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Sulfur reagents in organic - Metzner P.

Metzner P., Thuiller A. Sulfur reagents in organic - Academic press, 1994. - 200 p.
Download (direct link): sulfarreagents1994.djvu
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From [99] with permission.
(R)-(+)-Methyl p-tolyl sulfoxide
A solution of methylmagnesium iodide (prepared from methyl iodide (40.6 g, 0.286 mol), magnesium (5.96,0.245 g atom) and ether (250 ml)) was slowly added to a solution of (-)-menthyl (S)-/>-toluenesulfinate (60g, 0.204mol) in anhydrous benzene (200 ml) between 0 and 10C. After the addition, the mixture was stirred at room temperature for 2h and then hydrolysed with a saturated aqueous solution of ammonium chloride (200 ml). The aqueous solution was extracted with ether (100 ml). The organic layer was finally washed with saturated brine (100 ml) and dried with sodium sulfate. After evaporation of the solvent, the oily residue was mixed with hot hexane until formation of a pale-white cloudy precipitate. Crystallization occurred on cooling to 5C overnight. The white crystals were dissolved in a minimum of hot ether, and -hexane was added to the solution until formation of a pale-white cloudy precipitate, and cooled to -5C. The crystals formed were filtered and the mother liquor concentrated and
submitted to the same treatment, affording white crystals (25 g, 80%), m.p. 73-74C, [aJD21 = +192 (c 1.2 in CHC13), [a]D21 = +146 (c 2.0 in acetone).
From [99] with permission.
The use of a chiral sulfite derived from ethyl (S)-lactate is noteworthy [94, 100, 101], as shown in the scheme. A regioselective cleavage at the more hindered site occurs first when R1 is a bulky group. A second displacement reaction affords the chiral sulfoxide. The regioselectivity of the first step is completely reversed when a small organometallic reagent (EtMgBr for instance) is used in that step (for a discussion of this strategy and references, see [94]).
A new class of chiral sulfinyl transfer reagents, much more reactive towards Grignard reagents than the Andersen menthyl sulfinate ester, have been introduced by Evans [102] and reacted with a wide range of nucleophiles to afford chiral sulfoxides, sulfinate esters or sulfinamides efficiently. These reagents are shown below:
The enantioselective chemical and enzymatic oxidations of sulfides [86, 94] have also received many interesting developments. High e.e. values have been obtained independently by Kagan [103,104] and Modena [105] via modified Sharpless reagents and by Daviss group [106], which used various chiral oxaziridines.
ethyl (S)-lactate

Me Ph
PhCH2
28
SOa
sof o
Cl
Oxidation of thioethers derived from the natural chirality pool, the readily available lactic acid and 3-hydroxybutyric acid, has been used in molar-scale preparation of enantiomerically pure sulfoxides: methyl (S)-2-(phenylsulfinyl)acrylate and (R)-isopropenyl p-tolyl sulfoxide [107].
Specific cases of enzymatic oxidation give excellent results (see [108] for a comprehensive review and [94] for some more recent references).
Oxidation of sulfides and sulfoxides, as discussed above, and alkylation of sulfinate salts are the most common methods used to obtain sulfones for synthetic purposes [71, 109-113]. A hydrogen peroxide-urea-phthalic anhydride system was recently proposed as a mild convenient reagent for the efficient preparation of sulfones from organic sulfides [114].
Sulfonylation of aromatic hydrocarbons in the presence of a Lewis acid and the reaction of sodium benzenesulfinate with alkyl halides proved to be particularly easy and useful to prepare starting materials for the Julia olefination procedure (see Section 4.3.2).
A recent method for the highly chemoselective oxidation of sulfides to sulfones using '-methylmorpholine N-oxide (NMP) and a catalytic perruthenate was found to be also applicable in the presence of isolated or allylic double bonds [115].
Ph.
i ..O S
ToL ..'O
2.7 SULFONES
v
Urea / H8Oj / phthalic anhydride

R1
McCN, 20C
PhSOjjNa + RX ---------> PhS02R
A number of methods for the preparation of vinyl and allyl sulfones are available [109, 110], and the syntheses of vinyl sulfones from alkenes has been reviewed [116]. A simple one-step procedure of wide applicability makes use of a palladium-catalysed cross-coupling reaction between aryl and alkyl sulfonyl chlorides and substituted vinyl and allyl stannanes
[7].
R'S02C1 + n-BugSnR2 l^P)'lPd *- RISOaR2 + n-Bu3SnCl
R1 alkyl, aiyl R2 = vinyl, allyl
The following procedure is representative.
(E )-Slyryl p-lolyl sulfone
To a solution of /Moluenesulfonyl chloride (200mg, 1.0 mmol) in dry THF (5 ml) was added (?)-styryltributylstannane (430 mg, 1.1 mmol) followed by tetrakis(triphenyl phosphine)palladium(O) (12mg, 1.0mol%). The resulting pale-yellow solution was heated at 65-70C for 15 min with stirring. The reaction mixture was cooled to room temperature, diluted with ethyl acetate and treated with an excess of aqueous KF for 2-3h with vigorous stirring. The precipitated tin fluoride complex was removed by filtration and washed with ethyl acetate. The organic layer was separated, washed with brine and dried (Na2S04). The solvent was removed on a rotary evaporator and the residue was purified by flash chromatography to give (?)-styryl p-tolyl sulfone (0.19g, 77%), m.p. 121-122C (hexane/EtOH).
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