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

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 .. 37 38 39 40 41 42 < 43 > 44 45 46 47 48 49 .. 67 >> Next

This method has been reviewed by Kocienski [420J, together with his own fluoride-induced elimination of 0-trimethylsilyl sulfones.
R4 W Na[Hg)
R3 i) Ac20
R2^ R4
The reductive elimination of (3-hydroxyimidazoyl sulfones by samarium iodide was claimed to be an improved variation of the Julia olefin synthesis [421].
Alkenes by reductive elimination of (3-hydroxyimidazolyl sulfones
To a stirred solution of samarium diiodide (1.5 mmol) in THF (12 ml) was rapidly added a solution of a p-hydroxy sulfone (0.5 mmol) in THF (6 ml) under an argon atmosphere. After 15 min at room temperature the reaction mixture was still blue, due to an excess of Sml2. The reaction mixture was then poured into a 10% solution of Na2S203 (20ml) and extracted with ethyl acetate. The residue was chromatographcd over silica gel (hexane/ethyl acetate 99:1) to give the alkene (55-82%) as a mixture of (?)/(Z) isomers.
From [421] with permission.
Many examples are found in the literature in which the reaction of an a-sulfonylcarbanion with an electrophile is followed by a base-induced elimination of a sulfinic acid.
In most cases conjugation of the double bond in the final product is at the origin of an efficient process [422,423].
fl n-BuLi THF/HMPA
PhS02-(CH2)6-CH3 + BrCH2C02Et
ii) Na2COa/EtOH
co2r OH
i) t-BuOK
A vitamin A synthesis is based on such a method [422], and the process is industrially applied by Rhone Poulenc [424].
Z - C02Me CH(OMe)2 CH2OH
Elimination of sulfinic acid from ketosulfones was also a key step in an expedient synthesis of a,0-unsaturated ketones via the Michael adducts of sulfonyl carbanions to nitroalkenes. Conversion of the resulting nitronates into ketones was most conveniently realized by ozonolysis. DBU-promoted elimination of sulfinic acid completed the process. Overall yields range from 71 to 88% for the examples reported [425].
'2 -78 to -20C
PhSOa R R2
Ley [426] has reported a case of spontaneous elimination of benzenesulfinic acid in the reactions of the anion of 2-benzenesulfonyl-tetrahydropyran with electrophiles. A convenient synthesis of spiroketals followed.
. Q ^ Ol,
SOaPh WE 1
The starting material (1) is commercial. It can be prepared as follows or from 2-methoxytetrahydropyran [426].
3,4-Dihydro-2//-pyran (1.11 g, 13.2 mmol) was added dropwise to a stirred solution of benzenesulfinic acid (1.88 g, 13.2 mmol) in dry dichloromethane at room temperature under argon. Stirring was continued for 2h, then the solvent was removed under reduced pressure and the product recrystallized from diethyl ether/petroleum to give 2-(benzenesulfonyl)tetrahydro-2#-pyran (1) (2.45 g, 82%) as white needles, m.p. 78C.
From [426] with permission.
Condensation of the anion of2-(benzenesulfonyl)tetrahydropyran with electrophiles
The sulfone was dissolved in dry THF at -78C under argon, n-Butyllithium was added dropwise and the mixture was stirred at -78C for 15 min, then the electrophile added and the solution allowed to warm to room temperature over 1.5-2h. It was then poured into a sodium bicarbonate solution and extracted with ether (2x20 ml). The ethereal extracts were dried and evaporated to give the crude adduct, which was purified by column chromatography on Florisil, eluting with light petroleum/diethyl ether mixtures or by kugelrohr distillation.
From [426] with permission.
(3) is a pheromone of the olive fly Dacus olae [426].
A solution of the anion of (1) (2.2 mmol) was treated with 1-(tetrahydro-2#-pyran-2-yl)oxy-4-bromobutane (0.52 g, 2.2 mmol) as above. Work-up and distillation gave (3) (265 mg, 77%) as a colourless oil, b.p. 100C/25 torr.
From [426] with permission.
The synthesis of both enantiomers of matsutake alcohol (a mushroom flavour compound) outlined in the accompanying scheme shows how the sulfinyl group was used to introduce a methylene unit via methylation and regioselective elimination steps [427].
n-Buli (2.3 eq). -78C to rt
Mel (l.leq), -78C
(mixt. of stereoisomers)
reflux overnight
y?)-matsutake alcohol 65% yield, 94% e.e.
The required (R)- and (S)-P-hydroxysulfides were easily obtained from the same (/?)-epichlorhydrin through enantiodivergent synthesis (R = n-Bu in the scheme).
4.3.3 Carbonyl methylidenation with sulfoximines and other derivatives
Many other sulfur-derived reagents have been used in reactions quite similai to those derived from sulfones and mainly for carbonyl methylidenation (see [419] for general references), as in the Johnson sulfoximine method [428].
Previous << 1 .. 37 38 39 40 41 42 < 43 > 44 45 46 47 48 49 .. 67 >> Next