Amides carbonyl ylide derivation

Carbonyl Ylides Derived from Amides and Ureas. 

Carbonyl ylides derived from nitrogen-substituted carbonyl moieties provided for the synthesis of very stable push-pull dipolar intermediates. Although these compounds are quite stable, they still have sufficient reactivity to engage in cycloaddition and related processes. Carbonyl ylides derived from amides have been trapped in intermolecular cycloadditions to give aminals (Scheme 4.34) (56). 

The Rh(II)-catalyzed reaction of pyridone 96 with DMAD was also found to give cycloadducts derived from an intermediate azomethine ylide. The initial reaction involves generation of the expected carbonyl ylide by intramolecular cyclization of the keto carbenoid onto the oxygen atom of the amide group. A subsequent proton shift generates the thermodynamically more stable azomethine ylide, which is trapped by DMAD. This is an example of subsequent formation of ylides of two types, a phenomenon termed a dipole cascade (93JOC1144). 

Cyclic carbonyl ylides, formed from diazo amides or diazo anhydrides through intramolecular carbene addition to the carbonyl group, react with the triple bond of a dipolarophile to produce bicyclic adducts. The latter undergo a retrodiene reaction, splitting off an alkyl isocyanate or carbon dioxide to give furan derivatives. 

Sulfur ylides are a classic reagent for the conversion of carbonyl compounds to epoxides. Chiral camphor-derived sulfur ylides have been used in the enantioselective synthesis of epoxy-amides <06JA2105>. Reaction of sulfonium salt 12 with an aldehyde and base provides the epoxide 13 in generally excellent yields. While the yield of the reaction was quite good across a variety of R groups, the enantioselectivity was variable. For example benzaldehyde provides 13 (R = Ph) in 97% ee while isobutyraldehyde provides 13 (R = i-Pr) with only 10% ee. These epoxy amides could be converted to a number of epoxide-opened... 

The phosphanes useful in this process are built from acyl derivatives of compounds such as those shown in Figure 17.22. During the Staudinger ligation process, once the azide reactant forms the aza-ylide with the phosphine, electrophilic attraction induces the nitrogen to attack the electron deficient carbonyl, which in turn causes release of the phosphonium group and forms the amide bond (Figure 17.23). 

Imino derivatives 100 of compounds of type 95 were also directly prepared from cumulated ylides 82 or 4 and parabanic acid derivatives 99 by a presumed mechanism as depicted in Scheme 22 [70]. Attack of the nucleophilic ylidic carbon atom at the most electrophilic amide-type carbonyl carbon atom, ring opening with loss of phenyl isocyanate, and recyclization by N-C bond formation are the key steps. This reaction is reminiscent of an older one, furnishing 5,5-diethoxy- l-thiobenzoyl-4-triphenylphosphoranylidene-pyrrolidine-2,3-dione 102 from 2-phenylthiazoHne-4,5-dione 101 and 4 [71] in modest yield. 

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