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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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CH2=C-S-C=C=CH2 PMS.H*> n-Bu -C=C-CH2-CH2CO-Me . I U CaCOi. 130C
(E)-trisubstituted olefins were obtained stereoselectively [491] via dithioesters (Y = SMe).
4.5.1 The thio-Claisen rearrangement
Y = H. R. SR
The dithioester was converted into an ester by CuCl2/CuO in ethanol.
Allylic thionesters, dithiocarbamates and thionocarbamates are starting materials for various synthetic purposes [203, 492,493]. General synthetic routes, from Nakai et al. [492], to a,0-unsaturated esters and ketones via the [3,3] sigmatropic rearrangement of allylic thionocarbamates (1) are featured in the accompanying schemes.
V . Yi
R2^ ft R'T'O'^NMe,
it) Me2N-C-Cl R
F? H, Me
M = MgX. Li
Me2N-C(-S)-Cl is commercially available or easily prepared
E = C02R (3)
(2) COR4 (4)
CH2R5 (5)
The thiolcarbamates (2) are the common precursors for the esters (3) or ketones (4).
(2) MeSSMe " R^=YSCONMe2
R1 R3
ROH. HgCl2 \___________/
ii) E l ?2
) H20/Hg0:BF3 o
The thermal rearrangement of an allyl xanthate to a dithiocarbonate was used to introduce the sulfur atom on a quaternary carbon in the synthesis of agelasidine A, a natural S-containing sesquiterpene [494].

Agelasidine A
Some applications of the thio-Claisen rearrangement to the syntheses of thiocarbonyl compounds, particularly unsaturated dithioesters and thionesters, and of its stereocontrol aspects are reviewed in [120]. A particularly high stereoselectivity was observed with 5-allyl derivatives of P-hydroxydithioesters: syn products were obtained exclusively, according to the accompanying scheme [495,496].
I) LDA (2 eq] THF. -78C SMe n>Br/\^R
ill) h2o
syn-Methyl 2-(l-hydroxyethyl)-pent-4-enedithioate by the thio-Claisen rearrangement
Methyl 3-hydroxybutanedithioate (R = Me) (0.6 g; 4 mmol) was added dropwise to a solution of LDA (2 eq) in THF cooled at 78C. The mixture was stirred for 20 min. The yellow dithioester colour disappeared. Allyl bromide (1 eq) was added. Stirring was maintained for 45 min. The solution was quenched by an aqueous solution of ammonium chloride. The mixture was partitioned between ether and brine. The organic layer was washed with brine, dried with magnesium sulfate and concentrated. The crude ketene dithioacetal was left at ambient temperature for X d to achieve the rearrangement. A yellow oil was isolated by flash chromatography (elution with a 90:10 mixture of cyclohexane/ethyl acetate), yield: 74%, as a 90:10 syn/anti mixture of diastereoisomers.
From [495] with permission.
The reaction was extended to the stereoselective synthesis of compounds bearing three chiral carbons with syn,syn arrangement [497, 498].
Cyclic stereocontrol using this transposition was investigated in the thionolactone series [499].
Applied to dialkenyl disulfides, the dihetero sigmatropic shift gives rise to 1,4-dithiocarbonyl derivatives. The precursors are easily obtained by oxidation of the enethiolates, and the reaction has been observed with thioketones [500]. thioamides [501], dithioesters [356, 502] and thionesters
syn syn syn, syn
syn syn
A number of [3,3] sigmatropic rearrangements involving sulfur, related to the organosulfur chemistry of onion and garlic, were investigated and reviewed by Block [186]. The sulfoxide thio-Claisen rearrangement yielding sulfines and the rearrangements of mono- and disulfoxides derived from dialkenyl disulfides are noteworthy.
1,2-Asymmetric induction has been reported for a ketene Claisen rearrangement of the adducts of dichloroketene to chiral ally] thioethers as a route to precursors of optically active -y-butyrolactones [504]. An example of this sigmatropic step is given hereafter.
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