Nitro compounds reactions with alkenes

Primary nitro compounds are good precursors for preparing nitriles and nitrile oxides (Eq. 6.31). The conversion of nitro compounds into nitrile oxides affords an important tool for the synthesis of complex natural products. Nitrile oxides are reactive 1,3-dipoles that form isoxazolines or isoxazoles by the reaction with alkenes or alky nes, respectively. The products are also important precursors for various substrates such as P-amino alcohols, P-hydroxy ketones, P-hydroxy nitriles, and P-hydroxy acids (Scheme 6.3). Many good reviews concerning nitrile oxides in organic synthesis exist some of them are listed here.50-56 Applications of organic synthesis using nitrile oxides are discussed in Section 8.2.2. 

Explosive reaction with alkenes + diiodomethane, sulfur dioxide. Reacts violently with bromine, water, nitro compounds. Ignites on contact with air, ozone, methanol, or hydrazine. Reacts violently with nonmetal halides (e.g., arsenic trichloride or phosphorus trichloride) to produce pyrophoric triethyl arsine or triethyl phosphine. To fight fire, do not use water, foam, or halogenated extinguishing agents. Use dty materials, such as graphite, sand, etc. When heated to decomposition it emits toxic fumes of ZnO. See also ZINC COMPOUNDS. 

N-oxides or nitro compounds. These groups figure prominently in many synthetic transformations. In section 2.9.C, N-oxides, sulfoxides and selenoxides were important intermediates for syn-elimination reactions. In this chapter (sec. 3.5.B), N-oxides were used to catalyze osmylation reactions with alkenes. In sections 8.6 and 8.8.B, sulfoxides and sulfones will be used to stabilize carbanions, which react to form carbon-carbon bonds. It is therefore fitting that this chapter conclude with a brief survey of the methods for oxidizing these important synthetic intermediates. 

Catalytic hydrogenation is commonly used for the reduction of alkenes, alkynes, aromatic hydrocarbons, and aromatic heterocycles, carbonyl derivatives, nitriles, and nitro compounds. The reaction with alkenes proceeds on the surface of a heterogeneous metal catalyst, via cleavage of diatomic hydrogen and adsorption... 

Nitroso compounds and their reaction with alkenes have been very well characterized. Reactions of aryl or acyl nitroso compounds have demonstrated synthetic utility. Interestingly, reaction of aryl nitroso compounds did not display analogous selectivity to TAD nor 02 but instead displayed a selectivity of its own. Reaction of / -nitro-nitrosobenzene manifested a selectivity for abstraction from the twix group (see 88). An example of this was the conversion of 98 into 100, the only compound reported to form. ... 

The two major methods of preparation are the cycloaddition of nitrile oxides to alkenes and the reaction of a,/3-unsaturated ketones with hydroxylamines. Additional methods include reaction of /3-haloketones and hydroxylamine, the reaction of ylides with nitrile oxides by activation of alkyl nitro compounds from isoxazoline AT-oxides (methoxides, etc.) and miscellaneous syntheses (62HC(i7)i). 

The reaction of alkyl nitro compounds with acetyl chloride in the presence of an alkenic compound produced a 2-isoxazoline. The mechanism is believed to proceed via a nitrile oxide and is illustrated in Scheme 112 (B-79MI41613). 

Nitro compounds have been converted into various cyclic compounds via cycloaddition reactions. In particular, nitroalkenes have proved to be useful in Diels-Alder reactions. Under thermal conditions, they behave as electron-deficient alkenes and react with dienes to yield 3-nitrocy-clohexenes. Nitroalkenes can also act as heterodienes and react with olefins in the presence of Lewis acids to yield cyclic alkyl nitronates, which undergo [3+2] cycloaddition. Nitro compounds are precursors for nitrile oxides, alkyl nitronates, and trialkylsilyl nitronates, which undergo [3+2]cycloaddition reactions. Thus, nitro compounds play important roles in the chemistry of cycloaddition reactions. In this chapter, recent developments of cycloaddition chemistry of nitro compounds and their derivatives are summarized. 

As discussed in Section 6.2, nitro compounds are good precursors of nitrile oxides, which are important dipoles in cycloadditions. The 1,3-dipolar cycloaddition of nitrile oxides with alkenes or alkynes provides a straightforward access to 2-isoxazolines or isoxazoles, respectively. A number of ring-cleaving procedures are applicable, such that various types of compounds may be obtained from the primary adducts (Scheme 8.18). There are many reports on synthetic applications of this reaction. The methods for generation of nitrile oxides and their reactions are discussed in Section 6.2. Recent synthetic applications and asymmetric synthesis using 1,3-dipolar cycloaddition of nitrile oxides are summarized in this section. 

Nitroalkanes react with Jt-deficient alkenes, for example, p-nitro ketones are produced from a,P-unsaturated ketones [41], whereas allylic nitro compounds have been prepared via the Michael-type addition of nitroalkanes with electron-deficient alkynes (Table 6.19). The reaction in either dimethylsulphoxide [42] or dimethyl-formamide [43] is catalysed by potassium fluoride in the presence of benzyltriethyl-ammonium chloride the reaction with dimethyl acetylenedicarboxylate is only successful in dimethylsulphoxide [42], Primary nitroalkanes produce double Michael adducts [42,44], A-Protected a-aminoacetonitriles react with alkynes under catalysed solidiliquid conditions to produce the Michael adducts [45] which, upon treatment with aqueous copper(Il) sulphate, are converted into a,p-unsaturated ketones. 

Alkenes react with dinitrogen pentoxide in chlorinated solvents to give a mixture of /3-nitro-nitrate, vic-dinitro, vic-dinitrate ester and nitroalkene compounds. At temperatures between -30 °C and -10 °C the /3-nitro-nitrate is often the main product. The /3-nitro-nitrates are inherently unstable and readily form the corresponding nitroalkenes." Propylene reacts with dinitrogen pentoxide in methylene chloride between -10 °C and 0°C to form a mixture of l-nitro-2-propanol nitrate (27 %) and isomeric nitropropenes (12 %). The same reaction with cyclohexene is more complicated." ... 

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