Nitroethylene, reactions with

Unsaturated compounds activated by electron-attracting groups can also effect alkylation at the 3-position. An important example is the reaction with nitroethylene to form 3-(2-nitroethyl)indole [31731-23-4] (14). 

Sequential radical cyclizations are also featured in an efficient and clever synthesis of the cedrane framework 83 (see Scheme 15).30 Compound 81, the product of a regioselective Diels-Alder reaction between isoprene (79) and nitroethylene (80), participates in a nitroaldol reaction (Henry reaction) with 5-methyl-4-hexenal in the presence of a basic resin to give 82. Because the nitro group in... 

The Diels-Alder reaction of morphinan-6,8-dienes with nitroethene affords a novel type of opium alkaloids (Eq. 8.3).10a High reactivity of nitroethylene is demonstrated for the Diels-Alder reaction with thermally unstable dienes, and this is used for synthesis of polycyclic kopsane-like alkaloids.1013... 

Interestingly, bis(methylthio)-l-nitroethylene (380) reacts with dimetallic zinc-copper species leading to the corresponding exo-methylene cycloalkenes, such as 381 (Scheme 100) . / -Disubstitutcd nitroolefins are especially difficult to prepare by nitroaldol condensation. The addition of zinc-copper reagents to nitroolefins followed by a reaction with phenylselenyl bromide produces, after IFO, oxidation, EtZ mixtures of -disubstituted nitroalkenes, such as 382 (Scheme 100) . 

Thus, if you look at the different dienophiles in Fig. 2.1, the dimerization of butadiene 2.1 is slower than its reaction with acrolein 2.4. Methyl acrylate and methyl vinyl ketone have electron-withdrawing substituents Z of comparable power, and react at a similar rate, but cyclohexenone 2.5, which has a (5-alkyl substituent, is considerably less reactive. Nitroethylene has one of the most powerful electron-withdrawing groups, and is a very good... 

The reactivity and regioselectivity of 1-azidoadamantane (See Scheme 18), a bridgehead azide, have been investigated with electron-poor olefins.155 The reaction with ethyl acrylate proceeds smoothly at 25°C to afford exclusively the 4-substituted triazoline in good yield the regiochemistry is supported by 13C- and H-NMR spectral data. /S-Nitrostyrene and nitroethylene give only triazoles. 

Another strategy for the synthesis of lycorine commenced with the Diels-Alder reaction of l-methylenedioxyphenyl-2-nitroethylene with butadiene to provide the cyclohexene derivative 85, which on reaction with MCPBA gave 86 together with the diastereomeric epoxide (1 1) (Scheme 6) (112). Hydrogena-... 

As seen in the gitonic and vicinal systems, ammonium and related cationic centers may be components of superelectrophiles and reactive dications having the 1,3-dicationic structure. Several types of superelectrophilic aza-carbo dications have been studied in which protonated nitro groups are involved. For example, it was found that nitroethylene reacts with benzene in the presence of 10 equivalents of CF3SO3H to give deoxybenzoin oxime in 96% yield (eq 58).71 Since the reaction does not occur with only one equivalent of CF3SO3H, the formation of the /V./V -dihydroxy iminium-methyl dication 197 was proposed. In spectroscopic studies, the stable dication (199) can be directly observed by H and 13C NMR spectroscopy from solutions of l-nitro-2-methyl-l-propene (198) in CF3SO3H (eq 59). 

SMP is a useful chiral auxiliary in various cycloaddition reactions. Chiral 2-amino-1,3-dienes have been used in the Diels-Alder reaction with 2-aryl-1 -nitroethylenes, and 5-ary 1-2-methyl-substituted 4-nitrocyclohexanones were obtained in excellent enantiomeric purities (ee=95-99%) and diastereoselectiv-ities (ds = 75-95% eq 6). The photo-Diels-Alder reaction of SMP acrylonitrile with 1-acetylnaphthalene has been carried out. After hydrolysis of the adduct, the 1,4-diketone was obtained in excellent enantiomeric purity (ee > 97% eq 7). 

Because of its tendency to polymerize, nitroethylene is a somewhat challenging reactant. When the reaction with indole is conducted at room temperature the yield increases to 80% [266]. Recently, a comparison was done, using p-nitrostyrene, of the Mg salt, thermal and microwave irradiation. The microwave method was found most convenient. These conditions were also applicable to the a-methyl analog [267]. 

Without additional reagents Reactions with nitroethylene N- -Nitroethylation... 

Other methods of generating a-aminoketones in situ are common, if somewhat less general than the methods already described. 2-Nitrovinylpyrrolidine, which is readily available, yields 2,3-bis(3-aminopropyl)pyrazine on reduction and this almost certainly involves ring opening of the intermediate enamine to an a-aminoketone which then dimerizes under the reaction conditions (Scheme 59) (78TL2217). Nitroethylene derivatives have also served as a-aminoketone precursors via ammonolysis of the derived epoxides at elevated temperatures (Scheme 60) (76S53). Condensation of 1,1-disubstituted hydrazine derivatives with a-nitro-/3-ethoxyethylene derivatives has been used in the synthesis of l,4-dialkylamino-l,4-dihydropyrazines (Scheme 61) (77S136). 

Nitroisoxazoles have been synthesized by reaction of l-chloro-2-nitroethylene with nitrile N-oxides (75C350). 

Nitroolefins also offer the possibilities of 1,2 cycloaddition (37,57) or simple alkylation (57-59) products when they are allowed to react with enamines. The reaction of nitroethylene with the morpholine enamine of cyclohexanone led primarily to a cyclobutane adduct in nonpolar solvents and to a simple alkylated product in polar solvents (57). These products are evidently formed from kinetically controlled reactions since they cannot be converted to the other product under the conditions in which the other... 

Indole magnesium iodide reacts with nitroethylene to give 3-(2-nitroethyl)indole (351) in good yield (Noland and Hartman ). Noland et al. subsequently showed that this reaction, which is usually carried out in ether at 0°, was of general applicability and reported... 

The Michael type reaction of f3/f -5-r-butyldimethysiloxy-3-phenyl-l//-pyrrolo[l,2-c oxa2ole with nitroethylene proceeds in the presence of Lev/is acid to give the alkylated product in good chemical yield and diastereoselecdvity In the case of nitroethylene, the Diels-Alder type transition state is favored to give the ryu-adduct selectively fEq 4 72 ... 

Dehydration of P-nitro alcohols provides an important method for the preparation of nitroalkenes. Because lower nitroalkenes such as nitroethylene, 1-nitro-1-propene, and 2-nitro-l-propene tend to polymerize, they must be prepared carefully and used immediately after preparation. Dehydration with phthalic anhydride is the most reliable method for such lower nitroalkenes.42,43 Such lower nitroalkenes have been used as important reagents for Michael acceptors or dienophiles in the Diels-Alder reaction, which will be... 

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