Sulfur, reaction with organolithium compounds

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) . 

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). 

Reductive 1,2-eIimination of chlorine and bromine from adducts of l-bromo-2-chlorocyclo-propene (see Section 5.2.2.1.2.5.) with oxygen and sulfur hetarenes has served in the synthesis of a number of cycloproparenes. This transformation is effected by low-valent titanium together with lithium aluminum hydride or an organolithium compound. Thus, reaction of the adduct 3 of l-bromo-2-chlorocyclopropene and 1,3-diphenylisobenzofuran with tita-nium(III) chloride and lithium aluminum hydride overnight in tetrahydrofuran led to elimination of both halogens together with extrusion of the oxygen and formation of 2,7-diphenyl-l/f-cyclopropa[ ]naphthalene (4) in 72% yield. 

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]) ... 

The reaction of polymeric organolithium compounds with thiir-anes is reported to be a viable route for the preparation of thiol-functionalized polymers. However, until recently the mechanism of this reaction had not been elucidated, that is, whether this proceeds via a sulfur extmsion reaction (path (a) in Scheme 11) or via a ring-opening reaction (path (b) in Scheme 11). For simple alkyllithium compounds, the sulfur extmsion pathway has been shown to be operative. 

Different alcohols and protected alcohols (as hemiacetals, silyl, methoxymethyl or phenyl ethers) were lithiated at the d-position to give the corresponding organolithium compounds. In the case of alcohols, a previous deprotonation of the hydroxyl functionality is required. The chiral intermediate 197 was prepared from the phenylsulfanyl derivative 196 first by deprotonation followed by carbon-sulfur bond cleavage with LiDTBB at low temperature. The reaction of the dianionic system 197 with y- and d-lactones in the presence of cerium(III) salts gave, after hydrolysis, spiroketal pheromones 198 (Scheme 2.27) [163]. 

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. 

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