Sulfur reaction with Grignard reagents

Whereas sulfolane is relatively stable to about 220°C, above that temperature it starts to break down, presumably to sulfur dioxide and a polymeric material. Sulfolane, also stable in the presence of various chemical substances as shown in Table 2 (2), is relatively inert except toward sulfur and aluminum chloride. Despite this relative chemical inertness, sulfolane does undergo certain reactions, for example, halogenations, ting cleavage by alkah metals, ring additions catalyzed by alkah metals, reaction with Grignard reagents, and formation of weak chemical complexes. 

In all cases, the major diastereoisomer (9) is crystalline. The sulfinate esters (9a-d) undergo clean reaction with Grignard reagents to yield sulfoxides in good yield and with complete inversion of configuration at sulfur as highhghted in Scheme 2.12. 

The nickel-catalysed reaction of aryl, allyl or vinyl sulfides with Grignard reagents has been found to be an effective way for the conversion of carbon-sulfur bonds into carbon-carbon bonds [318]. However, simple aliphatic substrates are inert. 

The reaction of dithioesters with Grignard reagents is even more remarkable. Because sulfur and carbon have about the same electronegativity, the Grignard reagent may add to either end of the ji bond. If it adds to sulfur, the resulting anion is stabilized by two sulfur atoms, rather like the dithiane anions we have seen earlier in this chapter, and can be used as a d1 reagent. 

Perfluoroaryl alkyl sulfides (e.g., 7) can be synthesized by the reaction of Grignard reagents with aryl halides in the presence of elemental sulfur. For example, allyl pentalluorophenyl sulfide (7) is obtained in excellent yield from bromopentafluorobenzene (5) and allyl bromide... 

A large number of symmetrical diaryl- or dialkyl-acetaldehydes, difficult to obtain by other means, have been prepared by the reaction of ethyl ethoxyacetate, or ethyl phenoxyacetate, with Grignard reagents followed by treatment of the resulting glycol monoalkyl ether with anhydrous oxalic acid or dilute sulfuric acid. The yield in the first step is 40-80%, and the yield in the subsequent transformation is 50-80%. 

Chemically, the diazirines are remarkably unreactive and in this they contrast strongly with diazo compounds. They are unaffected by alkalies and are stable in the presence of quite strong acids. (They may be recovered unchanged from solution in lOiV sulfuric acid, though there is a slow reaction in more concentrated solutions.) They do not form complexes with inorganic cations in the way that many azo compounds do, and they are unreactive towards alcohols and dienophiles. They do, however, react with Grignard reagents to yield iV-substituted diazir-idines. 

In a related reaction sulfurated boranes (R2B-SSLR 2) react with Grignard reagents, such as methyhnagneisum bromide to give the B-alkyl borane (e.g., R2B-Me) upon heating in vacuo ... 

Thiophenethiols are prepared by reduction of the sulfonyl chlorides or, more conveniently, by the reaction of Grignard reagents or thienyllithium compounds with sulfur. They have also been obtained by cleavage or thienyl alkyl sulfides with sodium in liquid ammonia. 3-Thiophenethiol is a by-product in the commercial thiophene synthesis. Thiophenethiols have recently also been prepared by a synthesis involving Friedel-Crafts reaction of 2,4-dinitrobenzenesulfenyl chloride with thiophenes, followed by basic cleavage of the resulting sulfide. ... 

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