Sulfur-containing ylides

Similaf considerations apply to the sulfonium and sulfoxonium ylides. These ylides are formed by deprotonation of the corresponding positively charged sulfur-containing cations. 

From the results with the isolable ylides 350, it can be concluded that the fate of less stable, non-isolated sulfonium ylides depends dramatically on their respective substituents 336,338). Thus, the outcome of these reactions is programmed at the ylide stage and not during interaction of a presumed metal carbene with the sulfur-containing substrate. 

In comparison with other 1,3-dipoles that have been extensively explored in organic synthesis (7), sulfur-centered 1,3-dipoles (1-4) are rather uncommon species. However, within the last two decades, remarkable progress has been made regarding both methods of generation and synthetic applications. In particular, thiocarbonyl ylides (1) were established as key intermediates useful for the preparation of sulfur-containing heterocyclic compounds. General methods for the preparation of thiocarbonyl ylides and their chemical reactivity have been reviewed (8-11). 

Two types of sulfur-containing five-membered heterocycles are convenient precursors of thiocarbonyl ylides, namely, 2,5-dihydro-1,3,4-thiadiazoles (20) and l,3-oxathiolan-5-ones (21) (Scheme 5.5). The precursors 20 are accessible by two different methods. 

Carbene cyclization reactions offer a convenient and efficient method for the synthesis of five-membered sulfur-containing rings. These may involve both carbene insertion into a C—H bond and ylide formation. 

Free carbene 429 generated by photolysis or thermolysis of the diazo compound cyclizes into the sulfonium ylide, which undergoes a thia-Stevens rearrangement to 430 in 19% yield. The same result was obtained using the corresponding p-tosylhydrazone sodium salt as a carbene precursor (83JA6096). Rh(II)-catalyzed decomposition of sulfur-containing diazo... 

Recently, the known method for the synthesis of thiolanes by cyclization of diazo ketosulfides (72CC860) has received further development (92TL169 95JOC53). It was found that sulfur-containing a-diazo ketones 437 bearing a tethered alkyne unit decomposed in the presence of Rh2(OAc)4 via the addition of the rhodium-stabilized carbenoid onto the acetylene jr-bond to give a vinyl carbenoid, followed by sulfonium ylide formation and a subsequent [2,3]- or [l,2]-sigmatropic shift. This transfor-... 

Yamamoto, M., Kakinuma, M., Kohmoto, S., Yamada, K. Sommelet-Hauser rearrangement of oxygen- and sulfur-containing heteroaramatic sulfonium ylides. Bull. Chem. Soc. Jpn. 1989, 62, 958-960. 

Similar considerations apply to the sulfoxonium and sulfonium ylides, which are formed by deprotonation of the corresponding positively charged sulfur-containing cations. The additional electronegative oxygen atom in the sulfoxonium salts stabilizes these ylides considerably, relative to the sulfonium ylides. ... 

Like thiophene, selenophene derivatives react with dimethyl diazomalonate in the presence of rhodium acetate to give ylides (17) which are less stable than their sulfur-containing congeners <84CS253>. 

A chiral selenophosphoramide catalyst was employed for the intramolecular cyclization of an alkenyl sulfonamide to achieve the enantioselective formation of N-heterocycles including an azepane derivative via a mechanism proposed to include formation of a three-membered sulfur-containing ring (14JA8915). A [4 + 3]-cycloaddition reaction of methyl coumalate 12 with an azomethine ylide, formed from imine esters 13 yielded functionalized azepine derivatives 14 (14OL4508). 

Sulfur ylides contain a carbanion, which is stabilizea oy an adjacent positively-charged sulfur. Ylides derived from alkylsulfonium salts are usually generated and utilized at low temperatures. Oxosulfonium ylides are, however, stable near room temperature. The most common method of ylide formation is deprotonation of a sulfonium salt. What has been said... 

Previously, the same author [52] reported that compounds containing the tricoordinated sulfur cation, such as the triphenylsulfonium salt, worked as effective initiators in the free radical polymerization of MMA and styrene [52]. Because of the structural similarity of sulfonium salt and ylide, diphenyloxosulfonium bis-(me-thoxycarbonyl) methylide (POSY) (Scheme 28), which contains a tetracoordinated sulfur cation, was used as a photoinitiator by Kondo et al. [63] for the polymerization of MMA and styrene. The photopolymerization was carried out with a high-pressure mercury lamp the orders of reaction with respect to [POSY] and [MMA] were 0.5 and 1.0, respectively, as expected for radical polymerization. 

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