Organic nitroaldol reactions

The compound 3 can be easily prepared, in one pot, through a solvent-free procedure by nitroaldol reaction of nitroalkane 1 (2.2 mmol) and aldehyde 2 (2.2 mmol, freshly distilled), on activated neutral alumina (0.6 g, the alumina was added to a mechanically stirred solution of 1 and 2, at 0°C, then at room temperature for 20 h). Then, in situ addition (0°C) of wet-alumina supported chro-mium(VI) oxide (0.88 g (8.8 mmol) of C1O3 and 2.64 g of wet alumina). After standing for additional 20 h, the product was extracted with diethyl ether and passed through a bed of alumina. Evaporation of the organic solvent and flash chromatographic purification afforded the pure a-nitro ketone 3 in good yields (68-86%). 

Rosini, G. 1991. The Henry (nitroaldol) reaction. In Comprehensive Organic Synthesis. Trost, B.M., ed. Pergamon Press, Oxford, vol. 2, pp. 321 0. 

For example, an effective procedure for the synthesis of LLB (where LL = lanthanum and lithium) is treatment of LaCls 7H2O with 2.7 mol equiv. BINOL dilithium salt, and NaO-t-Bu (0.3 mol equiv.) in THF at 50 °C for 50 h. Another efficient procedure for the preparation of LLB starts from La(0-/-Pr)3 [54], the exposure of which to 3 mol equiv. BINOL in THF is followed by addition of butyllithium (3 mol equiv.) at 0 C. It is worthy of note that heterobimetallic asymmetric complexes which include LLB are stable in organic solvents such as THF, CH2CI2 and toluene which contain small amounts of water, and are also insensitive to oxygen. These heterobimetallic complexes can, by choice of suitable rare earth and alkali metals, be used to promote a variety of efficient asymmetric reactions, for example nitroaldol, aldol, Michael, nitro-Mannich-type, hydrophosphonylation, hydrophosphination, protonation and Diels-Alder reactions. A catalytic asymmetric nitroaldol reaction, a direct catalytic asymmetric aldol reaction, and a catalytic asymmetric nitro-Mannich-type reaction are discussed in detail below. 

Fig. 23.3 Acid/base catalyst from the Iwasawa group, containing organic amines tethered to acidic sihca-alumina. This material was found to catalyze the cyano-ethoxycarbonylation (best when R = Me) and nitroaldol reaction (best when R=H) of benzaldehyde [10]...

Nanostructured heterogeneous catalysts were prepared by supporting amines on silica-alumina materials (SA-NR2) via post-modification methodology. The promising adjacent position of acid and base sites on the SA-NR2 allowed high catalytic activity for various organic transformations such as cyanoethoxycarbonylation (Scheme 3.38 route a) and the nitroaldol reaction (Scheme 3.38 route b). ... 

GENERAL CONSIDERATIONS ON THE NITROALDOL REACTION AND ITS UTILITY IN ORGANIC 322 SYNTHESIS... 

The utilization of carbanions stabilized by various electron-withdrawing groups to effect carbon-carbon bond formation occupies a central position in organic synthesis. This chapter focuses on the reactions of nitro-stabilized carbanions (nitronate anions or their equivalents) with aldehydes and ketones. This route for the coupling of a carbonyl and a nitroalkane component, leading to vicinal nitro alcohols, was discovered in 1895 by Henry and is currently known as the Henry or nitroaldol reaction. 

The preparation of 2-nitro alcohols was also achieved by reaction of equimolar amounts of nitroal-kanes and aldehydes in the presence of alumina-supported potassium fluoride without solvent (equation 12). A peculiar feature of diis method were reactions performed with aromatic aldehydes, such as benz-aldehyde and furaldehyde, which allowed preparation of the corresponding 2-nitro alcohols without dehydration of these into nitroalkenes, as observed when nitroaldol reactions were performed with organic bases in homogeneous medium or with alumina alone. 

The nucleophilic addition of a nitroalkane to a carbonyl group, referred to as the nitroaldol or Henry reaction, is a very powerful C-C bondforming reaction of great tradition and with numerous applications in synthetic organic chemistry [36-39], Moreover, the diversity of further... 

The nitroaldol (Henry) reaction constitutes a powerful C-C bond-forming process in organic chemistry, providing efficient access to valuable functionalized organic compounds such as 1,2-amino-alcohols, a-hydroxy-carboxylic acids and 3-hydroxy-nitroalkanes [215, 216]. 

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