Vinyl-nitro compound

Vinyl azides 50 (73CJC2406) and vicinal vinyl nitro compounds of type 51 (57JOC456, 75MI1) can be precursors for furoxans and furazans (Scheme 20). 

Tertiary nitroalkanes (R3C-N02) are neutral. The most important unsaturated analogues are the vinyl nitro compounds (e.g. R CH=CH-N02). All these nitro compounds have in recent years become of great interest as versatile intermediates in organic synthesis.196 Some of these aspects are noted in Chapter 1, p. 21, in Section 5.7.7, p. 599, and in Section 5.9.3, p. 635, and are further exemplified in the following discussion. 

Reduction of nitroalkenes. Vinyl nitro compounds are reduced to saturated ketones or aldehydes by Raney nickel and an aqueous solution of sodium hypophosphite. Ester groups, C=C bonds, and aryl NO, and halo groups are not reduced. Under these conditions nitroalkanes arc reduced to amines, and oximes are converted into carbonyl compounds in high yield. 

The reaction of vinyl nitro compounds (C=C-N02) and aryl iodide to give the styrene compound (C=C-Ar) was reported using BEt3 and exposure to arr. ... 

In a reaction termed a nitro-Hunsdiecker (see 14-30), vinyl carboxyhc acids (conjugated acids) are treated with nitric acid and a catalytic amount of AIBN (p. 935). The product is the vinyl nitro compound, generated via decarboxylation... 

The vinyl-nitro compound 200 serves as an excellent example to demonstrate the remarkable flexibihty and the very high synthetic potential for forming heterocyclic compounds in a highly predictable manner [73],... 

Substances that form carbanions, such as nitro compounds, hydrocyanic acid, malonic acid, or acetylacetone, react with vinyl ethers in the presence of water, replacing the alkyl group under mild conditions (245). 

Aromatic compounds (C5H5) Aromatic nitro compounds Aromatic alcohols Vinyl furans... 

Giomi s group developed a domino process for the synthesis of spiro tricyclic nitroso acetals using a, 3-unsaturated nitro compounds 4-163 and ethyl vinyl ether to give the nitrone 4-164, which underwent a second 1,3-dipolar cycloaddition with the enol ether (Scheme 4.35) [56]. The diastereomeric cycloadducts formed, 4-165 and 4-166 can be isolated in high yield. However, if R is hydrogen, an elimination process follows to give the acetals 4-167 in 56% yield. 

The starting aUylic nitro compound is obtained by nitration of 2-methylpropene with NOz. Subsequent Michael addition to methyl vinyl ketone followed by Pd-cataly zed ally lie alkylation affords terpenoids. 

The reduction of aromatic nitro compounds to amino derivatives and cyclizations to various heterocyclic compounds are presented in Chapter 9. Recent advances are presented here. Reaction of 2-nitrobenzaldehyde with vinyl carbonyl compounds in the presence of 1,4-diazbi-cyclo[2.2.2]octane affords Baylis-Hillman products, the catalytic reduction of which results in direct cyclization to quinoline derivatives (Eq. 10.78).134... 

Reduction of nitroalkanes RNO2 with samarium(II) iodide, obtained from samarium and 1,2-diiodoethane, yields either alkylhydroxylamines RNHOH or alkylamines RNH2, depending on the amount of the reagent434. The base-catalysed reaction of nitroalkanes with phenyl(vinyl) sulphoxide (399) yields the conjugate adducts 400, which fragment to allylic nitro compounds 401 on thermolysis435. 

With aldehyde donors, the reactions are generally syn selective. A range of acceptors can be used, including a,p-unsaturated nitro compounds [72, 270, 274-281], a,p-unsaturated ketones [71, 282-285], vinyl phosphonates [286] and vinyl sulfones [287] etc. (Scheme 27). So far, no general anti selective... 

Nickel, dichloro [ethylenebis(dimethyl-phosphine)], 58, 133 Nickel, dichloro[ethj lenebis(diphenyl-phosphine)], 58,133 [Ni (-)-diop Cl2 ], (-)-diop=2,3-0-iso-propylidene-2,3-dihydroxy-l,4-bis(di-phenylphosphino)butane, 58, 133 Nickel, dichloro [ trimethylenebis(diphenyl-phosphine)], 58,133 NITRILES, alkylation of, 55, 91 NITRILES FROM KETONES, 58, 101 NITRILES, a vinyl, 55, 99, 101 p-Nitrobenzenesulfonyl cyanide, 57, 89 p-Nitrobenzyl alcohol, 57, 72 p-NITROBENZYL FLUORIDE, 57, 72 Nitro compounds, 56, 36 Nitronates, 56, 36... 

Unsaturated Nitriles, Nitro Compounds, and Sulfonic Acids and Esters 2-33 Cyanation of vinylic organometallic compounds... 

Vinylpyrroles and vinylindoles are extremely sensitive to acid-catalyzed dimerization and polymerization and it is significant that much of the early research was conducted on systems which were produced in situ. Even by this approach, the dimerization of, for example, 2-(3-indolyl)propene and l-(3-indolyl)-l-phenylethylene was difficult to prevent (see the formation of 110 and 120, Section 3.05.1.2.8). Similarly, although it is possible to isolate ethyl 2-(2- and 3-indolyl)propenoates, they appear to be extremely unstable at room temperature even in the absence of acid (81UP30500) to give [ 4 + 2] cycloadducts of the type (348) (cf. 77JCS(P1)1204>. For many years simple vinylpyrroles also eluded isolation, on account of their facile acid-catalyzed polymerization. Application of the Wittig reaction, however, permits the synthesis of vinyl-pyrroles and -indoles under relatively mild and neutral conditions (see Section 3.05.2.5). In contrast, heteroarylvinyl ketones, esters, nitriles and nitro compounds, obtained by condensation of the appropriate activated methylene compound with the heteroaryl aldehydes (see Section 3.05.2.5), are thermally stable and... 

In contrast to carbenes, nitrene attacks only the carbon and never the sulfur atom of thiophene the only exception to this is discussed in Section 3.14.3.5. Unsubstituted thieno[3,2-/>]pyrrole and thieno[2,3-6]pyrrole have been prepared by thermolysis of the corresponding vinyl azides (Scheme 68) (81IJC(B)27l). A bis-cyclization of this type has also been reported (73CR(C)(277)1149>. Similarly, in the benzo[Z>jthiophene series the nitrene (252), generated either by thermolysis of the azide or by P(OEt)3 induced deoxygenation of the nitro compound, gives only the condensed indole (253) (79AG(E)900). 

CAUTION All operations should be conducted in an efficient fume cupboard owing to the toxicity of aliphatic nitro compounds and of alkyl vinyl ketones. 

Substitutions by the SRn 1 mechanism (substitution, radical-nucleophilic, unimolecular) are a well-studied group of reactions which involve SET steps and radical anion intermediates (see Scheme 10.4). They have been elucidated for a range of precursors which include aryl, vinyl and bridgehead halides (i.e. halides which cannot undergo SN1 or SN2 mechanisms), and substituted nitro compounds. Studies of aryl halide reactions are discussed in Chapter 2. The methods used to determine the mechanisms of these reactions include inhibition and trapping studies, ESR spectroscopy, variation of the functional group and nucleophile reactivity coupled with product analysis, and the effect of solvent. We exemplify SRN1 mechanistic studies with the reactions of o -substituted nitroalkanes (Scheme 10.29) [23,24]. 

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