Books
in black and white
Main menu
Home About us Share a book
Books
Biology Business Chemistry Computers Culture Economics Fiction Games Guide History Management Mathematical Medicine Mental Fitnes Physics Psychology Scince Sport Technics
Ads

Sulfur reagents in organic - Metzner P.

Metzner P., Thuiller A. Sulfur reagents in organic - Academic press, 1994. - 200 p.
Download (direct link): sulfarreagents1994.djvu
Previous << 1 .. 8 9 10 11 12 13 < 14 > 15 16 17 18 19 20 .. 67 >> Next

From [117] with permission.
Interestingly, exclusive ipso substitution was observed in the reaction of trialkylarylstannanes with arenesulfonyl chlorides [118]. Diaryl sulfones, with substitution patterns different from those available via electrophilic aromatic substitution, were obtained in good to excellent yields. The
example shows how an acetal group could survive the reaction run under non-acidic conditions.
54% Isolated yield
2.8 THIOCARBONYL COMPOUNDS
Undoubtedly the taming of many reactions involving thiocarbonyl functions in the preparation as well as in the uses of such compounds for organic synthesis has been one of the greatest successes of organosulfur chemistry in the last two decades. General and reliable methods have been developed for their syntheses, and recent reviews on the preparation of thioaldehydes (1), thioketones (2), thionoesters (3), dithioesters (4) and thioamides (5) are available and quoted in [119, 120]. A few general features are given hereafter.
s g s s s
r,Ah riAr2 rI^OR2 r'^SR2 R^NR?
(1) (2) (3) (4) (5)
2.8.1 Thioaldehydes
Except when R1 is a very bulky substituent (see [121] and references therein for stable thioaldehydes) they are usually not stable at ambient temperature or in solution. They are prepared and used in situ as in the
2.8 THIOCARBONYL COMPOUNDS example given here [122].
Silicon-assisted synthesis of thioaldehydes and trapping
A solution of the aldehyde (1 mmol), the diene (1.5 mmol) and bis(trimethylsilyl) sulfide (2 mmol) in acetonitrile (0.5 ml) was treated at room temperature with a solution of CoCl2.6H20 (0.2 mmol) in acetonitrile (2.5 ml). Progress of the reaction was monitored by GC/MS analysis. The reaction mixture was quenched with saturated ammonium chloride, extracted with ether and dried over sodium sulfate, and the solvent removed under vacuum. The crude reaction product was then purified by column chromatography or TLC on silica gel. For R1 = Ph a 94% yield was secured.
From [122] with permission.
The reaction proved to be highly chemoselective, allowing thionation of aldehydes in the presence of other carbonyl groups. As a noticeable exception acylsilanes were converted to thioacylsilanes [123].
The use of CF3S03SiMe3 as a catalyst allowed the thionation of ketones as well as aldehydes. Stereochemical control of the Diels-Alder adducts could be achieved by varying the molar ratio of the sulfurating agent.
A similar direct conversion of aldehydes to thioaldehydes has been achieved [124] using Me3SiSSiMe3 and a catalytic amount of n-BuLi.
Photolysis of phenacyl sulfides [125] and the base-mediated 1,2 elimination reaction of sulfenyl derivatives [126] are other general methods of preparation of these reactive species.
Ph ^O
hr]
Et-iN n
ZCHjjSX -i-----> A
-XH Z H
-
s
z
2.8.2 Thioketones
The catalysed reaction of hydrogen sulfide on ketones or their acetals, or the thionation of carbonyl derivatives by tetraphosphorus decasulfide, or some modified version of this phosphorous compound as Lawesson, Davy and Heimgartner reagents are classically used [119, 120] to prepare the thioketones (2).
R\ 1 orii R\
>=o------------- V=s
R R2
(2)
i) H2S/HC1 or H2S/HCI.
11) P4S10
f/S Lawesson : R = 4-Me-Ph
\ /jj ^ Davy: R = alkylthJo
S S Heimgartner : R = 4-MeS-Ph
However, for aliphatic low-molecular-weight members of this class, oligomerization and/or polymerization, formation of gera-dithiols and enethiolization are often observed. The purification steps can be tedious and the obtention of pure products difficult. There is still a need for progress in this field. Although much less used, another general method whose scope appears important [127] involves the reaction of ketimine
anions with dialkylthioformamide or, better, with carbon disulfide to generate a cyclic four-membered ring intermediate which subsequently decomposes to the thione (2).
i
V-N R\
^Ijiou 2)=s +UNCS
R2
This method has been applied to the synthesis of di-t-butyl thioketone [128].
1) Na \ ,H
Cl -------------> >=N
Di-t-butyl ketone imine
Pivalonitrile (33.2 g) and t-butyl chloride (44.4 g) were added under nitrogen over 1 h to a well-stirred suspension of sodium sand (18.4 g) in a mixture of light petroleum (80 ml), THF (20 ml) and methanol (1ml), keeping the reaction temperature between 15 and 20C during addition. The mixture was stirred for 3h. Chlorobenzene (2 g) in THF (5 ml) was added dropwise over 10 min, and stirring continued (1 h). Methanol (20 ml) was cautiously added over 0.5 h, followed by water, until clear phases separated. The aqueous phase was extracted with ether (3 x50 ml). The combined organic phases were dried and concentrated under reduced pressure. Distillation afforded the pure imine (63%), b.p. 62-63C/19 torr.
Previous << 1 .. 8 9 10 11 12 13 < 14 > 15 16 17 18 19 20 .. 67 >> Next