Organolithium with sulfur

The reaction is initiated by the attack of the organolithium at sulfur to produce the pentacoordinate sulfur species. This seems to be the prime reaction of all electron-deficient sulfur compounds with organolithiums (Eq. 45). 

Bis(phenylselanyl)methyllithiums 429 (R = H) are stable till 0 °C and were initially trapped with deuterium oxide, methyl iodide and benzophenone639. a-Substituted organolithium intermediate 429 (R = Me, w-CgH ), prepared with LiTMP in THF/HMPA at — 20 °C, reacted with alkyl bromides, ethylene oxide and benzaldehyde to give products 430 in good yields (Scheme 113)640. Bis(methylselanyl)methyllithiums 431 have been allowed to react with different electrophiles to afford products 432 (Scheme 113)640. Alkylated products have been deprotected with mercury(II) chloride or copper(II) chloride/copper(II) oxide, and by oxidation with hydrogen peroxide or benzeneseleninic anhydride644. Deprotection of selenoacetals to ketones can also be performed with sulfuric acid645. 

In a number of derivatization reactions it is advisable to replace the original counter ion by another one. As mentioned in Sects. II-6 and II-9, organolithium compounds give much better results than potassium compounds in reactions with enolizable carbonyl compounds and with sulfur, selenium and tellurium. On the other hand, alkylations with alkyl halides and with oxiranes proceed more smoothly with the potassium intermediates. Although HMPT may be used as a co-solvent, simple replacement of lithium by potassium may give similar results combination of the counter ion and solvent effects may be even better. The replacements Li+ K + and K+ Li+ are generally fast reactions in a wide temperature range (compare e.g. [161,241]) ... 

Unsymmetrically substituted sulfides can be accessed by reactions between sulfenyl derivatives R -S-X [R = alkyl, aryl X = Cl, OCH3, A-imidazolyl] with an organolithium reagent. Organolithiums react with selenium and tellurium compounds e.g., with diphenyl diselenide or with phenyltellurium bromide ) in the same way as with sulfur compounds if sometimes less effectively. 

Sulfur diimides react readily and quantitatively with organolithium reagents at the sulfur centre to produce lithium sulfmimidinates of the type Li[RS(NR )2] x- ° The lithium derivatives may be hydrolyzed by... 

Whereas the reactions of sulfones with nucleophiles via pathways A and B of equation 1 are most frequently observed, the nucleophilic substitution reaction by pathway D has been observed only in the cases where the leaving carbanion can be stabilized, or in the highly strained molecules. Chou and Chang3 has found recently that an organolithium reagent attacks the sulfur atom of the strained four-membered sulfone in 34. When this sulfone is treated with 1 equivalent methyllithium, followed by workup with water or Mel, 38 or 39 are formed in high yield. 

Thioethers (sulfides) can be prepared by treatment of alkyl halides with salts of thiols (thiolate ions). The R group may be alkyl or aryl and organolithium bases can be used to deprotonate the thiol. As in 10-37, RX cannot be a tertiary halide, and sulfuric and sulfonic esters can be used instead of halides. As in the Williamson... 

Sulfur diimides react quantitatively with organolithium reagents at the sulfur centre to produce lithium sulfinimidinates of the type Li[RS(NR )2] A. The lithium derivatives may be hydrolysed by water to R NS(R)NHR which, upon treatment with MH (M=Na, K) or the metal (M=Rb, Cs) in THF, produces the heavier alkali-metal derivatives.132 The structures of these complexes are influenced by (a) the size and electronic properties of the R group, (b) the size of the alkali metal cation, and (c) solvation of the alkali-metal cation. 

The P2N4S2 ring in 111 is readily susceptible to nucleophilic attack at sulfur. Reactions with organolithium reagents give monolithium derivatives... 

The chemical behavior of heteroatom-substituted vinylcarbene complexes is similar to that of a,(3-unsaturated carbonyl compounds (Figure 2.17) [206]. It is possible to perform Michael additions [217,230], 1,4-addition of cuprates [151], additions of nucleophilic radicals [231], 1,3-dipolar cycloadditions [232,233], inter-[234-241] or intramolecular [220,242] Diels-Alder reactions, as well as Simmons-Smith- [243], sulfur ylide- [244] or diazomethane-mediated [151] cyclopropanati-ons of the vinylcarbene C-C double bond. The treatment of arylcarbene complexes with organolithium reagents ean lead via conjugate addition to substituted 1,4-cyclohexadien-6-ylidene complexes [245]. 

Y = O) or —90°C (Y = NMe, S) gave the corresponding intermediates 427 resulting from a carbon-sulfur cleavage. Further reaction of these functionalized organolithium compounds with different electrophiles at the same temperature, followed by hydrolysis with water, yielded products 428 (Scheme 120) . 

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