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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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1,2 manner (the usual way for less stabilized more reactive thiocarbanions). The chemistry of these thioacetal monoxides was developed in the 1970s mainly by Ogura and Tsuchihashi [287-290] and by Schlessinger and coworkers [291-293]. Two examples of application are given.
A synthesis of m-jasmone [293] illustrates the Michael addition to methyl vinyl ketone of a stabilized carbanion and the hydrolytic step with a protonic acid.
j CHO
ii) NalO
II) H2, Lindlar
In the synthesis of a-amino acids [290] through addition of the carbanion of MMTS to nitriles the overall process involves three other steps frequently encountered in sulfur-mediated chemistry: a Pummerer-type rearrangement, with a less common migration of a methylthio group, and a Raney nickel desulfurization following transesterification of the thioester function.
SMC I) HNa/THF
Me H3o
R SMe SMe
II

)
(2)
(3)
Raney nickel
AcNH
R|COaMe H
(4)
(5)
Synthesis of an amino ester (5, R = Ph)
Benzonitrile (1.520g, 14.8mmol) was added to the THF solution of the sodium salt generated from (1) (1.830g, 14.8 mmol) by the action of sodium hydride (1.24 eq) at room temperature, and the resulting solution was stirred at 50C for 16h. After addition of water (2 ml) together with dichloromethane (70 ml), the mixture was dried over anhydrous sodium sulfate (without separation of the aqueous layer) and the solid phase was filtered off. Evaporation of the filtrate under reduced pressure and subsequent crystallization from dichloromethane/carbon tetrachloride/ cyclohexane (1:1:1) afforded (2) as a crystalline material (2.391 g, 10.5 mmol), m.p. 162-163C (105 mg of (2) could be recovered by chromatography on silica gel of the mother liquor residue of evaporation; the total yield of (2) was 75%).
A mixture of (2) (2.439 g, 10.7 mmol), acetic anhydride (1.5 ml, 15.9 mmol), and pyridine (1.0ml, 12.4mmol) in dichloromethane (10ml) was stirred for 4h at room temperature. After evaporation of dichloromethane, the residue was washed with water to give the thioester (3) (2.593 g, 9.64 mmol), m.p. 174-175.5C.
A solution of (3) (215 mg, 0.799 mmol) in methanol (10 ml) was refluxed for 13 h in the presence of two drops of triethylamine. After column chromatographic separation (silica gel, dichloromethane), crude methyl ester (4) (192 mg, 0.759 mmol) was obtained, m.p. 166-167C (recrystallization from dichloromethane/carbon tetrachloride/n-hexane and water/methanol). Crude (4) thus obtained was treated with
deactivated Raney nickel (1.2 g) in acetone at room temperature for 5.5 h to afford the methyl ester of N-acetyl phenyl glycine (5) (144 mg, 0.696 mmol). The deactivated Raney nickel was obtained by refluxing Raney nickel of W-II activity in acetone for several minutes prior to use.
From [294] with permission.
N-Acetylphenylglycine was obtained directly in a 91% yield when a solution of (3) in methanol/water (9:1) was refluxed for 3h in the presence of potassium carbonate (2 eq). A desulfurization by the methylthiolate anion produced by the hydrolysis of (3) accounts for this result [295]. In that way N-acetyl phenylglycine was obtained in a 60% yield, by a three-step procedure, from benzonitrile.
The method described above was applied to synthesize the methyl ester of ui.-/V-acetyl-5 hydroxy tryptophan [294].
Ogura [296, 297] has proposed other interesting uses of MMTS (also known as FAMSO, for formaldehyde dimethyl dithioacetal 5-oxide) and also of the two following dithioacetal monosulfones:
methyl methylthiomethyl sulfone, MeSCH2S02Me;
methylthiomethyl p-tolyl sulfone, MeSCH2S02Tol (commercially available).
With these reagents [296] alkylation could be obtained under phase transfer conditions. Cleavage of the alkylated product to yield a carbonyl compound was performed under neutral conditions by photolysis in the presence of water.
AcNH
4SMe hv (254 nm)
----------
S02Tol H2
R
SMe
4
R-CHO
Acid-sensitive functional groups could thus be preserved as an acetal in the example below:
Page et al. (see [298] and references therein) have shown that generally excellent stereocontrol in organic reactions can be obtained by using DITOX (1,3-dithiane-l-oxide) derivatives as chiral auxiliaries. The one-pot stereo-controlled cycloalkanone synthesis given here outlines some aspects of the chemistry worked out for efficient acylation-alkylations steps. Of note are: the use of N-acyl imidazoles under mixed base (sodium hexamethyldisilazide/n-butyllithium) conditions to yield the lithium enolates of 2-acyl-l,3-dithiane-l-oxides) and the sequential alkylation-cyclization of the latter (steps (iv) and (v)).
i) NHMDS (1.1 eo), THF, -78C, 15 min.
ii) n-BuIi (1.1 eq) 78C, 15 min.
ffi) RCHjCO-Imid (1.1 eq), -78C to rt, 2 h
iv) (1.0 eq) -78 to rt, 16 h
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