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Ylide reactions, nonstabilized with ketones

This stabilized ylide reacts with aldehydes and ketones to furnish epoxides. The difference in reactivity between dimethylsulfonium methylide and dimethyloxosulfo-nium methylide is apparent when considering their reactions with a, 3-unsaturated ketones. Whereas the nonstabilized ylide yields the epoxide, the stabilized ylide affords a cyclopropane via conjugate addition followed by ring closure and loss of dimethyl sulfoxide. [Pg.167]

As already mentioned, ketone Wittig reactions are complicated by low carbonyl reactivity and by enolization in the case of nonstabilized ylides. The level of difficulty increases with increasing steric hindrance in the reactants, but experimental solutions are available even for the most extreme cases (159, 168-171). A discussion of the key variables is included below, partly to dispel the notion that the Wittig approach is not practical for hindered, enolizable ketones and partly to guide future stereochemical studies of the ketone reactions. [Pg.104]

Benzylidenetriphenylphosphorane (entries 8 and 9) occupies a borderline position between stabilized and nonstabilized ylides. It will react with both aldehydes and ketones. Mixtures of cis and trans-stilhene result from the reaction of benzyl-idenetriphenylphosphorane with benzaldehyde. [Pg.73]

In general, nonstabilized and semistabilized phosphonium ylides are prepared by deprotonation of the corresponding phosphonium salts with strong bases that are incompatible with aldehydes or ketones. However, some studies have shown that these phosphonium ylides can be generated in the presence of aldehydes by treatment of the corresponding phosphonium salts with a weaker base such as l,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) [100], NaOH, LiOH [101, 102], KOH [103], or K2CO3 [49, 104, 105] (Scheme 20). In addition, these bases promote the one-pot Wittig reaction of phosphonium salts with aldehydes in a number of solvents such as toluene, tetrahydrofuran, dimethyl sulfoxide, isopropanol, and water. [Pg.210]


See other pages where Ylide reactions, nonstabilized with ketones is mentioned: [Pg.486]    [Pg.422]    [Pg.466]    [Pg.757]    [Pg.373]    [Pg.757]    [Pg.95]    [Pg.757]    [Pg.553]    [Pg.209]   
See also in sourсe #XX -- [ Pg.95 ]




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Reaction with ketone

Ylide reaction

Ylides nonstabilized

Ylides reaction

Ylides reaction with

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