Unsaturated nitroalkenes

Formic acid is a good reducing agent in the presence of Pd on carbon as a catalyst. Aromatic nitro compounds are reduced to aniline with formic acid[100]. Selective reduction of one nitro group in 2,4-dinitrotoluene (112) with triethylammonium formate is possible[101]. o-Nitroacetophenone (113) is first reduced to o-aminoacetophenone, then to o-ethylaniline when an excess of formate is used[102]. Ammonium and potassium formate are also used for the reduction of aliphatic and aromatic nitro compounds. Pd on carbon is a good catalyst[103,104]. NaBH4 is also used for the Pd-catalyzed reduction of nitro compounds 105]. However, the ,/)-unsaturated nitroalkene 114 is partially reduced to the oxime 115 with ammonium formate[106]... 

Exposure of mixtures of alkenes, ceric ammonium nitrate, acetic acid and chloroform to ultrasound leads to a,/i-unsaturated nitroalkenes. A free-radical mechanism was proposed for this reaction (equation 126)410. 

Scheme 6.25 Product range of the biomimetic reduction of a.P-unsaturated nitroalkenes catalyzed by 9 in the presence of 19.

Considering that a,P-unsaturated nitroalkenes are easily available starting material, it has been reported as a unique methodology for the efficient synthesis of both 3-nitro-l,2-dihydroquinolines and 3-nitrochromenes through nitroalkenes. 

Reduction of a, -unsaturated nitroalkenes. These nitroalkenes are reduced by BHj-THF and a catalytic amount of NaBH4 to alkylanines in 85-91% yield. 

Carbamoyl nitroso dienophiles, derived from chiral pyrrolidines, have been generated and their reactivity with cyclohexa-diene investigated. Using (—)-fra/w-2,5-dimethylpyirolidine as the auxiliary, the [4 + 2] cycloadduct is isolated in 82% yield and with 98% diastereomeric excess (eq 10). Similarly, chiral ynamine dienophiles have been utilized in asymmetric [4 + 2] cycloadditions with a,p-unsaturated nitroalkenes to afford cyclic nitronic esters. The resulting esters subsequently undergo a rapid [1,31-rearrangement to afford chiral cyclic nitrones in moderate yield and high diastereoselectivity (eq 11)-... 

The reduction of a,p unsaturated nitroalkenes provides a simple access to a vast array of functionalities, including amines. Early studies focused on the catalytic hydrogenation of the nitropropene derivative (52) 1 -(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (53) is obtained as a minor product in a... 

Nitroalkanes and a6-unsaturated nitroalkenes are known to undergo photorearrangements which yield the corresponding... 

Reductions. Disulfides are cleaved, and nitroaryl azides are reduced to the amines without affecting the nitro group or other substituents. However, p.y-unsaturated nitroalkenes are reduced to enones, and m-nitrostyrenes give a-allyloxy arylacetaldoximes in the presence of allyl alcohol. ... 

Modification of the strategy provides several routes to oxime ethers.465 Various a,8-unsaturated nitroalkenes were readily reduced to the corresponding oximes by sodium hypophosphite in the... 

The cycloaddition, reduction, and oxidation reactions of a,/i-unsaturated nitroalkenes provide easy access to a vast array of functionality that includes nitroalkanes, N-substituted hydroxylamines, amines, ketones, oximes, and a-substituted oximes and ketones [82-84]. Consequently, there are numerous possibilities of using these in situ generated nitroalkenes for preparation of valuable building blocks and synthetic precursors. 

An alternative synthetic route to (bicyclic) pyrroles 41 involves the coupling of a cyclic ketone with an amine and an a,/i-unsaturated nitroalkene on the surface of alumina (Scheme 17.30) [14]. After MW irradiation for 13-15 min the product 41 was obtained in 71-86% yield. In this synthesis, substitution on the a-position of... 

Bp3-OEt2 followed hy DiisobutyUduminum Hydride is used for the 1,2-reduction of y-aimno-Q, -unsaturated esters to give unsaturated amino alcohols, which are chiral building blocks for a -amino acids. Q , -Unsaturated nitroalkenes can be reduced to hydroxylamines by Sodium Borohydride and BF3-OEt2 in THF extended reaction times result in the reduction of the hydroxylamines to alkylamines. Diphenylamine-borane is prepared from sodium borohydride, BF3-OEt2, and diphenylamine in THF at 0 °C. This solid is more stable in air than BF3-THF and is almost as reactive in the reduction of aldehydes, ketones, carboxyhc acids, esters, and anhydrides, as well as in the hydrob-oration of alkenes. 

Oxa- and aza-Michael additions followed by intramolecular cyclizations occur when propargyl alcohols are treated with a, -unsaturated nitroalkenes in the presence of t-BuOK in THF. Although exo-3-methylene tetrahydrofurans are usually the major products of these reactions, 3,4-dihydropyrans are also obtained in some cases, depending upon the substituents present within the donor and acceptor. Equation 59 shows the results of the reactions of propargyl alcohol with four nitroalkenes. Similar reactions of methyl propargylamine with these same acceptors give exclusively 3-methylenepyrrolidines."... 

The oxidation, reduction and cycloaddition reactions originating from a,P-unsaturated nitroalkenes provide easy access to an array of functioruilities that... 

Novel a-hydrazino-a,p-unsaturated nitroalkenes 111, which exhibit dynamic phenomenon on the NMR time scale, have been synthesized in excellent yields via the imidazole or DMAP mediated aza-MBH reaction of nitroalkenes with azodicarboxylates (Scheme 2.49). ... 

Toogood, H.S., Fryszkowska, A., Hare, V., Fisher, K., Roujeinikova, A., Leys, D., Gardiner, J.M., Stephens, G.M., and Scrutton, N.S. (2008) Structure-based insight into the asymmetric bioreduction of the C=C double bond of a, 3-unsaturated nitroalkenes by pentaerythritol tetranitrate reductase. Adv. Synth, bated., 350, 2789-2803. 

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