Nitroarenes, arylation

The Bunce group disclosed a straightforward domino process for the construction of aryl-fused nitrogen heterocycles by employing a combination of a reduction and a Michael addition [20]. The transformation involves an initial Fe-mediated reduction of nitroarenes 7-38, furnishing an aniline which undergoes a subsequent... 

Tandem reduction-Michael addition using suitably substituted nitroarenes provides a general route to aryl-fused nitrogen heterocycles (Eq. 10.79).135... 

D Auria synthesized bispyrrole[3,2-A3, 2 -f ]dithianes such as 453 as part of the investigation of the photochemical reactions of aryl and heteroarylalkenes 452 in the presence of nitroarenes <1996T14253>. A number of rearrangements lead to the diradical intermediate 455, which then dimerizes to 453 (Scheme 34). 

This observation was made by Coon, in Reference 90. To the best of our knowledge, there are no experimental data for the enthalpy-of-formation difference of simple nitroarenes and aryl nitrites such as PhN()2 and PhONO. Given earlier enunciated complications regarding measurements of alkyl nitrites, we are not surprised by this gap in our knowledge. 

Quaternary ammonium salts aid the transfer of the hypophosphite anion in the palladium-catalysed reduction of, for example, alkynes to alkenes, nitroarenes to aminoarenes, and in the hydrogenolysis of tetrazolyl aryl ethers to phenols [12-14], It has been demonstrated that the hydrogenolysis is ineffective when preformed tetra-n-butylammonium hypophosphite is employed in a dry homogenous organic solvent [13, 14], For optimum hydrogen transfer, the concentration of hypophosphite relative to the substrate must be controlled at a low level and this is most effectively accomplished with a two-phase system. 

Stilbenes, photocyclization of, 30, 1 StiUe reaction, 50, 1 Stobbe condensation, 6, 1 Substitution reactions using organocopper reagents, 22, 2 41, 2 Sugars, synthesis by glycosylation with sulfoxides and sulfinates, 64, 2 Sulfide reduction of nitroarenes, 20, 4 Sulfonation of aromatic hydrocarbons and aryl halides, 3, 4 Swem oxidation, 39, 3 53, 1... 

Acceptor-substituted haloarenes have been successfully used to O-arylate phenols by aromatic nucleophilic substitution (Table 7.14). The most common arylating agents are 2-fluoro-l-nitroarenes, 2-halopyridines, 2-halopyrimidines, and 2-halotriazines. When sufficiently reactive haloarenes are used, the reaction proceeds smoothly with either the arylating agent or the phenol linked to the support. The thallium(III) nitrate catalyzed arylation of phenols with aryl iodides has been used for macrocycli-zations on solid phase [184], Burgess and co-workers have developed a solid-phase synthesis of 3-turri mimetics based on ring-closure by aromatic nucleophilic substitution (Entry 4, Table 7.14 see also Table 10.5). Phenols, alkylamines, and thiols have been successfully used as nucleophiles for this type of macrocyclization [185],... 

Displacement reactions with nitrite ion do not work well with aryl halides. However, displacement of the diazonium group is a practical route to nitroarenes (the Sandmeyer reaction), as described in Section 23-10B ... 

Nitrosoarenes give unstable diaryl hydroxylamines with aryl Grignard reagents, which can be reduced directly to diarylamines.312 Since arylmagnesium halides reduce nitroarenes to nitroso compounds, readily available nitroarenes and nitrohetarenes can be involved in this reaction allowing a simple preparation of polyfunctionalized diaryl- and heteroarylamines (Scheme 108).313... 

Finally, in sect. 2.9, the conversion of 2,4,6- or higher substituted pyrylium salts into the corresponding nitrobenzene derivatives through reaction with nitromethane 27) will be discussed in more detail. Since pyrylium salts of any desired complexity can be easily prepared 28), the conversion of the nitroarenes leads to a large number of phenols of the desired constitution. This method is by far the most versatile in the preparation of a desired arylated phenol. These syntheses, however, involve many steps. 

To our knowledge, reactions of organometallic compounds with nitroarenes lead, as a rule, to mixtures of reduction and alkylation (or arylation) products.2 11 Only few examples have been described where the reactions proceed with the formation of N, /V-disubstituted hydroxylamine and/or secondary amines.4-6-9... 

PtCl2(PPhj)2] in the presence of SnCU and EtsN, both in catalytic amounts, catalyzes the reduction of nitroarenes to aniline derivatives by CO and water (equation 74). SnCU was less effective. The reaction requires raised temperature and CO pressure. If alcohols were used in the same reaction in place of water, alkyl aryl carbamates were produced (equation 144). The catalyst precursor was again [PtCU(PPh3)2] with SnCU and EtjN. 

Bis(silyl)ketene acetals undergo silatropic ene reaction with nitrosobenzene to give N-hydroxyamino acid derivatives. When allylmagnesium chloride is reacted with nitroarenes, unstable adducts result. Reduction of these adducts with LAH in the presence of palladium on charcoal leads to A -allyl-W -aryl-hydroxylamines (73 Scheme 15). With alkyl Grignard reagents this reaction is negligible. ... 

Nickel. 12,355 13,197 It UUmann coupling. electrolysis of a DMF sola current, aryl halides underg Reduction of nitroam catalyst prepared by reduco nitroarenes are converted to Hydroindolone formnt alkaloids involves cyclizatit acid in refluxing isopropam MeOv... 

Reductions. In the reduction of organic compounds by Sm some additives are often included. For example, iodine is present in the system for the reduction of nitroarenes and aryl azides, and sodium alkyl thiosulfates.- ... 

Titanium(IV) chloride and titanocene dichloride have catalytic effects on the reduction, e.g., in the transformation of alkyl thiocyanates to dialkyl disulfides and nitroarenes to aryl amines, respectively. 

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