Diketones, reaction with sulfur

Julid investigated the behavior of terfuran 22 and bis(thienyl)furan 23 by cyclic voltammetry as well as the EPR spectra of the radical cations derived from these two compounds. Condensation of the diketone 20 with sulfuric acid furnished furan 22 in 18% yield, while reaction of diketone 21 with hydrochloric acid produced 23 in 84% yield.In a related report, Luo prepared oligomeric bis(thienyl)furans via similar methodology. ... 

Diketones yield exclusively /1-fluorovinyl ketones, e.g. 19, on reaction with sulfur tetra-fluoride at 20 C in diethyl ether.64... 

The halogen atoms of the geminal dihalo derivatives of diaryl diketones and of heterocyclic ketones can be replaced in reactions with sulfur compounds 0e.g., sodium hydrogen sulfide, thioacetic acid, phosphorus pentasulfide), thioketones being formed.318,319 Staudinger and Freudenberger,320 for instance, obtained thiobenzophenone in 46% yield from benzophenone dichloride (dichlorophenylmethane) and a hot alcoholic solution of sodium hydrogen sulfide ... 

Thioketals are readily formed by acid-catalyzed reaction with ethane-dithiol. Selective thioketal formation is achieved at C-3 in the presence of a 6-ketone by carrying out the boron trifluoride catalyzed reaction in diluted medium. Selective protection of the 3-carbonyl group as a thioketal has been effected in high yield with A" -3,17-diketones, A" -3,20-diketones and A" -3,l 1,17-triones in acetic acid at room temperature in the presence of p-toluenesulfonic acid. In the case of thioketals the double bond remains in the 4,5-position. This result is attributed to the greater nucleophilicity of sulfur as compared to oxygen, which promotes closure of intermediate (66) to the protonated cyclic mercaptal (67) rather than elimination to the 3,5-diene [cf. ketal (70) via intermediates (68) and (69)]." " ... 

An interesting bridged-sulfur compound, which is a natural constituent of Iranian oil, has been synthesized 478) by the reaction of a bicyclic bis-enamine with sulfur dichloride and subsequent Wolff-Kishner reduction of an initial sulfur-bridged diketone. Sulfur dichloride has also been added to a number of vinylogous amides 479). 

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

Other examples of this synthetic strategy are known for example, a recent zirconium polymer by Illingsworth and Burke (8), who joined amine side groups of a zirconium bis(quadridentate Schiff-base) with an acid dianhydride to give amide linkages. Once again, caution is necesary, as Jones and Power (2) learned when they attempted to link metal bisO-diketonates) with sulfur halides that is, they obtained insoluble metal sulfides because the p-diketone complexes which they used were fairly labile and the insolubility drove the reactions to completion in the wrong direction. 

These methods are limited in scope. Direct thiation has been reported for the transformation of vicinal diketones to [3,4]-annelated thiophenes <1996CHEC-II(7)49>. Thionations and selenations of vicinal halomethyl ketones with thioacetamide or iV,iV-diethylselenopropionamide as sulfur and selenium donors, respectively, have also been reported <1996CHEC-II(7)49>. In a recent example, thieno[3,4-f]pyrazoles 160 were readily prepared from aryl 5-bromomethyl-l//-l-phenylpyrazole-4-yl ketones 159 by reaction with thioacetamide (Equation 35) <1998JHC71>. Additionally, an example of an amination cyclization by reaction of 161 with benzylamine to afford pyrrolo[3,4-i/ thiazole 162 has been described (Equation 36) <1998JHC71>. 

Aromatic esters may be used to aroylate the dianions derived from 1,3-diketones by reaction with potassium amide (60JOC538). Not only are acetyl and benzoyl acetones suitable for reaction, but alicyclic diketones and 2-hydroxyacetophenone are also acceptable. Cycliz-ation of the triketones occurs in cold sulfuric acid, presumably via the enolic form and the hemiacetal (Scheme 132). 

As a modification of this procedure, one can consider the reaction of ketones with sulfurating agents leading to thioketones which next react via a [2+2] cycloaddition to furnish 1,3-dithietanes. Thus the reaction of 1,5-diketones with Lawesson s reagent afforded fused 1,3-dithietanes 186 in high yields (Equation (31) Table 9) <1997BCJ509, 2000JOC1799>. 

A modified procedure for the preparation of pyrazoles includes the solventless condensation of diketones and hydrazines in the presence of a catalytic amount of sulfuric acid at ambient temperature <2004GC90>. 1,3-Diketones can be synthesized directly from ketones and acid chlorides and then converted in situ into pyrazoles by the addition of hydrazine <2006OL2675>. The possible modifications to the 1,3-dioxo component in the reaction with hydrazines include the use of -ketoesters, -ketonitriles, -halocarbonyl compounds, -hydroxyketones, -sulfonylketones, and 1,3-dihaloalkanes . 

Chloroprene is dimerized to 54 when heated. When the dimer is treated with sulfuric acid, hydrolysis to 1,4-cyclooctanedione occurs and this diketone experiences transannular closure under the reaction conditions.100 ... 

The overall reversibility of the process was shown by the recovery of 2-octanone when 2,2-bis(difluoroamino)octane was shaken with H2S04 at room temperature for 1 hr (17). In the presence of strong acids, aldehydes (RCHO) react to give bis(a-difluoroaminoalkyl)ethers [RCH-(NF2)OCH(NF2)R, 50-60% yield], and gem-bis(difluoroamino)alkanes [RCH(NF2)2, 20-40% yield] (108, 109). The reactions of HNF2 with a-hydroxyketones and a-/ -diketones in fuming sulfuric acid lead to difluoroamino-l,3-dioxa-2-thiolane-2,2-dioxides (215). 

A one-pot synthesis of 4-hydroxycyclopent-2-en-l-ones (150), involving (Z)-stereoselective olefination of a-diketones to give (149) followed by intramolecular aldol condensation, has been reported. Wadsworth-Emmons reactions of bis(2,2,2-trifluoroethyl)phosphono sulfoxides (151) with aromatic aldehydes give predominantly (Z)-a,p-unsaturated sulfoxides while similar reactions with the corresponding sulfides (152) give ( )- or lower (Z)-selectivity. In olefinations using (5)-dimethyl phosphorylmethyl p-tolyl sulfoxide (153) substantial racemisation at sulfur occurs when -butyllithium is used as base. ... 

MacDowell and Patrick127 effected cyclization of 359 to a diketone (24%, m.p. 335°C) and reduction to 360 (22%, m.p. 216°C) (Scheme 29). However, their sample of 360 appears to be different from the product of m.p. 292°C described by Friedmann, and ascribed structure 360, from the reaction of sulfur with indene at 180°C.1,128 MacDowell and Patrick obtained only intractable tar from the Friedmann procedure. A double cyclization was also employed by Cagniant and co-workers (Scheme 30). 29... 

Diketones. This alkylation of ketimines has been extended to the synthesis of 1,4-diketones by use of a 2,3-dihalopropene as the alkylating reagent. The reaction is carried out with the carbanion, prepared as described above and then diluted with IHF at -60°. The resultant vinylic halide is then hydrolyzed with sulfuric acid at -20 to 0°. 

Protection of 1,2-diols. These reagents are prepared from the diketones and HC(OMe)j in methanol containing a little sulfuric acid. By an acid-catalyzed exchange reaction, 2,3-dimethoxy-l,4-dioxane derivatives are formed in the reaction with 1,2-diols. Diequatorial diols are selectively protected. Actually, the protection can be performed directly by the reaction of a 1,2-diol with an a-diketone, trimethyl orthoformate, in methanol in the presence of camphorsulfonic acid. ... 

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