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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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(i)
90%
solvents were removed by distillation, and the viscous yellow oily residue was vacuum distilled to give (1) as a white solid (137g, 6%), b.p. 52-54C/0.1 torr, m.p. 27.0-27.5C.
From [5] with permission.
Tris(trimethylsilyl)methanethiol was prepared according to a similar procedure [6].
i) 2.2 n-BuU/l.l TMEDA
ii) 1/8 S8
(Me3Si)3CH ------------------------> (Me3Si)3CSH
lil) HCl
Another one-pot, large-scale procedure for the preparation of thiophenols from unactivated aryl chlorides is available [7]. The reaction of an aryl chloride with a sodium alkanethiolate in NMP as a solvent affords, after acidification, the thiol in a high yield.
ArCl + RSNa ----------> ArSR + NaCl
ArSR + RSNa ----------> + RSR
|H+
ArSH
Example
87%
isolated yield on a 0.6 scale
Such reactions have been previously carried out with more reactive aryl chlorides in HMPA or DMF by Tiecco etal. [8].
In view of their applications in asymmetric synthetic methodology, chiral thiols are currently the subject of much attention. They can be derived from the natural chirality pool as epi-thiomenthol obtained by a Mitsunobu-type reaction [9]. A similar route to (S)-l-phenylethanethiol
(2) has been described [10].
HO H
SCOMe
H SH
The (5)-thioacetate was obtained from the (/?)-alcohol in good yield and with clean inversion of configuration, and smoothly reduced to the (5)-mercaptan (2).
Carefully designed chiral auxiliaries, planned to fulfil specific requirements, find use in synthetic strategy. Such is the case of 1,1'-binaphthalene-2,2'-dithiol (3) prepared in enantiopure form [11,12].
One of the advantages of (3) in asymmetric synthesis is its Q, symmetry. The anion of its dithiepine derivative (4) is used as a chiral version of the formyl anion [11].
Mercaptans are important industrial compounds used in the agrochemical (thiocarbamates, phosphorothioates), pharmaceutical and cosmetic industries as well as in the manufacture of polymers. The main aspects of their industrial syntheses and uses have been reviewed by a specialist in this field [13].
Thiols are often quoted as having particularly disagreeable odours. True enough, like many other sulfur compounds, they often have very low threshold values, and therefore make a large contribution to flavours at concentrations which can be lower than the parts per billion level, for instance 1CH ppb for 1 p-menthene 8-thiol (a constituent of grapefruit juice, see scheme); as pointed by the Firmenich chemists [14] this level corresponds to 1 g in 10 million tons of water! When working with low-molecular-weight sulfur compounds, care must be taken to use appropriate laboratory techniques in order to avoid any leaks or even traces, of compounds with unpleasant, not to say unbearable, smells. The use of bleach to trap volatile products during the reaction, to rinse laboratory glassware and to treat wastes is an excellent and generally sufficient means. On the other hand, organosulfur compounds are widely distributed throughout the living world and they contribute to the odour and flavour of our beverages and foods.
A few example thiols are shown here. Cysteine plays a fundamental role in the chemistry of proteins, mainly due to its easy oxidation to the
SH
(grapefruit)
[14]
[probably the (K)-enantiomer
(coffee aroma) 151
(roast meat aroma) (asparagus)
[16] [17]
cysteine
cystine
disulfide (cystine). The thiol disulfide interconversion is the most remarkable property of the thiol group.
If the alkylation of thiolate anions is the most common method for the synthesis of sulfides [18], some recent routes make use of a reductive thiolation of carbonyl compounds, as in the following one-pot procedure reported by Olah [19]. The scope of the reaction appears to be very large in the choice of the carbonyl compound as well as that of the thiol partner (Table 2.1).
(oxld.l
RSH
RSSR
[red.l
2.2 SULFIDES
O'C. 1 min
]
0 H20:BF3
68-97%
TABLE 2.1
Synthesis of sulfides from aldehydes and ketones
Substrate Thiol Product Yield (%)
PhCHO PhSH Ph^^sPh 91
PhCHO i-PrSH S-I-Pr 97
SPh
1
xr^ PhSH 90
PhSH 8*1 76
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