Lithiated vinyl sulfides

Other lithiated vinyl sulfides bearing a carbonyl group at the / -position have been used in organic synthesis mainly as /3-acyl vinyl anion equivalents858. The 2-(isopropylsulfanylmethylene) derivative 673 has been deprotonated with lithium 2,2,6,6-tetramethylpiperidide (LiTMP) to give the intermediate 674 which, after addition to methyl acrylate and final hydrolysis, afforded the cyclopentenone 675 in 70% overall yield981 (Scheme 175). 

Whereas carbenoid character is definitely present in metalated alkyl vinyl ethers, lithiated alkyl and aryl vinyl sulfides and thioesters, which are easily available by hydrogen-lithium exchange, do not display carbenoid-typical reactions . They rather behave like nucleophilic reagents, so that their discussion is beyond the scope of this overview despite their utility in synthesis The same appiies to various derivatives of enamines, deprotonated in the vinyiic a-nitrogen position - . 

Cycloalkenyllithiums.3 Alkenyllithiums are usually prepared by reductive lithiation of trisylhydrazones of ketones with butyllithium, but this method fails with the hydrazones of cyclic ketones. However, the cycloalkenyl sulfides, prepared by reaction of cyclic ketones with thiophenol, can be reductively lithiated with LDBB at -78°. This lithiation fails in the case of cyclopentenyl sulfides, but is useful in the case of the vinyl sulfides obtained from 6-, 7-, and 8-membered cycloalkanones. 

Intermediates 663 can be prepared by tin-lithium transmetallation with w-BuLi from a-stannylated vinyl sulfides974. Starting from l,l-bis(arylsulfanyl)ethenes, a reductive metallation with lithium naphthalenide at —70°C is a very efficient approach to lithiated vinyl sulfides975,976. Other methods involved bromine-lithium exchange977 or addition of methyl or phenyllithium to thioketenes978. A convenient method for the preparation of l-(methylsulfanyl) and l-(phenylsulfanyl) vinyllithiums was the treatment of 2-methoxyethyl sulfides with 2 equiv of w-BuLi-TMEDA at — 30 °C979. 

Acetone (0.12 mol, 7.0 g) is added to the suspension of lithiated methyl vinyl sulfide, cooled at —70 °C to —90 °C. Five min after this addition the reaction mixture (solution) is treated with 200 ml of water. The aqueous layer is extracted three times with Et20. The unwashed organic solutions are dried over MgS04 and subsequently concentrated in vacuo. Distillation of the remaining liquid through a 20-em Yigreux column gives the carbinol, b.p. 70 °C/12 mm, n 0 1.5012, in 84% yield. 

In 1989 McDougal and co-workers presented an access to some racemic models of the 1 l-oxabicyclo-[6.2.1]undecane framework found in furanoheliangolides (the C/D ring system) [30]. The key reaction of their approach involved the ozonolysis of a functionalized oxa-bridged octalin 27, which provided the desired 1 l-oxabicyclo[6.2.1]undecane framework 28 (Scheme 3). Their synthetic approach started from the Diels-Alder reaction of 2-methyl-3-phenylthiofuran 23 with maleic anhydride. Namely, siteselective a-lithiation of vinyl sulfide 22, prepared from the conjugate addition product of thiophenol and acrolein, then quenching the... 

Preparative Methods by lithiation of phenyl vinyl sulfide with lithium diisopropylamide, followed by silylation, or the base-induced elimination of 2-chloro-l-trimethylsilyl-l-phenylthioethane, or the lithiation of ethyl phenyl sulfoxide with LDA followed by silylation, or the Pd-catalyzed coupling reactions of trimethylstannyl phenyl sulfide with 1-bromo-1-trimethylsily lethylene. ... 

Reaction of l,3-bis(methylthio)-2-methoxypropane with 2 moles of lithium diisopropylamide5 (or w-butyllithium) effects (a) the elimination of methanol to form l,3-bis(methylthio)propene and (b) the lithiation of this propene to generate l,3-bis(methylthio)allyllithium in solution. Its conjugate acid, l,3-bis(methylthio)propene, can be regenerated by protonation with methanol, and has also been prepared (a) in 31% yield by reaction of methylthioacetaldehyde with the lithio derivative of diethyl methylthiomethylphosphonate,5 (b) in low yield by acid-catalyzed pyrolysis of l,l-bis(methylthio)-3-methoxypropane,6 and (c) in low yield by acid-catalyzed coupling of vinyl chloride with chloromethyl methyl sulfide.7... 

The procedure for oxidation of the sulfide to the sulfone is based on that reported earlier by Bordwell and Pitt. The synthetic utility of phenyl vinyl sulfone and sulfoxide derives not only from their ability to serve as excellent Michael acceptors toward such reagents as enolate anions and organometallics, but also as moderately reactive dienophiles in Diels-Alder reactions. " The resulting adducts, in turn, can be chemically modified so that these electron-deficient olefins serve as useful synthons for acetylene,ethylene,terminal olefins,vinylsilanes, and ketene in [4 + 2] cycloadditions. Phenyl vinyl sulfone undergoes ready cycloaddition to Danishefsky s diene in the first step of a protocol for the regiospecific y-alkylation of 2-cyclohexenones. Furthermore, the ready lithiation of phenyl... 

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