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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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Me(CH2)5CHO i-PrSH Me(CH2)5CH,S-i-Pr 86
A good yield was obtained only if the boron trifluoride monohydrate was added, at ice bath temperature, to the CH2C12 solution of the other components: heptanal, i-PrSH and Et,SiH.
Thiolation of aldehydes and ketones: general procedure
In a typical reaction, the aldehyde or ketone (lOmmol) and thiol (11 mmol) were dissolved in dichloromethane (10ml). The mixture was cooled to 0C using an ice bath. H20:BF3 (1ml) was added to the mixture, which was stirred at ice bath temperature for 1 min. Et3SiH (15 mmol) was added and the solution was stirred for 3h, during which time it warmed up to room temperature. The mixture was poured into ice water (30ml) and extracted with dichloromethane (3 x50 ml). The organic layer was separated and washed with water (2x25 ml), 10% sodium hydrogencarbonate (3x25 ml) and water again (2 X 25ml), and finally dried (MgSO). The solvent was removed on a rotary evaporator, and the sulfide thus obtained was purified by distillation or recrystallization.
From [19] with permission.
Sulfides can be prepared from alcohols. A convenient conversion under mild conditions and in high yields has been published [20]. The work-up is particularly simple.
Efficient procedures for the direct preparation of allyl sulfides from allylic alcohols have also been reported pi].
i) BF3.-Et20/CH2C12 R2SH or R2SSiMe3 rt, 5-48 h
II) NaHC03/H20
The radical addition of thiols to alkenes, another general route to sulfides, was found [22] to be initiated by 9-BBN, leading to a remarkably efficient and simple method for the preparation of dialkyl sulfides.
. , 9-BBN. cat . ,
R-CH=CHo + r2sh --------------------> r-ch2ch2- sr2
THF. 0C to rt
Sulfides by addition of thiols to alkenes
To THF (10 ml), the alkene (5 mmol), 9-BBN (0.025 mmol, 0.5% equiv) in THF, and an alkanethiol (5 mmol) were added successively at 0C and the mixture was stirred for Ih at the same temperature. The dialkyl sulfides were isolated directly by simple distillation (without any work-up procedures). Yields: 78-99%.
From [22] with permission.
The chemistry of crown thioethers and thioether cages is a fast-developing field [23], and their synthesis involves a caesium carbonate ring closure [24,25].
9 S3 18 S 6 a thioeiher cage [26]
or or
i9) ane S3 (18)aneS6
A new type of approach to thiocrown ether synthesis involving a [2 + 2] coupling of -dithiol and a>-dihalide units in the presence of a boron aluminium alkoxide couple has been described [27].
For example:


THF, MeOH/NaOMe (01)/1(01)


(1) (2) (3)
To a solution of B(0-i-Pr)3 (5 mmol) in THF (250ml) was added A1(0-
i-Pr)3 (lmmol) and MeOH (40 ml). The mixture was refluxed for 30 min, after which Na (20 mmol) was added. The mixture was then refluxed until the sodium had dissolved. (1) (10 mmol) was introduced over 15 min. The solution was subsequently refluxed again for 60 min. The mixture was kept under reflux and a solution of (2) (lOmmol) in THF (75 ml) was added dropwise over a period of 8-10 h. After the addition was complete, stirring was continued for 4h. The mixture was evaporated to dryness and the residue was redissolved in CH2C12. The organic layer was washed with brine to remove the boron and aluminium salts. The solvent was removed in vacuo and the residual solid was chromatographed over silica gel with CH2Cl2/hexane 2:1 as the eluent. The organic layer was evaporated to provide the product (3) in a 52% yield.
From [27] with permission.
If most of the research on crown and cage thioethers has concerned their synthesis and exploratory work on their coordination chemistry, their complexing properties and capacity to stabilize low oxidation states of transition metals should be expected to lead to new applications, as for their oxygen and nitrogen analogues.
We have noted previously (see Section 2.1) the role played in biochemistry by the thiol disulfide interconversion, and the disulfide unit is a fundamental feature of the structure of peptides and proteins. The sulfur-sulfur bond between two cysteins link remote parts of a peptide chain or cross-link two such chains. Cleavage of these bonds in the hair protein keratin, followed by reoxidation, gives hair its desired shape.
A number of naturally occurring compounds with a disulfide unit have shown interesting biological activity [28, 29]. Nereistoxin, charatoxin, asparagusic acid, a plant growth inhibitor, and lipoic acid, a key co-factor in the oxidative decarboxylation of pyruvate, are examples taken in the
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