JS-nitrostyrenes

Although the enamine (30) underwent addition reaction with ethyl azido-dicarboxylate, it failed to add another mole of jS-nitrostyrene. In a similar manner the morpholine enamine of 2-methylcyclohexanone also failed to react with this olefin, i.e., jS-nitrostyrene, which is undoubtedly due to the 1,3-diaxial interaction between the methyl group and the incoming electrophile in the transition state. 

Similarly, jS-nitrostyrene (60) reacted with 1-dimethylamino-l-alkylbuta-dienes to afford phenylnitrocyclohexenes [55] (Equation 2.21) regioselectively and stereoselectively. 

The versatility of the INOC reaction is evident from the synthesis of tetrahy-drofurans fused to an isoxazoline 22a-f (Eq. 3) [181. a-Allyloxyaldoximes 21, formed by the reduction of jS-nitrostyrenes 19 with SnCl2 2H2O in the presence of an unsaturated alcohol 20, are transformed to isoxazolines 22 in high yield on treatment with NaOCl via stereoselective ring closure of a nitrile oxide intermediate (Table 2). 

These reactions are stereospecific in that the phenyl and nitrogroups derived from the jS-nitrostyrene are always trans. In the addition of 1,1-diphenyl-ethylene, the phenyl groups are situated on adjacent carbon atoms in the product (43). Only one isomer is thus formed. Stereospecificity in this reaction is postulated to arise as follows ... 

The addition of substituted anilines to frani -jS-nitrostyrene has been reported to involve the formation of a zwitterionic intermediate in the rate-determining step, followed by a rapid intramolecular proton transfer. " ... 

In the NMR spectra of benzene derivatives, apart from the Jen, only the meta coupling Jqh, but not Jqh) is resolved. A benzenoid CH, from whose perspective the meta positions are substituted, usually appears as a Jqh doublet without additional splitting, e.g. in the case of 3,4-dimethoxy-jS-methyl-jS-nitrostyrene (9) (Fig. 2.9) the carbon atom C-5 generates a doublet at 111.5 ppm in contrast to C-2 at 113.5 ppm which additionally splits into a triplet. The use of the CH coupling constant as a criterion for assigning a resonance to a specific position is illustrated by this example. 

Similar results were found with 1 -nitropropene (Eq. [2] and vide supra) (14). The addition process again provided only one detectable diastereomer, which was assigned syn configuration by analogy to the results with jS-nitrostyrenes. Piperidine and pyrrolidine enamines gave similar results, although the corresponding intermediate enamine adducts could not be isolated. 

Ar—C=C—N< (jS-nitrostyrenes,83 1-methylindoles84) however, bicyclic nitroalkenes are smoothly converted into the saturated amines by lithium aluminum hydride85 although their reduction by Raney nickel is incomplete salo, / -unsaturated cyanoacetic esters86 and occasional vinyl ketones87 can be reduced in good yield. 

Cycloaddition of (345) and ( )-jS-nitrostyrene gives stereospecifically the rranj-adducts <85TL5119>. The lower stereospecificity observed <79JPR(32l)555> was explained as epimerization catalyzed by silica gel and small amounts of pyrazolidinone <85TL5123>. Benzyne, generated by thermal decomposition of benzenediazonium-2-carboxylate, can also be used as 1,3-dipolarophile in the reaction with azomethine ylides (Scheme 70) <91T9599>. 

Based on relative reactivities towards diarylchloroethylenes and jS-bromo-p-nitrostyrenes. 

The reactivity of the halide ions could not be evaluated directly since they have not been studied with the same substrate. However, jj-toluene-thiolate ion is nine orders of magnitude more reactive than chloride ion towards 2-chloro-l,l-diarylethylenes in dimethylformamide. Although comparison may not be justified (see below), a similar reactivity ratio exists for the reactions of ]3-bromo-j)-nitrostyrene with iodide ion in butyl cellosolve and thiophenoxide ion in methanol. Bromide ion is 0-6 times as reactive as chloride ion towards l-anisyl-l-phenyl-2-chloroethylene. These relative reactivities of the halide ions should be regarded only as rough estimates. Their very low reactivity is also shown by the chloride exchange in ethyl jS-ohlorocrotonate, which is at least 10 times slower than the substitution by thioethoxide ion (Jones et al., 1960) while trichloroethylene does not exchange at all even at 245° (Bantysh et al., 1962). 

The Michael adducts of jS-ketoesters and -nitrostyrenes can be reduced to 4-arylpyrrole-3-carboxylate esters (Scheme 6) <85LA239>. It has been suggested that cyclization may occur at the oxime reduction level. 

The substrate used for assay purposes was diethyl maleate. Among the most active substrates were w-nitrostyrene and 3,4-dimethoxy- J-sty ene, ethylvinyl ketone, hexene-l-ai, and cycIohex-2-ene-l-one. The enzjTne is closely associated with the other glutathione transferases in rat liver preparations. When a rat liver supernatant was dialyzed, 50% of the activities of glutathione S-alkyitransferase and iS poxidetransferase were lost but over 80% of the jS-alkenetransferase was retained. The enzyme has not been obtained free of substantial amounts of the jS-aryltransferase. 

---