Cyclopropanes from sulfoxonium ylides

Both S ylides from Figure 9.1 react with a,/3-unsaturated esters to give cyclopropanes (Section 9.2). Sulfoxonium ylides also react with a,j8-unsaturated carbonyl compounds to give cyclopropanes (Section 9.2). Sulfonium ylides cannot do this because they react to form epoxides. 

The copper-catalyzed methylene transfer from sulfonium ylidcs to electron-rich olefins proceeds stereospecifically and probably involves a methylene copper complex15. Sulfonium, sulfoxonium, and (dialkylamino)sulfoxonium ylides are nucleophilic species and, in uncatalyzed reactions, only good Michael acceptors are attacked16 (see also Vol. IV/3, p 139 and Vol. E 11 2, p 1422). The cyclopropanation proceeds stepwise via a zwitterion, and therefore the olefin configuration is not necessarily reflected in the cyclopropane stereochemistry. Thus, both dimethyl ( )- or (Z)-2-butenedioate react with dimethylamino(phenyl)sulfoxonium methylide to give the //ww-substituted cyclopropane 4 only1. ... 

Kaiser, C., B. M. Trost, J. Beeson, and J, Weinstock Preparation of Some Cyclopropanes and Stable Sulfoxonium Ylides from Dimethyl-sulfoxonium Methylide. J. Org. Chem. 30, 3972 (1965). 

Dimethylsulfonium methylide and dimethylsulfoxonium methylide also differ in their reachons with a,p-unsaturated carbonyl compounds. The sulfonium ylide reacts at the carbonyl group to form an epoxide, but with the sulfoxonium ylide a cyclopropane derivative is obtained by Michael addihon to the carbon-carbon double bond. The difference is again due to the fact that the kinehcally favoured reachon of the sulfonium yhde with the carbonyl group is irreversible, whereas the corresponding reaction with the sulfoxonium yhde is reversible, allowing preferenhal formahon of the thermodynamically more stable product from the Michael addihon. For example, the cyclopropane 112 is obtained from the reaction of dimethylsulfoxonium methylide with the enone 111 (1.105). Other methods for the formahon of cyclopropanes include carbene and Simmons-Smith-type... 

MacMillan has employed sulfoxonium ylides, such as 130, derived from phenacyl bromides, in enantioselective cyclopropanation of enals (Equation 21) [80]. Treatment of hexenal (129) with 130 in the presence of 20 mol % of catalyst 131 afforded adduct 134 in 95% ee, dr=30 l, and 85% yield. The fact that unsaturated aldehydes could be used as substrates in these reactions is impressive, especially given the propensity of aldehydes to otherwise undergo epoxide formation. The system owes its success to the unique ability of the substrate enals to reversibly form the corresponding iminium ions 132, which display enhanced electrophilicity towards the reagent ylide (cf 133). 

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