Methyl dithiocarbonates

S-methyl dithiocarbonate (76S413). Stereoselective isomerization of 1,2-disubstituted alkenes may be achieved by a sequence such as the following fr<2n5-alkene bromo-hydrin -> /3-hydroxythiocyanate -> cw-thiirane -> cw-alkene (75TL2709). 

Dinitrophenyl)ethyl, 187 2-Cyano-1-phenylethyl, 188 S-Benzyl Thiocarbonate, 188 4-Ethoxy-1-naphthyl, 188 Methyl Dithiocarbonate, 189... 

Quebrachitol was converted into iL-c/j/roinositol (105). Exhaustive O-isopropylidenation of 105 with 2,2-dimethoxypropane, selective removal of the 3,4-0-protective group, and preferential 3-0-benzylation gave compound 106. Oxidation of 106 with dimethyl sulfoxide-oxalyl chloride provided the inosose 107. Wittig reaction of 107 with methyl(triphenyl)phos-phonium bromide and butyllithium, and subsequent hydroboration and oxidation furnished compound 108. A series of reactions, namely, protection of the primary hydroxyl group, 0-debenzylation, formation of A-methyl dithiocarbonate, deoxygenation with tributyltin hydride, and removal of the protective groups, converted 108 into 7. 

Symmetrical 5,5-dialkyl dithiocarbonates have been obtained by thermal rearrangement of the corresponding (9,5-dialkyl esters in the presence of Aliquat [43]. This procedure is not suitable for the preparation of unsymmetrical 5,5-dialkyl dithiocarbonates, as it has been reported that disproportionation of the products can lead to a mixture of the symmetrical and unsymmetrical esters. Alternatively, they can be prepared by a base-catalysed disproportionation of 5-alkyl-O-methyl dithiocarbonates [44] (Table 4.9). These methods for the synthesis of the 5,5-dialkyl esters are more convenient than the traditional procedures from the thiol and phosgene. 

Synthesis of symmetrical S,S-dialkyl dithiocarbonates from potassium O-methyl dithiocarbonate... 

The S-alkyl-O-methyl dithiocarbonate, prepared by procedure 4.1.14 from MeOCS2K (48.26 g, 0.33 mol), is extracted from the reaction mixture with Et20 (3 x 25 ml). The ethereal extracts are washed with H20 (3 x 100 ml) and evaporated under reduced pressure at 40°C. Aqueous Na2C03 (2%, 300 ml) is added and the aqueous mixture is stirred at 50°C for ca. 3 h. The mixture is then extracted with EtjO (3 x 50 ml) and the dried (Na2S04) extracts are evaporated under reduced pressure at 70 °C. The temperature of the residue is maintained at 70°C for 30 min and the 5,5-dialkyl ester, which is contaminated with the 0,5-dialkyl ester, the dialkyl sulphide and the disulphide, is isolated by chromatography from silica. 

J. Marco-Contelles, P. Ruiz-Femandez, and B. Sanchez, New annulated furanoses A new free-radical isomerization of an S-methyl hex-5-enylxanthate to an 5-(cyclopentylmethyl) S-methyl dithiocarbonate, J. Org. Chem. 58 2894 (1993). 

The alcohol (10 mmol) and methyl iodide (11 mmol) were added to a two-phase system of CS2 (10 ml) and 50% aqueous NaOH (from 5 g NaOH in 5 ml H20) containing n-Bu4NHS04 (lmmol) in a 50 ml round-bottomed flask. The mixture was stirred vigorously at room temperature by a magnetic stirrer. The reaction was monitored by checking the H NMR spectrum of the CS2 layer. To work up the reaction, the CS2 layer was separated and the aqueous layer extracted three times with CS2 (3 X10 ml). The combined CS2 layers were dried (Na2S04) and filtered. Evaporation of the solvent under reduced pressure afforded pure 0-alkyl 5-methyl dithiocarbonate (Table 2.5). Further purification could be carried out by column chromatography on silica gel or recrystallization for solid samples. 

Allylimidates underwent a clean Claisen-type rearrangement in the presence of 5 mol % palladium chloride (equation 28),40 as did allyl carbamates39 and S-allylthioimidates (equation 29).41 This S to N rearrangement has found application particularly in the synthesis of pyrimidines, systems for which thermal S to N allylic rearrangements were generally ineffective (equation 30).42 Finally, 0-allyI S-methyl dithiocarbonates cleanly underwent palladium(ll)-catalyzed O to S allylic transposition (equation 31 ).43... 

To a mixture of O-Cyclododecyl S-methyl dithiocarbonate (1.0 mmol), Bu3SnH (320 mg, 1.1 mmol) in benzene (5 ml) was added Et3B (1.1 ml, 1.1 mmol, 1 M hexane solution). The mixture was stirred for 20 min, then the solvent was removed and the residue was chromatographed on silica gel to give cyclododecane in 93% yield [40]. 

Tellurium BisfO-methyl dithiocarbonate]1 2.0 g (7.4 mmol) of tellurium tetrachloride and 3.25 g (22.2 mmol) of potassium 0-methyl dithiocarbonate are each dissolved in 40 ml of ethanol. The two solutions are cooled, mixed in the dark, and the cool mixture is filtered. The filtrate is kept at — 20° for a few days, the deposited crystals are collected, washed with petroleum ether, and dried under reduced pressure yield 0.75 g (40%) m.p. 86° (dec.). 

Methylthiosulfonato 4-methoxyphenyl tellurium reacted with sodium thiosulfate, potassium 0-methyl dithiocarbonate, or benzenethiosulfonate with replacement of the methanethiosulfonate group3. 

Unfortunately, introduction of the N-Dts group requires two steps, the first being reaction of the amino group with 0-ethyl S-carboxy methyl dithiocarbon-ate or 0,0-diethyl trithiodicarbonate [Scheme 8.20].32 The intermediate ethoxy-thiocarbonyl derivative is then treated with chlorocarbonylsulfenyl chloride, whereupon chloroethane is extruded to give the JV-Dts derivative. Since the first step is often accompanied by some noisome minor products, a solid-phase variant has been developed for the synthesis of N-Dts-protected amino acids.33... 

The imexpected formation of the methoxy ether (69b) in the reaction of lanosterol 5-methyl dithiocarbonate (69a) with BuaSnH has been reported. Studies using BuaSnD indicated that a hydrogen within the methoxy group originated from the organostannane reagent. A possible mechanism (Scheme 28) was postulated to explain these observations. ... 

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