Oximes dianions

Aminoisoxazoles 22 have been synthesized by nucleophilic addition of lithiated alkyl nitriles to a-chloroximes <06OL3679>. The cyclization of oxime dianions with diethyl oxalate afforded isoxazole-5-carboxylates 23 by acid-mediated dehydration of intermediate hydroxyisoxazolines <06S2515>. 

A total synthesis of the sesquiterpene ( )-illudin C 420 has been described. The tricyclic ring system of the natural product is readily quickly assembled from cyclopropane and cyclopentene precursors via a novel oxime dianion coupling reaction and a subsequent intramolecular nitrile oxide—olefin cycloaddition (463). 

Substituted 5-alkylisoxazoles 203 are successfully obtained from oxime dianions, prepared from acetone oxime 202 and BuLi, and then by interaction with Af-methoxyamides of type RCON(OMe)Me (equation 88) . ... 

Another resonance-stabilized species discussed here is nitrosamine anions, whose chemistry has been reviewed several times.Cyclic nitrosamines normally lose the axial proton syn to the nitrosamine oxygen, and alkylate by axial approach of the electrophile. In these respects, nitrosamine anions are similar to their isoelectronic counterparts, oxime dianions, as shown in equation (4). ... 

Many of the same features of imine and imine anion structure previously discussed (Section 4.1.3.2) are apparent with hydrazones and their anions and with oxime ether anions. A number of investigations of the structure of A A -dialkylhydrazone and oxime ether anions as well as oxime dianions have been carried out. Most notable are the experimental studies of Collum and Clardy, " and the theoretical treatment by Glaser and Streitwieser. As might be expected, and as was observed for lithiated imine anions iyida supra), lithiated hydrazones exist in the solid as aggregates, with two lithiums coordinated to the aza anion system (Figure 3). ... 

The similar endo(B)-exo cyclizations have been effected with phosphorus pentoxide and more recently with trimethylsilyl polyphosphate (equation 32 and 33). The starting alkenic oximes are readily obtainable by the alkylation of the oxime dianion. Hence the overall process provides convenient access to the stereospecific synthesis of various heterocycles bearing substituents in the desired positions. 

Thus the nitrosamine anion is a resonance-stabilized species in which the carbanionic lone pair overlaps the TT-system of the nitrosamine. By contrast, the amide anion is a dipole-stabilized species in which the lone pair remains in or near the nodal plane of the amide n -system. Given the similarity of the two systems, this difference in behavior is striking. Although the geometry observed in nitrosamine anion alkylations is similar to that of their isoelectronic counterparts, oxime dianions,it is puzzling that amide anions differ, since they are also isoelectronic, as shown in Figure 1. 

Continuing their work on 1,4-dianions of phenylhydrazone, Hauser and coworkers inspected similar reactions with the 1,4-oxime dianions . Acetophenone oxime gave the dilithium salt in reaction with r-BuLi and underwent C-alkylation with benzyl chloride and dialkylation with 1,4-dibromobutane (equation 32). 

Jung and coworkers reported an exclusive regioselectivity in alkylation reactions of the dianionic oxime ketone. They showed that a primary or secondary oxime undergoes lithiation when reacting with two equivalents of /-BuLi for 15 min at 0 °C only when it has a syn geometry. Oxime dianion with an anti configuration is formed after a long time, and in a very low yield (equation 35). 

Because previous investigations showed that there is no syn-anti isomerization in oxime dianions , in contrast to dimethylhydrazone anion where a syn-anti mixture gives after lithiation only one (jy/i) monoanion, Ensley and Lohr checked the ability of the oxime ether to undergo isomerization of this type. An E and Z mixture of the 2-heptanone tetrahydropyranyl oxime gave, after lithiation and reaction with acetone, a substitution product only on the methyl group (equation 41). 

Nucleophilic attack by an oxime dianion on the oxazinone 284 gives an enaminone intermediate 285, which spontaneously cyclizes to an isoxazole 286, Scheme 78 (89H1443). In some cases, depending on the oxime substituents, pyridine N-oxides are the sole products (Section VI,B,3). 

Reaction of phenylhydrazone and oxime dianions with one equivalent of alkyl halide (137) takes place at the carbon. 

The formation of pyrroles 54 and 57 is likely to be a result of decomposition of the oximes 55 and 59 in the form of dianion by analogy with retroaldol condensation (Scheme 33). As far as the formation of pyrrole 57 (Schemes 28 and 29) is concerned, this seems to result from -elimination of water and vinyl alcohol molecules from the oximes 55 and 58 respectively or from the corresponding intermediate 2-hydroxy(vinyloxy)propyl-1-vinylpyrroles. 

The difference in the deprotonation rate of anti and syn oximes, the much higher kinetic acidity of the primary or secondary syn hydrogens than the primary anti hydrogens, and the fact that the anti dianion, in spite of the favorable deprotonation... 

Reaction of benzoin-a-oxime with sodium hydride in propan-2-ol produces 1,5-dianion which is further cyclized into 1,5,6-dioxazocine ring system with 1,3-dibromopropane (Equation 29 <2004S837>). 

Stable dioxadiazasilepines and dioxadiazastannapines 216 were prepared in 60-77% yields from vicinal oximes 215 via dianion intermediates, which are intramolecularly trapped with dielectrophilic diorganodichlorosilanes and diorganodichlorostannanes, respectively (Equation 43) <2005TL315>. 

The dianions of (Z)-oximes react with aldehydes and ketones to give -hydroxy oximes in good to very good yields (Scheme IS) - no dianion formation occurs with ( )-aldoximes. 

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