Ionic Denitration

Although this method is not a general procedure, being specific for a-nitroketones, it has several merits to avoid the use of toxic reagents such as organotin compounds. Functionalized ketones have been prepared by this denitration reaction, in which functionalized nitroalkanes are used as alkyl anion synthons. For example, 3-nitropropanal ethylene acetal can be used as synthon of the 3-oxo-propyl anion and 1,4-dicarbonyl compounds are prepared, as shown in Eq. 7.88.135 

The simultaneous denitration-deoxygenation of a-nitroketones is performed on treatment with TsNHNH2 and NaBH4 at 80 °C to give alkanes (Eq. 7.90).137 

The nitro groups in Eqs. 7.88-7.90 are readily replaced by hydrogen with tin hydride under radical conditions as discussed already. However, the nitro groups in the a-nitrosulfides or (3-nitrosulfides are not replaced by hydrogen on treatment with tin hydride but the reaction affords desulfonated products (Eq. 7.51) and alkenes (Eq. 7.97) such radical elimination reactions are discussed in Section 7.3.1. (see Eqs. 7.91 and 7.92).138 

The nitro groups of a- or [i-nitrosulfides are cleanly replaced by hydrogen via ionic hydrogenation to give sulfides, as shown in Eqs. 7.93-7.95. The attack of hydride takes place at the more substituted carbon.139 

The difficulty in controlling the regiochemistry during radical-denitration of allylic nitro compounds is well known. The migration of the double bond is a serious problem, as shown in Eq. 7.96. This problem is overcome by a hydride transfer reaction in the presence of a palladium catalyst (Eq. 7.97).140 

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SRV1 reactions of gem-halonitroalkanes with the anion of active methylene compounds followed by deethoxycarbonylation and denitration provide useful methods for preparing highly substituted olefins, as shown in Eq. 7.140.186 Because the SRN I reaction is less sensitive to steric effects than the ionic reaction, such reaction as that shown in Eq. 7.140 has merits over other... 

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