Nitroalkanes, reduction

One of the earliest applications of combined EPR and electrochemical measurements was the study of nitroalkane reductions [48]. Cyclic voltammetry revealed irreversible reduction waves, but some anodic peaks were observed on the reverse scan and were attributed to reaction intermediates. In situ generation produced an initial spectrum attributable to the nitroalkane anion radical, but after some time, the dialkylnitroxide spectrum was detected. This information, combined with analysis of the products formed during bulk electrolysis, suggested the following reaction sequence ... 

Higher nitroalkanes are prepared from lower primary nitroalkanes by a one-pot synthesis (69). Successive condensations with aldehydes and acylating agents are followed by reduction with sodium borohydride. Overall conversions in the 75—80% range are reported. 

Hydroxylamine can be prepared by a variety of reactions involving the reduction of nitrites, nitric acid or NO, or by the acid hydrolysis of nitroalkanes. In the conventional Raschig synthesis, an aqueous solution of NH4NO2 is reduced with HS04 /S02 at 0° to give the hydroxylamido-A ,A -disulfate anion which is then hydrolysed stepwise to hydroxylammonium sulfate ... 

Scheme 7.5. BusSnH-catalyzed reduction of nitroalkanes to alkanes...

Tri bromonitrom ethane. This article supplements the material in Vol 2, B312-L under Bromoform and Derivatives CA Registry No 464-10-8. The IR and UV spectra are given in Ref 4. In polarographic analysis a two electron reduction to Br2CN02 and Br is indicated (Ref 5). It adds to olefins to form 1,1,1-tribromo-2-nitroalkanes, The authors found that it is the only halonitroalkane to react in this way (Ref 3). When added to liq ammonia it forms a mixt of the Amm salt of dibromonitromethane and Amm bromide (see above) (Ref 2)... 

See other catalytic nitro reduction processes, hydrogenation incidents See related nitroalkanes... 

The reduction of nitroalkenes with ZnBH4 in 1,2-dimethoxyethane (DME) gives the corresponding oximes or nitroalkanes depending on the structure of nitroalkenes. a-Substituted nitroalkenes are reduced to the oximes, whereas those having no a-substituents afford the... 

Very selective reduction of nitroalkenes into the corresponding nitroalkanes is achieved using NaCNBH3 in the presence of the zeolite H-ZSM 5 in methanol (Eq. 3.48).78... 

Nitromethylation of aldehydes has been carried out in a one pot procedure consisting of the Henry reaction, acetylation, and reduction with sodium borohydride, which provides a good method for the preparation of l-nitroalkanes.16b 79 It has been improved by several modifications. The initial condensation reaction is accelerated by use of KF and 18-crown-6 in isopropanol. Acetylation is effected with acetic anhydride at 25 °C and 4-dimethylaminopyridine (DMAP) as a catalyst. These mild conditions are compatible with various functional groups which are often... 

Reduction of 1-nitro-1-alkenes with fermenting Baker s yeast proceeds enantioselectively to give optically active nitroalkanes (Eq. 3.53).81... 

The Michael addition of nitro compounds is a useful method for the preparation of various natural products. The Michael addition of nitroalkanes to dehydroalanines gives y-nitro-a-amino acids, which provides a convenient synthesis of side-chain modified a-amino acids (Eq. 4.114).152 Transformations of y-nitro-a-amino acid derivatives into a-amino acids occur by reductive denitration (see Section 7.2) into y-oxygenated a-amino acids by the Nef reaction (Eq. 

Ballini and coworkers have developed a new strategy for alkenylation of carbonyl compounds based on the Michael addition followed by elimination of HN02 (see Section 7.3). A variety of 2-alkylidene 1,4-dioles have been conveniently prepared, in two steps, by the Michael addition of a nitroalkane to the appropriate enedione derivatives under basic conditions, followed by chemoselective reduction with LiAlH4 (Eq. 4.123).170... 

Barton and coworkers have explored the arylation of various nucleophiles including nitroalkanes using bismuth reagents.105 Reaction of 2-nitropropane with triphenylbismuth carbonate gives 2-nitro-2-phenylpropane in 80% yield.106 Recently, this arylation has been used for the synthesis of unusual amino acids. Arylation of a-nitro esters with triphenylbismuth dichloride followed by reduction gives unique a-amino acids (Eq. 5.68).107... 

The conversion of primary or secondary nitro compounds into aldehydes or ketones is normally accomplished by use of the Nef reaction, which is one of the most important transformations of nitro compounds. Various methods have been introduced forthis transformation (1) treatment of nitronates with acid, (2) oxidation of nitronates, and (3) reduction of nitroalkenes. Although a comprehensive review is available,3 important procedures and improved methods published after this review are presented in this chapter. The Nef reaction after the nitro-aldol (Henry reaction), Michael addition, or Diels-Alder reaction using nitroalkanes or nitroalkenes has been used extensively in organic synthesis of various substrates, including complicated natural products. Some of them are presented in this chapter other examples are presented in the chapters discussing the Henry reaction (Chapter 3), Michael addition (Chapter 4), and Diels-Alder reaction (Chapter 8). 

The conversion of nitroalkanes to ketoximes can be achieved by the reduction with Zn in acetic acid,112 or Fe in acetic acid.113 Nitroalkenes are direcdy reduced into saturated ketoximes by these reagents, which are precursors for ketones (see Section 6.1.4 Nef reaction). Reduction of 3-O-ace-ty lated sugar 1 -nitro-1 -alkenes with Zn in acetic acid gives the corresponding 2,3-unsaturated sugar oximes in high yield, which is a versatile route to 2,3-unsaturated sugar derivatives (Eq. 6.58).114... 

Table 7.2. Bu3SnH-catalyzed reduction of nitroalkane to alkanes...

Alkenylation using nitroalkanes followed by the selective reduction of the double bonds with NiCl2 and NaBH4 can be regarded as the addition of alkyl anions to electron-deficient alkenes (Eq. 7.127).173... 

Very simple synthesis of a-substituted y-methyl-y-lactones is also possible by olefination using nitroalkanes followed by reduction, as shown in Eq. 7.128.174... 

The Michael addition of nitroalkanes to a, P-unsaturated ketones gives y-nitroketones, which are converted into pyrroles by reduction of the nitro group with Bu3P and PhSSPh (Eq. 10.2).4... 

The cycloaddition, reduction and oxidation reactions emanating from a,/J-unsatu-rated nitroalkenes provide easy access to a vast array of functionalities that include nitroalkanes, N-substituted hydroxylamines, amines, ketones, oximes, and a-substi-tuted oximes and ketones [73-75], Consequently, there are numerous possibilities of using these in situ generated nitroalkenes for the preparation of valuable building blocks and synthetic precursors. 

Supplemental Reference for Table 25. Organosilane Reduction of Nitroalkanes... 

Use of copper and silver salts in ethylenediamine solution provides a method for catalytic H2 reduction of nitroalkanes to oximes (541) ... 

Reduction of nitroalkanes RNO2 with samarium(II) iodide, obtained from samarium and 1,2-diiodoethane, yields either alkylhydroxylamines RNHOH or alkylamines RNH2, depending on the amount of the reagent434. The base-catalysed reaction of nitroalkanes with phenyl(vinyl) sulphoxide (399) yields the conjugate adducts 400, which fragment to allylic nitro compounds 401 on thermolysis435. 

Oximes RCH=NOH are produced in the reduction of nitroalkanes RCH2NO2 by carbon disulphide in the presence of triethylamine461 or wet potassium carbonate and... 

---