Sulfoxides, aryl with Grignard reagents

In constrat to a-halo-/3-ketosulfoxides, I-chloroalkyl aryl sulfoxides react with Grignard reagents to give /3-oxido carbenoids. The rearrangement of these intermediates leads... 

Many ligand-coupling reactions occurring via s-sulfurane intermediates involve treatment of aryl or heteroaryl sulfoxides with Grignard reagents (Scheme 14). The intramolecular nature of the ligand coupling reaction is demonstrated by the absence of cross-over products thus, the formation of 2-benzylpyridine (43) (Scheme 14a) may proceed as shown in Scheme 15. 

Spry has reported that cis-P-halo-a,P-unsaturated sulfoxides, on treatment with Grignard reagents, react to form carbon-sulfur bonds, and has used this methodology as part of the preparation of 5(l)-C(2)-secocephems [70], while Posner found that a,P-unsaturated aryl sulfoxides were easily reduced to the corresponding sulfides upon treatment with ethylmagnesium bromide/10% cuprous iodide with retention of double bond stereochemistry [71]. 

Sulfides, or thioethers, are sulfur analogues of ethers, and like ethers they can be either symmetrical (R2S) or unsymmetrical (RSR1, where R and R are different). Sulfides can be prepared from alkyl halides by a Williamson-type synthesis with sodium hydrogen sulfide, sodium thiolate or sodium sulfide from alkyl or aryl halides via the Grignard reagent (11) from alkenes by radical-catalysed addition of thiols or by reduction of sulfoxides (Scheme 9).2b... 

Reaction with organosulfur compounds. Perfluoroketene dithioacetals arise from perfluoroalkanedithiocarboxylic esters by attack of Grignard reagents on the doubly bonded sulfur atom, whereas 1-haloalkenyl aryl sulfoxides form a-haloalkenylmagnesium halides. ... 

It is known that on treatment of alkyl aryl sulfoxide 1 with alkylmetal (alkyl-lithium or Grignard reagent) sulfur-aryl (path a) or sulfur-alkyl (path b) bond cleavage occurs to give arylmetal 2 or alkylmetal 3 (Scheme 3.9). This reaction is commonly called the hgand exchange reaction of sulfoxides. Although the predominant path of this reaction depends on the structure of the sulfoxide 1, this dependence remains somewhat obscure at present. 

The reaction of -thionyldiimidazole with aryl Grignard reagents is a standard procedure for the synthesis of symmetrical sulfoxides. when applied to thienyllithium, a high yield (84%) of the ligand coupling product (193) was serendipitously obtained instead of the expected di(2-thienyl) sulfoxide. 

Previously, Andersen et al. had attempted to prepare sulfuranes from the reactions of diaryl sulfoxides with aryl Grignard reagents and aryl lithium agents. They reported that the reactions give initially the corresponding triaryl sulfoni-um salts, from which two pathways, namely the formation of tetraaryl sulfuranes and the formation of benzyne, take place simultaneously, on the basis that they obtained diaryl sulfides and biaryls derived from benzyne, as shown in Scheme 7 [37]. 

Upon treatment with alkyl or aryl Grignard reagents, the corresponding methyl alkyl or aryl sulfoxides are obtained with high enantiomeric purity (Scheme 2.6, Table 2.2), albeit in low yields. 

Other Applications. Thionyl chloride has been used to convert epoxides to vicinal dichlorides and for the preparation of dialkyl sulfides from Grignard reagents. Phenols react with SOCI2 to produce aryl chlorosulfites and diaryl sulfites or nuclear substitution products. As shown in eq 14, Aluminum Chloride catalysis yields symmetric sulfoxides, while in the absence of Lewis acids, aromatic thiosulfonates are the principal products. Primary amines, especially aromatic ones, react with SOCI2 to produce N-sulfiny lamines, which are potent enophiles and useful precursors to some heterocyclic compounds. ... 

Likewise, the sulfoxide-metal exchange reaction of /3-acetoxy sulfoxides 164 (/3-mesyloxy sulfoxides can also be used), which are prepared from alkenyl aryl sulfoxides 163 and aromatic aldehydes, with a Grignard or alkyllithium reagent at low temperatures gives the allenes 162 in good to excellent yield (Scheme 5.24) [65],... 

Finally, the sulfinates were transformed to o.p. sulfoxides by treatment with either Grignard or organolithium reagents. The presence of a free hydroxyl group in the sulfmate esters involves the use of two molar equivalents of the organometallic in THF at room temperature. Various dialkyl, alkyl aryl, and diaryl sulfoxides have been obtained in quantitative yield and in 100% ee (Table 12). 

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