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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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R'WSR> r2 SR4 R2 ,R2
R\ R\ /
) + CSo >- /=\ .
Ra/ R SR4
- : :x
x - -SiR3. -P(0)(0R)2. -P R3
(respectively Peterson, Homer and Wlttig oleflnaUons)
Olefination of carbonyl compounds and the reaction of esters with activated thiols such as Al(SPh)3 [65] or Me2AIS(CH2)n SAlMe2 [66] (n = 2,3) are valuable routes.
Ai|SPh}3 R\_____/SPh
xylene, reflux r2' '<
R1R2CHC02Me
Me2AlS(CH2)3SAlMe2 R1. ,S V rt R2''s_7
It should be noted that at room temperature a thioester is obtained [65] from the reaction of an ester with Al(SPh)3 (or Me2AlSPh). S-t-Bu thioesters used as activated carbonyls were similarly prepared [67].
? CH2C12 i?
PhCH2COMe + MegAlSPh ---------------> PhCH2CSPh
Bis(dimethyluluminiurn) 1,3-prupuritdUhialult 0C
MeaAl + HS-(CH2)3-SH -------> MejAlS- (CH2)3-SAlMe2
(3)
A solution of trimethylaluminium (61.2 ml, 1.63 in toluene) was diluted with degassed methylene chloride (110 ml), cooled to 0C, and treated dropwise with dry 1.3-propanedithiol (5.04 ml). After addition was completed (40 min), the cooling bath was removed and the mixture stirred at 25C for 1 h to give the reagent (3).
From [66] with permission.
2- (3-Cyclohexenylidene) -1,3-dithiane
CHO
To a toluene/methylene chloride solution (88 ml) of the reagent (3) prepared as described above was added a solution of methyl 3-cyclohexenecarboxylate (3.5 g) in methylene chloride (50 ml) in one portion. After 2 days at room temperature, the reaction mixture was concentrated by rotary evaporation, the residue was diluted with ether, and moist sodium sulfate (a few grams) was added. Filtration through dry sodium sulfate and concentration of the ethereal filtrate yielded the partially crystalline ketenethioacetal, which was further purified by chromatography on silica gel with 1:1 benzene/hexane as the eluent to provide pure (4) (3.58 g, 72%), m.p. 42-43C.
From [66] with permission.
Metallation of (4) followed by protonation gave (5), and (6) was obtained by hydrolysis of the dithiane.
A one-pot synthesis of the conjugated ketenedithioacetals (7) and (8) involving indirect lithiation of propene or isobutene via the potassio deriviative reaction with carbon disulfide and 5,5-dime thy lation has been reported [68]. It illustrates some aspects of the reaction of organometallics with CS2.
R = or Me
+ t-BuOLi
SLi (+t-BuOLi)
Mel
(7) R = H
(8) R = Me
l,l-Bis(methylthio)-1,3-butadiene and
3-methyl-l ,1 -bis(methylthio)-1,3-butadient
A solution of n-butyllithium (O.lOmol) in hexane (75ml) was diluted with tetrahydrofuran and cooled to -95C (cooling bath with liquid nitrogen). The solution was stirred and liquid propene (8.42 g 0.2 mol) or isobutene (11.225 g, 0.2 mol) was added, followed by the addition (over 1 min) of a solution of potassium t-butoxide (11.3g, 0.10mnl) in THF (30ml), care being taken that the temperature remained below -80C. The cooling bath was then gradually withdrawn and the temperature of the mixture allowed to gradually rise (over 30 min) to -20C. To the stirred yellow suspension was then added a solution of anhydrous lithium bromide (10.5 g, 0.12 mol, obtained by heating the commercial anhydrous salt at 150C under a vacuum of 10-15 torr for 30 min) in THF (40 ml). The colour faded to a very light yellow. The suspension was again cooled to -110C, and carbon disulfide (7.6 g, 0.10 mol) was added over a 30 s period with vigorous stirring and with intense cooling. The temperature of the dark-red solution might rise to -80C. After 10 min, methyl iodide (42 g, 0.30 mol, excess) was added at 80C, and the temperature of the yellow mixture was allowed to rise (over 20 min) to +10C. Water (100ml) was then added, the organic layer was separated and the aqueous layer was extracted with pentane (3 X 50 ml). The organic phases were combined, washed with ammonium chloride solution (100 ml), dried with magnesium sulfate, and concentrated under a water pump vacuum. The residue was distilled under an oil pump vacuum to give the pure ketene 5,5-acetal (7) or (8): (7), yield 11.7g (80%), b.p. 48-50C/l torr; (8), yield 13.7 g (86%), b.p. 62-641 torr.
From [68] wilh permission.
A one-flask procedure, based on the counter attack strategy , involving Me3Si-SiMe3 as the counter attack reagent was used in the synthesis of ketenedithioacetals from 1,3-dithiane and a carbonyl partner [69]. The scheme given here summarizes the process.
SiMe3
%
2.6 SULFOXIDES
For general references on the preparation of sulfoxides, see [70][74].
Sulfoxides are easily obtained by oxidation of sulfides. They can be further oxidized to sulfones. Many reagents have been used, and the possibility to synthesize selectively sulfoxides and sulfones, often in the presence of other sensitive functionalities, is an important feature for synthetic applications. The reaction is well documented [75], and only a few notable aspects are mentioned here.
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