Nitroalkane complexes

Synthesis of oximes and amines. Copper salts solubilized in aqueous alkyl polyamines solvents have been found to promote the homogeneous reduction of nitroalkanes to oximes by CO at atmospheric pressure and 85 C in good yields and conversion(9. Catalysis is favoured by the use of copper salts of weak acids solubilized in alkylpolyamlnes solvents of pKa > 9.2. The suggested reaction path involves the formation of a solvated cuprous carbonyl complex, which by combination with the nitroalkane anion gives a copper-nitroalkane complex ... 

Similarly, the reaction of nitroalkanes at 25 °C in the presence of three equiv. K2C03 selectively gives the monosubstituted complexes. [FeCpC6H4(Cl)CHRN02]+ (R = Me 74% Et 65% [101], Scheme XVIII). 

Jorgensen et al. [84] studied how solvent effects could influence the course of Diels-Alder reactions catalyzed by copper(II)-bisoxazoline. They assumed that the use of polar solvents (generally nitroalkanes) improved the activity and selectivity of the cationic copper-Lewis acid used in the hetero Diels-Alder reaction of alkylglyoxylates with dienes (Scheme 31, reaction 1). The explanation, close to that given by Evans regarding the crucial role of the counterion, is a stabilization of the dissociated ion, leading to a more defined complex conformation. They also used this reaction for the synthesis of a precursor for highly valuable sesquiterpene lactones with an enantiomeric excess superior to 99%. 

Anhydrous peroxytrifluoroacetic acid is not easy to handle, but the procedure has recently been revised.121 Namely, reaction of urea-hydrogen peroxide complex (UHP) with tri-fluoroacetic anhydride in acetonitrile at 0 °C gives solutions of peroxytrifluoroacetic acid, which oxidize aldoximes to nitroalkanes in good yields (Eqs. 2.58 and 2.59). Ketoximes fail to react under these conditions, the parent ketone being recovered. 

The conversion of oximes to nitroalkanes has been achieved by employing an Mo(IV) oxodiperoxo complex as oxidant in acetonitrile. Both aldoximes and ketoximes are converted into the corresponding nitroalkanes (Eqs. 2.61 and 2.62),123 representing a complementary synthetic route to the use of the UHP method. 

Monoanions derived from nitroalkanes are more prone to alkylate on oxygen rather than on carbon in reactions with alkyl halides, as discussed in Section 5.1. Methods to circumvent O-alkylation of nitro compounds are presented in Sections 5.1 and 5.4, in which alkylation of the a.a-dianions of primary nitro compounds and radial reactions are described. Palladium-catalyzed alkylation of nitro compounds offers another useful method for C-alkylation of nitro compounds. Tsuj i and Trost have developed the carbon-carbon bond forming reactions using 7t-allyl Pd complexes. Various nucleophiles such as the anions derived from diethyl malonate or ethyl acetoacetate are employed for this transformation, as shown in Scheme 5.7. This process is now one of the most important tools for synthesis of complex compounds.6811-1 Nitro compounds can participate in palladium-catalyzed alkylation, both as alkylating agents (see Section 7.1.2) and nucleophiles. This section summarizes the C-alkylation of nitro compounds using transition metals. 

Asymmetric synthesis of tricyclic nitro ergoline synthon (up to 70% ee) is accomplished by intramolecular cyclization of nitro compound Pd(0)-catalyzed complexes with classical C2 symmetry diphosphanes.94 Palladium complexes of 4,5-dihydrooxazoles are better chiral ligands to promote asymmetric allylic alkylation than classical catalysts. For example, allylic substitution with nitromethane gives enantioselectivity exceeding 99% ee (Eq. 5.62).95 Phosphi-noxazolines can induce very high enatioselectivity in other transition metal-catalyzed reactions.96 Diastereo- and enantioselective allylation of substituted nitroalkanes has also been reported.9513... 

The a-arylation of carbonyl compounds (sometimes in enantioselective version) such as ketones,107-115 amides,114 115 lactones,116 azlactones,117 malonates,118 piperidinones,119,120 cyanoesters,121,122 nitriles,125,124 sul-fones, trimethylsilyl enolates, nitroalkanes, esters, amino acids, or acids has been reported using palladium catalysis. The asymmetric vinylation of ketone enolates has been developed with palladium complexes bearing electron-rich chiral monodentate ligands.155... 

Aliphatic nitroalkanes can be categorized into six basic groups primary, secondary and tertiary nitroalkanes, terminal and internal gem-dinitroalkanes, and trinitromethyl compounds. Primary and secondary nitroalkanes, and terminal gem-dinitroalkanes, have acidic protons and find particular use in condensation reactions for the synthesis of more complex and... 

The nitration of moderate to high molecular weight alkane substrates results in very complex product mixtures. Consequently, these reactions are only of industrial importance if the mixture of nitroalkane products is separable by distillation. Polynitroalkanes can be observed from the nitration of moderate to high molecular weight alkane substrates with nitrogen dioxide. The nitration of aliphatic hydrocarbons has been the subject of several reviews. 

Some recent advances have been reported in oxime oxidation, including the in situ generation of peroxytrifluoroacetic acid from the reaction of urea hydrogen peroxide complex with TFAA in acetonitrile at 0 °C This method gives good yields of nitroalkanes from aldoximes but fails with ketoximes. 

Oxidative nitration, a process discovered by Kaplan and Shechter, is probably the most efficient and useful method available for the synthesis of em-dinitroaliphatic compounds from the corresponding nitroalkanes. The process, which is an electron-transfer substitution at saturated carbon, involves treatment of the nitronate salts of primary or secondary nitroalkanes with silver nitrate and an inorganic nitrite in neutral or alkali media. The reaction is believed ° °° to proceed through the addition complex (82) which collapses and leads to oxidative addition of nitrite anion to the nitronate and reduction of silver from Ag+ to Ag . Reactions proceed rapidly in homogeneous solution between 0 and 30 °C. 

In a collection of insightful pieces of work Enders has incorporated an iminium ion conjugate addition of nitroalkanes to a,P-unsaturated aldehydes into a triple cascade reaction generating up to four contiguous stereocentres in one pot, again indicative of the complexity attainable from superficially simple catalysts and techniques [175-177] (Scheme 46). 

The addition of Grignard reagents to nitroalkenes like 205 gives ad-salts 206, which can be further transformed into nitroalkanes, hydroxymoyl halides or carboxylic acids (equation 130) . Reaction of RMgX with nitroalkenes in the presence of CeCls, followed by treatment with 100% acetic acid, was developed as efficient synthesis of complex nitroalkanes . ... 

For synthesis of more complex target molecules by these strategies, nitroalkanes with additional O-functions are often required. Specifically, the above CC-forming additions lead to a variety of 1,3,4-, 1,3,5- and 1,3,6-functionalized structures, as shown with 3 (or nitropropyl ethers, from 2). 

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