Reduction of nitroalkene

A new selective reduction of nitroalkenes into enamides has been carried out by a combina-m of iron powder, a carboxylic acid, and the corresponding anhydnde fEq 6 64)... 

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... 

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). 

Iodotrimethylsilane generated in situ from chlorotrimetylsilane and sodium iodide effects the reduction of nitroalkenes into ketones at 0 °C. This method is useful for the conversion of nitro steroids or nitro terpenoids to the corresponding ketones (Eq. 6.24).43... 

Reaction of the salts of primary and secondary alky Initio compounds with diborane in THF solution at 25 °C yields the corresponding hydroxylamines.117 Kabalka has reported the reduction of nitroalkenes to hydroxylamines or amines with a variety of borane and borohydride reagents (Eq. 6.61).118... 

In spite of the success of asymmetric iridium catalysts for the direct hydrogenation of alkenes, there has been very limited research into the use of alternative hydrogen donors. Carreira and coworkers have reported an enantioselective reduction of nitroalkenes in water using formic acid and the iridium aqua complex 69 [66]. For example, the reduction of nitroalkene 70 led to the formation of the product 71 in good yield and enantioselectivity (Scheme 17). The use of other aryl substrates afforded similar levels of enantioselectivity. 

Most of the current preparative methods of oximes from nitroalkenes are not versatile. Reduction of nitroalkenes by CrCl2 or NaH2P02 in the presence of palladium was reported to afford the corresponding oximes, but the yields are not satisfactory. Zn-acetic acid and Na2Sn02 reductions are limited to the preparation of ketoximes only. Electroreduction of alkenes was reported to yield mixmres of ketones and ketoximes, or oximes and acetals (or ketones) depending on the strucmre of nitroalkanes. 

A systematic study on enzymatic catalysis has revealed that isolated enzymes, from baker s yeast or old yellow enzyme (OYE) termed nitroalkene reductase, can efficiently catalyze the NADPH-linked reduction of nitroalkenes. Eor the OYE-catalyzed reduction of nitrocyclohexene, a catalytic mechanism was proposed in which the nitrocyclohexene is activated by nitro-oxygen hydrogen bonds to the enzymes His-191 and Asn-194 [167, 168]. Inspired by this study Schreiner et al. 

Erick Caireira of ETH Honggerbcrg has reported Organic Lett. 2004,6,4575) a catalytic procedure for the reduction of nitroalkenes such as 4 to the nitroalkane 5 with high enantiomeric excess. He has also reported (Angew. Chem. Int. Ed. 2005,44,612) that the enantiomerically-enriched nitroalkane can be converted to the corresponding nitrile 6 without loss of stereochemical purity. 

Reduction of nitroalkenes. a, p-Unsaturated nitro compounds can be reduced to hydroxylamines by BH3 THF in the presence of a catalytic amount of sodium borohydride (equation I).1... 

Reduction of nitroalkenes.3 1-Nitroalkenes are reduced in an alcohol medium by SnCl2-2H20 to a-alkoxy oximes in 70-90% yield. 

Reduction of nitroalkenes. Vinyl nitro compounds are reduced to saturated ketones or aldehydes by Raney nickel and an aqueous solution of sodium hypophosphite. Ester groups, C=C bonds, and aryl NO, and halo groups are not reduced. Under these conditions nitroalkanes arc reduced to amines, and oximes are converted into carbonyl compounds in high yield. 

Reduction of nitroalkenes Nitroalkenes substituted with at least one aryl group are reduced to alkenes rapidly at room temperature by reaction with NagS 9H2O and thiophenol in DMF. Thiophenol is essential as a proton source for this reduction it is converted into diphenyl disulfide during the reaction. 

The reduction of nitroalkanes to A -monosubstituted hydroxylamines has not been extensively explored. The classical approach involves electrolytic reduction of primary and secondary nitroalkanes. Catalytic hydrogenation and hydride reductions of nitroalkenes also yield hydroxylamine derivatives. 

Alkylamines are generally accessible via the reduction of nitroalkenes with lithium aluminum hy-dride. Substituted thienylethylamines can also be obtained using this methodology (equation 30). 

The reduction of nitroalkenes to ketones and oximes may be further illustrated by the following specific example ... 

Using the same reagent, the reduction of nitroalkenes to the corresponding nitroalkanes in methanol has been reported [107]. Again, filtration of the reaction... 

Tomioka, H., K. Ueda, H. Ohi, and Y. Izawa, Photochemical and Chemical Reduction of Nitroalkenes Using Viologens as an Electron Phase Transfer Catalyst, Chem Lea, 1359 (1986). 

The Nef reaction has also been used in the construction of the 7-deoxy-ABC ring taxane skeleton. As shown below, conjugate reduction of nitroalkene 41 with NaBFU followed by oxidation of the resulting nitronate salt with K2CO3/H2O2 provided tetracycle 42 in 60% yield.24 These reaction conditions are sufficiently mild to tolerate the presence of ketone and silyl ether functional groups in the molecule. 

Reduction of nitroalkenes. y-Acetoxy nitroalkenes are converted to unsaturated oximes, and the method is applicable to the synthesis of 2,3-unsaturated sugars. ... 

General procedure for the reduction of nitroalkenes using copper(II)-fluoride-derived CuH and nitromethan ... 

Hydroxylamines have been obtained from reductions of nitroalkenes with borane-tetrahydrofuran, and it has also been shown that catalytic quantities of sodium borohydride greatly accelerate the rates 454... 

Tomioka H, Ueda K, Ohi H, Izawa Y (1986) Photochemical and chemical reduction of nitroalkenes using viologens as an electron phase-transfer catalyst. Chem Lett 1359-1362... 

Kawai, Y, Inaba, Y, and Tokitoh, N. (2001) Asymmetric reduction of nitroalkenes with baker s yeast. Tetrahedron ... 

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