These highly reactive species dimerize to 4//-l,3-dithiins (18) on warming to-60 °C (equation M). ... 

Coates et al. have extended this reaction to a method for gem-dialkylation at a methylene group adjacent to a carbonyl group. a-Phenyl thioketones can be alkylated at the carbon bearing sulfur, and the phenylthio group can be replaced by a second alkyl group by reduction-alkylation. For example, the ot-phenyl thio-ketone (1) is treated with sodium or potassium hydride in THF and then allowed... 

One example has been given of a potentially useful version of the benzil-benzilic acid rearrangement in which a-acetoxy-ketones (41), obtained by Pummerer rearrangement of the corresponding a-thio-ketone, undergoes ring contraction to give the a-hydroxy-acid (42), a... 

The thiol ester failed to provide the corresponding a-thio ketone when treated with diazomethane. No insertion was observed when ethyl diazoacetate (Et0C(0)CHN2) or trimethylsilyldiazomethane (Me3SiCHN2) were used with the selenol esters. 

Middleton, W.J. Howard, E.G. Sharkey, W.H. Fluorothiocarbonyl compounds. I. Preparation of thio ketones, thioacyl halides, and thio esters. J. Org. Chem. 1965, 30, 1375-1384. 

This reaction was first reported by Hantzsch and Weber in 1887. It is the formation of thiazole derivatives by means of condensation of a-haloketones (or aldehydes) and thioamides. Therefore, it is generally known as the Hantzsch thiazole synthesis. In addition, other names, including the Hantzsch synthesis, Hantzsch reaction, and Hantzsch thiazole reaction are also used from time to time. Besides thioamides, other thio-ketone derivatives such as thiourea, dithiocarbamates, and ketone thiosemicarbazone can also condense with a-halo ketones (or aldehydes) to form thiazoles. This reaction occurs because of the strong nucleophilicity of the sulfur atom in thioamides or thioureas, and normally gives excellent yields for simple thiazoles but low yields for some substituted thiazoles, as of dehalogenation. This reaction has been proven to be a multistep reaction, and the intermediates have been isolated at low temperatures, in which the dehydration of cyclic intermediates seems to be the slow step. It is found that a variety of reaction conditions might result in the racemized thiazoles that contain an enolizable proton at their chiral center, and it is the intermediate not the final product that is involved in the racemization. Therefore, some modifications have been made to reduce or even eliminate the epimeriza-tion upon thiazole formation. In addition, this reaction has been modified using a-tosyloxy ketones to replace a-haloketones. ... 

In certain cases low-pressure pyrolysis of trithians (654) gives good yields of thio-ketones, e.g. bicyclo[2,2,l]heptane-2-thione (85%) containing >90% of the thione tautomer, which can be kept at room temperature for several days. The initial percentage of enethiol (1 %) only rises to 7% after five days with concomitant partial trimeri-... 

Recent studies > on the reactions with diazomethane of those thio-ketones that cannot exist in the enethiol form yielded conclusive evidence for the occurrence of a 1,3-cycloaddition reaction, because the nitrogen-containing cycloadducts (76) and/or (77) could be isolated under appropriate reaction conditions. Diebert formulated the unstable compound... 

Ethyl thioacetoacetate, or more probably its predominating enethiol tautomer, reacted with p-benzoquinone in the presence of zinc chloride to give the 1,4-adduct (84). The action of methyl iodide on enamino-thio-ketones of the type (21 R = Ar) resulted exclusively in 5 -methyIation. The reduction of adamantanethione to the corresponding thiol by sodium borohydride has been described, and the usefulness of thioketones as scavengers of carbon radicals was demonstrated recently. ... 

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