Sulfur Ylides and Related Nucleophiles

For example, the Grignard reagent derived from chloromethyltrimethylsilane adds to an aldehyde or ketone and the intermediate can be converted to a terminal alkene by base.  

Sulfur ylides are next to phosphorus ylides in importance as synthetic reagents. Dimethylsulfonium methylide and dimethylsulfoxonium methylide are especially useful. These sulfur ylides are prepared by deprotonation of the corresponding sulfonium salts, both of which are commercially available. 

There is an important difference between the reactions of these sulfur ylides and those of phosphorus ylides. Whereas phosphorus ylides normally react with carbonyl compounds to give alkenes, dimethylsulfonium methylide and dimethylsulfoxonium methylide yield epoxides. Instead of a four-center elimination, the adducts 

Trost and L. S. Melvin, Jr., Sulfur Ylides, Academic Press, New York, 1975 E. Block, Reactions of Organosulfur Compounds, Academic Press, New York, 1978. 

CHAPTER 2 REACTIONS OF CARBON NUCLEOPHILES WITH CARBONYL GROUPS 

Reactions of Carbon Nucleophiles with Carbonyl Compounds 

With the more stable dimethylsulfoxonium methylide, the reversal is relatively more rapid and product formation takes place only after conjugate addition. 

Another difference between dimethylsulfonium methylide and dimethylsulfoxonium methylide concerns the stereoselectivity in formation of epoxides from cyclohexanones. Dimethylsulfonium methylide usually adds from the axial direction whereas dimethylsulfoxonium methylide favors the equatorial direction. This result may also be due to reversibility of addition in the case of the sulfoxonium methylide.169 The product from the sulfonium ylide would be the result of the kinetic preference for axial addition by small nucleophiles (see Part A, Section 3.10). In the case of reversible addition of the sulfoxonium ylide, product structure would be determined by the rate of displacement, and this may be faster for the more stable epoxide. 

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SECTION 2.7. SULFUR YLIDES AND RELATED SPECIES AS NUCLEOPHILES... 

Closely related with the synthesis of ylides from carbenes is the use of ylides as carbene transfer reagents (CTR), that is processes in which the ylide is cleaved homolytically, liberating the nucleophile and the carbene, which could remain both coordinated to the metal or not (Scheme 10). Diphosphirane (34) can be obtained from the diphosphene by reaction with sulfur ylide Me2S(0)=CH2, which behave as a carrier of the CH2 unit [95]. Recent work of Milstein et al. shows that sulfur ylides decompose in the presence of Rh derivatives with vacant coordination sites affording Rh(l)-carbene complexes [96, 97]. Complexes (35-37) can be obtained from... 

The high nucleophilicity of a-selenoalkyllithiums towards carbonyl conqiounds, even those that are the most hindered or enolizable, such as 2,2,6-trimethyl- and 2,2,6,6-tetramethyl-cyclohexanone (Schemes 113 and 164), di-t-butyl ketone, pennethylcyclobutanone, peimethylcyclopenta-none (Schemes 113 and 187) °- and deoxybenzoin (Schemes 115, 116 and i65y 4 49 23 iqws the synthesis of related alkenes, epoxides and rearranged ketones which are not available from the same carbonyl compounds on reaction with phosphorus or sulfur ylides - or diazoalkanes. ... 

The formation of desaurins from ketones, carbon disulfide, and base 1275,1281,1282,1285-1290 believed to involve nucleophilic attack on a thioketene by the dianion of a 1,1-dimercaptoalkene, as shown for the synthesis of 572. Related syntheses involve the use of thiophosgene instead of carbon disulfide and the use of diazoalkanes or phosphonium and sulfonium ylides instead of a ketone and base. Treatment of perfluoroiso-butylene with fluoride ion and elemental sulfur in a dipolar, aprotic solvent ° °° or with sources of anionic sulfur (potassium sulfide, sodium hydrosulfide,potassium thiocyanate,sodium thiosulfate, dithiocarbamate salts, dithiophosphate salts ) give the dimer (573) of bis(trifIuoromethyl)-thioketene. Similarly, other 2,4-bis(methylene)-l,4-dithietanes are obtained by treating 2,2-dichlorovinyl ketones with anionic sulfur re-... 

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