Thiiranes removal

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

To a mixture of ethyl 5a-cholestan-3-one 2a-xanthate (2 g, 3.95 mmol) and 100 ml methanol is added sufficient ether to completely dissolve the solids. Sodium borohydride (90 mg, 2.36 mmol) is added directly to the reaction flask and the solution is stirred at room temperature for 4 hr. (The use of an excess of sodium borohydride and an extended reaction time produces 5oc-cholestan-2a,3a-thiirane.) The reaction is diluted with 200 ml ether and washed several times with ca. 100 ml water, dried (MgS04) and the solvent is removed under vacuum. The crude sticky gum is chromatographed on a column of 85 g silicic acid. The hexane eluates contain 5a-cholest-2-ene. Ethyl 5a-cholestan-3a-ol 2a-xanthate is obtained in ca. 30% yield by subsequent elution with benzene hexane (1 7) and the desired ethyl 5a-cholestan-3 -ol 2a-xanthate is eluted with ether hexane (1 3) in ca. 30% yield. 

Thiiranes can be formed directly and stereospecifically from 1,2-disubstituted alkenes by addition of trimethylsilylsulfenyl bromide, formed at -78 C from reaction of bromine with bis(trimethylsilyl) sulfide (Scheme 7).12 A two-step synthesis of thiiranes can be achieved by addition of succinimide-A/-sulfe-nyl chloride or phthalimide-A -sulfenyl chloride to alkenes followed by lithium aluminum hydride cleavage of the adducts (Scheme 8).13 Thiaheterocycles can also be formed by intramolecular electrophilic addition of sulfenyl chlorides to alkenes, e.g. as seen in Schemes 914 and 10.13 Related examples involving sulfur dichloride are shown in Schemes 1116 and 12.17 In the former case addition of sulfur dichloride to 1,5-cyclooctadiene affords a bicyclic dichloro sulfide via regio- and stereo-specific intramolecular addition of an intermediate sulfenyl chloride. Removal of chlorine by lithium aluminum hydride reduction affords 9-thiabicyclo[3.3.1]nonane, which can be further transformed into bicyclo[3.3.0]oct-1,5-ene.16... 

The use of optically active enamines in [2 + 2] cycloadditions with thiocarbonyl 5.5-dioxides gives asymmetric induction in the product thiirane 1,1-dioxides. Thus, when thioformaldehyde S,S-dioxide, generated from methanesulfonyl chloride and triethylamine, is treated with optically active AM-phenylethyl-Af-methylpropanal enamine, a mixture of diastereomeric thietane 1.1-dioxides 6 is formed quantitatively. Removal of the chiral 1-phenylethyl auxiliary followed by Hoffmann elimination gives (-+ )-(5)-2-methyl-2//-thiete 1,1-dioxide (7) with 6% ee1,8. 

Two moles of thiirane reacted with 3-aminopropyltrimethoxysilane to afford the expected product of substitution with ring opening (Equation 30) <2001POL929>. The product was then immobilized by reaction with silica gel. Removal of divalent cations (Cu, Co, Ni) from aqueous solution was demonstrated and thermodynamic parameters were determined. 

Fused-ring thiirane A-oxides have been enantioselectively deprotonated by chiral lithium amides 78 or 79. The desymmetrized products were obtained after oxidation of the sulfoxide to remove the additional stereogenic center in good yield and up to 88% ee (Schemes 41 and 42) <1997SL919, 2000J(P1)153>. 

Thioamides of two cyclopropanecarboxylic acids undergo coupling reactions with diazomethane derivatives in refluxing benzene containing rhodium(II) acetate. The reaction conceivably takes place via a thiirane intermediate which undergoes reductive elimination by reaction with excess diazo compound. An example of an intramolecular reaction is the formation of indolizine 2. If the diazo compound is not in excess a thiol is formed, this can be removed by Raney nickel desulfurization. ... 

Aromatic organosulfur compounds such as thiophenes, benzothiophenes and dibenzothiophenes are frequently contained in fossil oil and their sulfur atoms are generally difficult to remove in HDS process [106], In the industrial HDS process, Mo/Co/S or Ni/Mo/S heterogeneous catalysts supported on alumina are widely employed. In order to obtain ideas to develop more efficient catalysts as well as to shed some light on their mechanisms at a molecular level, transition metal complex-mediated cleavages of C-S bond are extensively studied. On the other hand, thiiranes and thietanes are frequently employed for preparation of transition metal sulfides, in which their C-S bonds are smoothly cleaved. In this section, the C-S bond cleavages of thiophene derivatives, thiiranes, thietanes, vinylic sulfides, allylic sulfides, thiols and dithioacetals are overviewed. 

Recently, two methodologies have been published that use very unique approaches to synthesize 4,5,6,7-tetrahydrothieno[3,2-c]pyridine, a key thiophene-containing intermediate en route to clopidogrel. One such approach is the copper-catalyzed ring expansion of vinyl thiiranes followed by oxidation and subsequent removal of the amine protecting group. ... 

Thioketones S=CR2 (R = Ph, C6H40Me-p) react with the benzylidene complex W(CO)5(=CHPh) to form the thiirane derivatives W SC(Ph)HCR2)(CO)5. The thiirane is removed by reaction of these compounds with NEt4Br/CH2Cl2. Results of a mechanistic study on cyclopropane formation from the iron alkyls CpFe (CH3)3X (CO)2 shed light on the selective formation of cis cyclopropanes in the reactions of alkenes with W(=CHPh)(CO)5.227... 

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