Nitration of alkenes

There are many reports for nitration of alkenes using various nitrating agents, which proceeds via an ionic or radical addition process.49 Nitration of cyclohexene with acetyl nitrate gives a mixture of 3-and y-nitrocyclohexenes, 1,2-nitroacetate, and 1,2-nitronitrate. This reaction is not a simple ionic or radical process instead, [2+2] cycloaddition of nitryl cation is proposed.50... 

The synthetic applications of this reagent to the synthesis of nitroalkenes have been known since the 1960s.60 Nitration of alkenes with nitryl iodide, generated in situ from iodine and silver nitrite, is convenient for the synthesis of P-nitrostyrenes with various functional groups.61 This method is applied to the synthesis of ortho-methoxylated phenylisopropylamines, which are potent serotonine agonists (Eq. 2.31).62... 

The synthesis of cyclic nitroalkenes via nitration of cycloalkenes is summarized in Table 2.2. Acyclic nitroalkenes are more readily prepared via the Henry reaction than by nitration of alkenes (see Section 3.2.1). 

Because nitration of alkenes with nitronium salts proceeds via carbocation intermediates, nitration of electron-deficient alkenes with nitronium salts is rare. Only a few cases are reported. The reaction of a,(3-unsaturated esters with nitronium salts affords products via highly reactive ot-carbonyl cations.75... 

Allyl acetates are more commonly used as electrophiles for the palladium-catalyzed allylic alkylation than allylic nitro compounds.20 However, the reaction of allylic nitro compounds has found wider applications. Allylic nitro compounds are readily available by nitration of alkenes. The regio- and stereoselective introduction of electrophiles and nucleophiles into alkenes is possible as outlined in Eq. 7.19. In fact, this strategy is applied to the synthesis of terpenoids.21... 

NITRATION OF ALKENES AND ALKYNES WITH CONCENTRATED NITRIC ACID... 

Nitration of alkenes and allcynes with concentrated nitric acid... 

Nitrations. Nitration of alkenes performed with NO in 1,2-dichloroethane a are dehydrated by heating with acidic alum Anisole and its derivatives are nitrated u Reductive deamination Aromauc compounds with NO in THF under argon 1... 

Nitrations Nitration of alkenes (e.g., styrene to P-nitrostyrene) is readily performed with NO in 1,2-dichloroethane at room temperature. Nitro alcohol side products are dehydrated by heating with acidic alumina. 

Extensive studies of the NO2BF4 nitration of alkenes were reported in the Soviet literature and an excellent review has appeared [86]. 

Andrews MA, Chang TCT, Cheng CWF, Kapustay LV, Kelly KP, Zweifel MJ (1984) Nitration of alkenes by palladium nitro complexes. Organometallics 3 1479-1484... 

Mechanistically, the reactions of adamantane and ethers with NO are rationally explained by considering the formation of carbocations as transient intermediates (Scheme 6.14). The generation of PINO from NHPI in the presence of NO is confirmed by ESR measurements [170], but the formation of PINO by this method may be due to traces of NO2 contained in the reaction system. On the other hand, Suzuki has suggested the formation of a cationic species via a diazonium nitrate in the nitration of alkenes with N O [ 17 5 ]. The nucleophilic attack of the benzonitrile and water on the adamantyl and benzylic cations would result in the amide and aldehyde, respectively [170]. 

Nitration of Alkenes. Alkenes may also be nitrated by nitric acid. This reaction has been exploited in tbe synthesis of a number of steroid derivatives. Fuming nitric acid converts cholesteryl acetate to 6-nitrocbolesteryl acetate in good yield (eq 5). The nitration of the more highly functionalized dienyl acetate (eq 6) provides the corresponding nitro steroid. Treatment of 1,1-dichloro-2-fluoroethylene with nitric acid in concentrated sulfuric acid provides fluoronitroacetyl chloride in 16% yield. 2-Sulfolenes have also been nitrated. ... 

The authors of this work were concerned chiefly with additions to alkenes, and evidence about the mechanism of aromatic nitration arises by analogy. Certain aspects of their work have been repeated to investigate whether the nitration of aromatic compounds shows the same phenomena ( 5-3-6). It was shown that solutions of acetyl nitrate in acetic anhydride were more powerful nitrating media for anisole and biphenyl than the corresponding solutions of nitric acid in which acetyl nitrate had not been formed furthermore, it appeared that the formation of acetyl nitrate was faster when 95-98% nitric acid was used than when 70 % nitric acid was used. 

Because of Us high polarity and low nucleophilicity, a trifluoroacetic acid medium is usually used for the investigation of such carbocationic processes as solvolysis, protonation of alkenes, skeletal rearrangements, and hydride shifts [22-24] It also has been used for several synthetically useful reachons, such as electrophilic aromatic substitution [25], reductions [26, 27], and oxidations [28] Trifluoroacetic acid is a good medium for the nitration of aromatic compounds Nitration of benzene or toluene with sodium nitrate in trifluoroacetic acid is almost quantitative after 4 h at room temperature [25] Under these conditions, toluene gives the usual mixture of mononitrotoluenes in an o m p ratio of 61 6 2 6 35 8 A trifluoroacetic acid medium can be used for the reduction of acids, ketones, and alcohols with sodium borohydnde [26] or triethylsilane [27] Diary Iketones are smoothly reduced by sodium borohydnde in trifluoroacetic acid to diarylmethanes (equation 13)... 

Bordwell and Garbisch71 contested this conclusion since they found that nitric acid in acetic anhydride prepared at —10 °C contained a much less effective nitrating species (the nitric acid could be recovered quantitatively) than when mixed at 25 °C and cooled to —10 °C (the nitric acid being then mostly unrecoverable). Further, these latter solutions reacted with alkenes to give predominantly cis addition products (nitro-acetates), whi h indicates association of the nitronium ion with some other species. It has been argued72 that this does not necessarily follow, since nitration of aromatics may involve a different... 

A very attractive method for the preparation of nitroalkenes, which is based on the reaction with NO, has been reported. Treatment of alkenes at ambient pressure of nitrogen monoxide (NO) at room temperature gives the corresponding nitroalkenes in fairly good yields along with P-nitroalcohols in a ratio of about 8 to 2. The nitroalcohol by-products are converted into the desired nitroalkenes by dehydration with acidic alumina in high total yield. This simple and convenient nitration procedure is applied successfully to the preparation of nitroalkenes derived from various terminal alkenes or styrenes (Eq. 2.27).53 This process is modified by the use of HY-zeolites instead of alumina. The lack of corrosiveness and the ability to regenerate and reuse the catalyst make this an attractive system (Eq. 2.28).54... 

The well-known method of furazan formation is based on nitrosation of alkenes. Thus, several NO donor 3,4-disubstituted 1,2,5-oxadiazole 2-oxide derivatives and the related 1,2,5-oxadiazoles, containing methylsulfonylphe-nyl, phenylsulfonyl, sulfonylamidophenyl, and phenylsulfonylamido groups were synthesized by nitration of... 

Ammonium cerium(IV) nitrate on reaction with acetone or acetophenone generates acetyl- or benzoylformonitrile oxides, respectively (99). These nitrile oxides dimerize to furoxans and give, in the presence of alkenes and alkynes, 3-acetyl- or 3-benzoyl-4,5-dihydroisoxazoles and 3-acetyl- or 3-benzoylisoxazoles, respectively the yield of the isoxazole derivatives was improved on using ammonium cerium(III) nitrate tetrahydrate-formic acid (99). 

Stationary phases can be made highly selective by adding compounds to them which have affinities for certain chemical species. For example, silver nitrate, incorporated into a polar liquid preferentially retards the elution of alkenes by formation of weak -complexes. A selection of stationary phases with their maximum operating temperatures and useful applications is given in Table 4.10. 

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. 

---