Nitroalkenes functionalized

Organometallics bearing esters (Eq. 4.102),13015 dienes (Eq. 4.103),131 or oxygen functions (Eq. 4.104)132 give nitroalkenes functionalized by these groups. 

The third cycloaddition substrate explored the feasibility of a vinyl nitro functionality as an activated dipolarophile (98, Scheme 1.9c). Preparation of nitroalkene oxidopyridinium betaine 98 began with silylenol ether 92, which was treated with methoxydioxolane in the presence of Lewis acid catalyst, TrC104, to afford keto dioxolane 93 in 58 % yield [47]. Ketone 93 then underwent a-nitration by treatment with /-BuONCL and KOt-Bu to provide nitro ketone 84 (91 %), which was then converted to the nitroalkene functionality via reduction under Luche conditions to... 

Under basic conditions, a-nitroalkenes function as synthetic equivalents of allylic nitro compounds 3-nitro-3-hexene, for instance, reacts with piperidine in the presence of Pd(PPh3)4, to give 2-piperidinyl-3-hexene (equation 139)459. 

The Michael adclidon of a nitrogen-centered nucleophile to nitroalkenes affords compounds that may serve as precursors of vicinal chamines, since the nitro group can be reduced to an amino function by reduction The very convenient method for the preparation of 1,2-chamines is developed by the adchdon of O-ethyihydroxylamines to nitroalkenes followed by redncdon with H-, in the presence of PckC fEq 4 24 ... 

Functionalized nitroalkenes are important chenophiles in the Diels-Alder ri example, fE -methyl fi-nitroactylate is an impottant reagent in organic synthesis The nitre group can be readily eliminated the Diels-Alder reaction of fi-nitroactylate is equivalent to that of ethyl propiolate with an inverse regiochemistry fEq. 8.4. ... 

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 Michael addition of allyl alcohols to nitroalkenes followed by intramolecular silyl nitronate olefin cycloaddition (Section 8.2) leads to functionalized tetrahydrofurans (Eq. 4.15).20... 

The addition-elimination reaction of hetero-atom-substituted nitroalkenes provides functionalized derivatives of unsaturated nitro compounds.26 Nitroenamines are generally prepared from a-nitro ketones and amines (see Chapter 5 regarding acylation of nitro compounds).26... 

Amino alcohols like (iS )-prolinol react with nitroalkenes very rapidly with very high facia] selectivity.31 Rapid and stereoselective reduction of the nitro function is essential for the conversion of the products to 1,2-diamine derivatives with the retention of the configuration. Samarium diiodide is recommended in the stereoselective reduction of thermally unstable 2-aminonitroalkanes to give a range of useful 1,2-diamines (Eq. 4.26).32... 

Reactions of zinc-copper reagents bearing acidic hydrogen and sulfur functionalities with various electrophiles, including nitroalkenes, have been reported, as shown in Eq. 4.86108 and Eq. 4.87,109 respectively. 

Interesting intramolecular cyclization of 1-nitroalkyl radicals generated by one-electron oxidation of aci-nitro anions with CAN is reported. As shown in Eq. 5.44, stereoselective formation of 3,4-functionalized tetrahydrofurans is observed.62 l-Nitro-6-heptenyl radicals generated by one electron oxidation of aci-nitroanions with CAN afford 2,3,4-trisubstituted tetrahydropyrans.63 The requisite nitro compounds are prepared by the Michael addition of 3-buten-l-al to nitroalkenes. 

The Nef reaction is accelerated by the presence of silicon atom at y-position of nitro functions, as shown in Eq. 6.3. The presence of the y-silicon is essential for such smooth reaction.6 The conversion of 5-nitrobicyclo[2.2.1]heptenes to the corresponding ketones via the Nef reaction is very complicated by the degradation of the product. Thus, (3-trimethylsilyl ketones can be prepared by a one-flask method via the addition of Grignard reagents containing trimethylsilyl groups to nitroalkenes and the subsequent hydrolysis, as shown in Eq. 6.4. 

The 4-hydroxyheptadecan-7-one, isolated from the root of Chiococca alba, is simply prepared using hydroxy-functionalized nitroalkenes, as shown in Eq. 6.29... 

The reaction of nitroalkenes or nitroalkanes with TiCl4 and Me3SiN3 gives a-azido functionalized hydroxamoyl chlorides, which act as precursors of nitrile oxides (Eq. 6.34).59... 

Furthermore, a neighboring group participation of a phenylthio function is observed in the Lewis acid-catalyzed nucleophilic substitution reaction of various P-nitrosulfides. Because the P-nitrosulfides are readily available, by the Michael addition of thiols to nitroalkenes (see Michael addition Chapter 4), this reaction is very useful. The P-nitrosulfides are prepared stereoselectively, and the reaction proceeds in a stereo-specific way (retention of configuration) as shown in Eqs. 31-34.35... 

Diels-Alder reactions are one of the most fundamental and useful reactions in synthetic organic chemistry. Various dienes and dienophiles have been employed for this useful reaction.1 Nitroalkenes take part in a host of Diels-Alder reactions in various ways, as outlined in Scheme 8.1. Various substituted nitroalkenes and dienes have been employed for this reaction without any substantial improvement in the original discovery of Alder and coworkers.2 Nitrodienes can also serve as 4ti-components for reverse electron demand in Diels-Alder reactions. Because the nitro group is converted into various functional groups, as discussed in Chapters 6 and 7, the Diels-Alder reaction of nitroalkenes has been frequently used in synthesis of complex natural products. Recently, Denmark and coworkers have developed [4+2] cycloaddition using nitroalkenes as heterodienes it provides an excellent method for the preparation of heterocyclic compounds, including pyrrolizidine alkaloids. This is discussed in Section 8.3. 

Michael additions of secondary allylamines to nitroalkenes followed by treatment with Me3SiCl and Et3N afford highly functionalized pyrrolidines via the stereoselective ISOC reaction (Eq. 8.86).137... 

Scheme 8.27 presents a highly stereoselective one-pot tandem 1,4-addition-ISOC for the construction of functionalized carbocycles. Addition of Grignard reagents to nitroalkenes and subsequent ISOC are carried out in one pot. The advantages of ISOC over INOC, namely, greater stereoselectivity and adaptability to one-pot conditions, have been demonstrated in Scheme 8.27.138... 

One-pot tandem reactions, starting with nitroalkenes and allyl alcohols leading to functionalized tetrahydrofurans, have been reported (Eq. 8.87).139... 

Recently, Denmark and coworkers have developed a new strategy for the construction of complex molecules using tandem [4+2]/[3+2]cycloaddition of nitroalkenes.149 In the review by Denmark, the definition of tandem reaction is described and tandem cascade cycloadditions, tandem consecutive cycloadditions, and tandem sequential cycloadditions are also defined. The use of nitroalkenes as heterodienes leads to the development of a general, high-yielding, and stereoselective method for the synthesis of cyclic nitronates (see Section 5.2). These dipoles undergo 1,3-dipolar cycloadditions. However, synthetic applications of this process are rare in contrast to the functionally equivalent cycloadditions of nitrile oxides. This is due to the lack of general methods for the preparation of nitronates and their instability. Thus, as illustrated in Scheme 8.29, the potential for a tandem process is formulated in the combination of [4+2] cycloaddition of a donor dienophile with [3+2]cycload-... 

When l-alkoxy-l,4-pentadienes are used instead of 2-alkoxy-l,4-pentadienes, tandem inter [4+2]/intra [3+2] cycloaddition of nitroalkenes followed by hydrogenolysis affords a versatile asymmetric synthesis of highly functionalized aminocyclopentanes (Scheme 8.47).186... 

Another pyrrole synthesis based on intramolecular substitution of the nitro group by amino function is presented in Eq. 10.7, in which the Michael addition of enamines to nitroalkenes is used.9... 

Clearly, the nitroalkene dipolarophile oxidoisoquinolinium betaine 123 is nonideal for the synthesis of the hetisine alkaloids, as mass throughput for the needed cycloadduct would be low, and conversion of the tertiary nitro group to carbon-based functionality, as would be required in the latter stages of the synthesis, could be problematic. On the other hand, an ene-nitrile dipolarophile has several potential advantages over nitroalkene dipolarophile. Most importantly, the ene-nitrile cycloadduct has carbon functionality installed at the C-10 position. Second, the conjugate addition byproduct pathway that occurs so readily for the nitroalkene oxidoisoquinolinium betaine 123 system (see Scheme 1.13) should be much slower... 

The cycloaddition, reduction and oxidation reactions emanating from a,/J-unsatu-rated nitroalkenes provide easy access to a vast array of functionalities that include nitroalkanes, N-substituted hydroxylamines, amines, ketones, oximes, and a-substi-tuted oximes and ketones [73-75], Consequently, there are numerous possibilities of using these in situ generated nitroalkenes for the preparation of valuable building blocks and synthetic precursors. 

Mobashery and co-workers also reported the synthesis and inhibitory apph-cation of 2 -N02 derivatives of neamine and kanamycin (Scheme 4.28). Using the metal-chelating method, the 2 -NH2 was selectively unmasked and then oxidized into 2 -N02, which will increase the acidity of 2 -H. Upon phosphorylation at the 3 -0H, elimination of phosphate will lead to the formation of a nitroalkene intermediate, 198, that can function as a Michael acceptor and... 

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