Sulfoxonium ylides compounds

Stability of both the parent system and the S- oxide is conferred by the presence of electron-withdrawing substituents on the carbon framework, especially at positions 2, 4 and 6, while electron-donating substituents on sulfur also help. Compounds (48), (49) and (50) illustrate these conclusions, as they are air-stable, isolable species (74CL1101). Exactly analogous factors acting on stability are seen with acyclic sulfonium and sulfoxonium ylide compounds. 

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. 

Fig. 9.5. Comparison of sulfonium and sulfoxonium ylides II—chemoselectivity in the reaction with an a,/3-unsaturated carbonyl compound. The sulfoxonium ylide reacts through the enolate intermediate A, whereas the sulfonium ylide reacts through the alkoxide intermediate B.

Unstabilized sulfonium ylides and stabilized sulfoxonium ylides show different reactions with a,P-unsaturated carbonyl compounds the former give epoxides and the latter give cyclopropanes. The epoxide formation (i.e. 1,2-addition) is kinetically favourable while cyclopropane formation (i.e. 1,4-addition, Michael addition) is energetically favourable. 

Sulfurylides as methylene transfer reagents were not suitable in every case. Sulfoxonium ylide (178) and the pyridyl derivative (164, R= pyridyl) formed the cyclopropane (176) , but the same reagent generated an acylated sulfoxonium ylide (177) with a phenyl compound (164, R = phenyl) (Scheme 2). The less reactive sulfonium ylide (179) and... 

Sulfoxonium ylides are useful in the preparation of cyclopropane derivatives by reaction with a,p-unsaturated carbonyl compounds (see Chapter 10, p. 189). Sulfoxonium salts (26) are intermediates in the Moffatt oxidation (Scheme 15a) (see Chapter 5, p. 66), and they also undergo several other useful reactions (Schemes 15b-15d). The Pummerer rearrangement involves an oxosulfonium ylide intermediate (see Chapter 5, p. 68). 

The two types of sulfur ylides also differ in their reactions with a,p-unsaturated carbonyl compounds. The highly reactive sulfonium ylides react rapidly by 1,2-addition across the carbon-oxygen double bond to yield the epoxides. On the other hand, the less reactive sulfoxonium ylides react by slower conjugate addition (1,4-addition) to give substituted ketocyclopropanes. Thus, dimethylsulfonium methylide (21) reacts rapidly with benzylideneacetophenone (chalcone) (37)... 

Osmacycle (48) arises from an alkyl osmium compound by a complex thermal rearrangement which has been studied in detail (Equation (19)) <86JAI346, 90JA704). A phosphonium-platinacyclopropane arises by intramolecular addition to an alkene (Equation (20)) <90OMl2ll>. Metallacycles are also available by addition of a sulfoxonium ylide to a metal-phosphorus double bond (Equation (21)) <90CB739>. 

Further methodology for the construction of precursors for 1,2 3,4] Cope rearrangements is the cyclopropanation of a,/i-unsalurated carbonyl compounds with sulfoxonium ylides, followed by Wittig reaction, e.g., formation of g8S6g-870... 

Not only compounds with thioalkyl groups, but also those with aliphatic or aromatic sulfine groups react intramolecularly with carbenoid groups, as the examples in Schemes 8-63 and 8-64 demonstrate (Moody et al., 1988). In these reactions, cyclic sulfoxonium ylides are obtained. 

Ide, J., and Y. Kishida The Formation of some stable Sulfoxonium-Ylides from Acetylenic Compounds and some further Reactions of these stable Ylides. Tetrahedron Letters (London) 76, 1787 (1966). 

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... 

The greater stability of sulfoxonium compared to sulfonium ylides and the associated consequence that product-development control influences, which of several conceivable zwitterionic intermediates is formed preferentially, is also noticeable in reactions of S ylides with a,/3-unsaturated carbonyl compounds. This can be seen in Figure 9.5 using the example of two reactions with cyclohexenone. Because of product-... 

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