Nitrocyclopropyl anion

Bordwell and coworkers note that nitrocyclopropane under the conditions of exchange rapidly decomposes. Thus, the nitrocyclopropyl anion is not easily formed and is therefore very reactive, similar, for example, to cyclopropyl ethyl ester enolates (Section IV.B.l.a). 

The pK measurements are nicely supported by efforts of Seebach and coworkers to get hold of the elusive nitrocyclopropyl anion . When nitrocyclopropane was treated at temperatures between —80 and — 110°C with bases such as butyllithium, LDA or potassium hexamethyldisilylamide in THF, yellow to red solutions have been obtained which were thought to contain the lithium salt of acinitrocyclopropane (267a). Workup after any amount of time, raising the temperature, or addition of any electrophile with or without oxidizing properties, always led to the isolation of mixtures of the colorless dinitro-compound 268, and of the deep-blue nitro-nitroso compound 269. 

The question whether the nitrocyclopropyl anion might have a triplet structure (possibly similar to 271) is discussed in Section IV.B.1.1. 

Similar behaviour has been observed by Kohler and Allen and by Smith and Showell on treating the tertiary nitrocyclopropyl ketone 198 with a base. Base catalyzed stereoisomerizations of ketones like 198 had also been observed by Kohler and Smith and by Smith and ShowelP and were in agreement with the deprotonation of such cyclopropanes to the corresponding cyclopropyl anions. It thus did not seem as if the deprotonation of C(0)R-substituted cyclopropanes would cause any problems. 

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