Ylides reactions with carbonyl compounds

In sharp contrast to the olefmation reaction employing stabilized telluronium ylides, semi-and non-stabilized ylides react with carbonyl compounds to give epoxides (like non-stabilized sulphonium and selenonium ylides). 

Similarly, Hosomi and co-workers (15) reported isothioureas as azomethine ylide equivalents. Both A-substituted and A-unsubstituted A-(trimethylsilylmethyl)-isothiourea precursors underwent cycloaddition reactions with carbonyl compounds, when treated with stoichiometric CsF to deliver a range of 2-iminooxazolidine derivatives. Typically, 63 (R = CN, R = H) furnished adduct... 

Phase transfer catalysis, or more correctly, two-phase systems, were widely applied in the synthesis of oxiranes via generation of sulfonium and sulfoxo-nium ylides and their subsequent reactions with carbonyl compounds.67... 

Current results indicate that stabilized arsonium ylides such as phenacylide, carbomethoxymethylide, cyanomethylide, fluorenylide, and cyclopentadienylide afford only olefinic products upon reaction with carbonyl compounds. Nonstabilized ylides such as ethylide afford almost exclusively epoxides or rearranged products thereof. However, semi-stabilized arsonium ylides, such as the benzylides, afford approximately equimolar amounts of olefin and epoxide. Obviously, the nature of the carbanion moiety of the arsonium ylide greatly affects the course of the reaction. It is reasonable to suppose that a two-step mechanism is involved in the reaction of heteronium (P, S, and As) ylides with carbonyl compounds (56). 

Ylides of other elements have been used much less commonly than sulfur ylides in cyclopropanations. Rather, other ylides are better known for their uses in other types of reactions, the best example being the use of phosphonium ylides in the Wittig reaction with carbonyl compounds to give alkenes. Nonetheless, some cases of cyclopropanations have been reported with phosphonium ylides and the related arsenic derivatives. Examples are given in Table 9. 

The well-known reaction of phosphorus ylides is their reaction with carbonyl compounds (aldehydes and ketones) to give alkenes. This alkenation methodology is universally known as the Wittig reaction . ... 

Reactions of Phosphonium Ylides. - 2.3.1 Reactions with Carbonyl Compounds. This year we are able to report several variations of the traditional Wittig olefination which employ the addition of catalysts to effect the reaction. For example, Lebel et al. have reported a new salt-free process for the methyl-enation of aldehydes, in which the phosphorane is generated in situ from triphenylphosphine and a diazo precursor with either a rhodium- or rhenium-based catalyst (Scheme 6). It was found that the most effective combination of catalyst and diazo-compound were Wilkinson s catalyst [RhCl(PPh3)3] and... 

Ylides may react with nitrosobenzene in a similar fashion to their reactions with carbonyl compounds (equation 12). Sulphonium ylides give nitrones phosphonium... 

Arsonium ylides were discovered near the turn of the century, but their reactions with carbonyl compounds did not become elucidated until the 1960s. In a broad sense, arsonium ylides are midway in chemical behavior between ylides of phosphorus and those of sulfur. Stabilized arsonium ylides react with carbonyl compounds to afford alkenes, whereas the unstabilized analogs give rise to epoxides. More subtly, the nature of the substituents on either the ylide arsenic or carbon atom can alter the course of the reaction the choice of solvent can exert a similar effect. ... 

Among the heavy main group elements arsenic has received the most attention. Arsonium ylides react with carbonyl compounds to yield either the alkenes or epoxides, depending upon the structure of the ylide and the reaction conditions. )espite their toxicity, arsenic compounds can be handled safely. 

Reaction with carbonyl compounds. The reagent reacts with saturated aldehydes and ketones to give an oxirane in 74-82% yield. The reaction requires about 1 -2 hrs. at temperatures of —70° to —30° and can be followed by the fading of the orange color of the ylide.1... 

Reaction with carbonyi groups. This tantalum reagent undergoes Wittig reactions with carbonyl compounds. Notably, it reacts in cases where phosphorus ylides do not (third example). 

A variety of substituted sulphonium ylides have been used in the oxiran-forming reaction with carbonyl compounds. Diphenylsulphonium-allylide (6), generated from the salt with t-butyl-lithium, afforded the expected oxiran in 80% yield upon reaction with cyclohexanone. Use of n-butyl-lithium as the generating base resulted in lower yields and contamination by the oxiran formed from a butylide, the latter probably... 

Sulphoximine ylides also have been prepared using organolithium reagents as the base, but the presence of the lithium cation changes the course of the reaction with carbonyl compounds and with conjugated... 

In a pioneering article, Farrall et al. [61] reported the preparation of fuUy regenerable sulfonium salts anchored to an insoluble polymer and their use in the preparation of epoxides by reaction of their ylides with carbonyl compounds. Their results clearly indicate that... 

The addition reaction of enolates and enols with carbonyl compounds is of broad scope and of great synthetic importance. Essentially all of the stabilized carbanions mentioned in Section 1.1 are capable of adding to carbonyl groups, in what is known as the generalized aldol reaction. Enolates of aldehydes, ketones, esters, and amides, the carbanions of nitriles and nitro compounds, as well as phosphoms- and sulfur-stabilized carbanions and ylides undergo this reaction. In the next section we emphasize the fundamental regiochemical and stereochemical aspects of the reactions of ketones and aldehydes. 

Whereas phosphonium ylides normally react with carbonyl compounds to give alkenes, dimethylsulfonium methylide and dimethylsulfoxonium methylide yield epoxides. Instead of a four-center elimination, the adducts from the sulfur ylides undergo intramolecular displacement of the sulfur substituent by oxygen. In this reaction, the sulfur substituent serves both to promote anion formation and as the leaving group. 

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