Nitroalkanes formation

The above are examples of the Claisen - Schmidt reaction. The formation of p-nitrostyrenes by reaction of nitroalkanes with aromatic aldehydes in the presence of aqueous alkali may be included under the Claisen- hmidt condensation ... 

Oxidadve cross-conphng reactions of alkylated derivatives of activated CH compounds, such as malonic esters, acetylacetone, cyanoacetates, and ceitain ketones, v/ithnitroalkanes promoted by silver nitrate or iodine lead to the formation of the nitroalkylated products. This is an alternative way of performing Spj l reactions using cr.-halo-nitroalkanes. 

A proof for the formation of alkyl radicals was found by their addition to the aci-nitromethane anion (CH2=N02 ) and by their reaction with p-benzoquinone to give the optically active nitroalkane radical-anion and the semiquinone radicals, respectively. In the case of di-r-butyl sulfoxide the f-butyl radical was observed directly by its absorption spectra. 

The base-catalyzed reaction of nitroalkanes and sugar-based aldehydes (the Henry reaction) is one of the most common procedures for the lengthening of the carbon skeleton of a carbohydrate.16 The mild reaction conditions required for the formation of C C bonds by this method are usually compatible with most of the protective groups and masked functionalities involved in multistep synthesis from sugars.17... 

Internal DCR of Nitroaldol Libraries (Scheme 6.10) [5,6] iDCR was demonstrated by using a conceptual nitroaldol library including five benzaldehyde derivatives (24,36, and 47-49) and one nitroalkane (50, DCL-F, Scheme 6.11). The benzaldehydes, all with a unique substitution pattern, were selected in order to make analysis clear and simple. However, one of the henzaldehydes contained a cyano functionality in the 2-position (49), deliberately making it a candidate for subsequent tandem cyclization following nitroalcohol formation. 5-exo-dig type cyclizations of hydrox-ynitriles to the corresponding iminolactones are expected [40,41], albeit unexplored [42 5], intramolecular transformations, which in this case could lead to possible kinetic resolution of the library. 

Primary alkyl iodides and bromides are excellent substrates for the Victor Meyer reaction, providing a route to both substituted and unsubstituted nitroalkanes (Table i. i).63,65,70,7i formation of the corresponding nitrite ester is a side-reaction and so the nitroalkane is usually isolated by distillation when possible. The reaction of primary alkyl chlorides with silver nitrite is too slow to be synthetically useful. Secondary alkyl halides and substrates with branching on... 

Kaplan and Shechter found that certain oxidants react with the nitronate salts of secondary nitroalkanes to yield vic-dinitroalkanes (111) in a reaction referred to as oxidative dimerization. These reactions are believed to involve transfer of an electron from the secondary alkyl nitronate to the oxidant with the production of a nitroalkyl radical. The radical can then dimerize to the corresponding vtc-dinitroalkane (111) (Equation 1.2) or lose nitric oxide to form a ketone via the Nef reaction (Equation 1.3). Unfortunately, formation of the ketone is a major side-reaction during oxidative dimerization and is often the major product. 

Some 1,3-dinitroalkanes (145) have been synthesized from the reaction of nitroalkanes with a-nitroalkenes (144) generated in situ from the decomposition of Mannich bases (143) derived from primary nitroalkanes. Reported yields for these reactions are low and the formation of by-products limits the feasibility of the method. 

In a series of reports between 1991 and 1997 Yamaguchi showed that rubidium salts of L-proline (9) catalysed the conjugate addition of both nitroalkanes [29, 30] andmalonates [31-33] to prochiral a,p-unsaturated carbonyl compounds in up to 88% ee (Scheme 1). Rationalisation of the selectivities observed involved initial formation of an iminium ion between the secondary amine of the catalyst and the a,p-unsaturated carbonyl substrate. Subsequent deprotonation of the nucleophile by the carboxylate and selective delivery using ion pair... 

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