From aryl nitro compounds

The second example of a cine-substitution of a thiophene involves the reaction of arylthiolates with 3,4-dinitrothiophene (331) or 3-nitro-4-phenylsul-fonylthiophene (332) to give the 2,4-substituted products 333. Both an elimination-addition mechanism via the aryne (334) or an abnormal addition-elimination (AEa) mechanism (Section II.2.A.e) via the Meisenheimer complex (335) have been considered for these reactions. The former is unlikely for several reasons including the lack of precedence for aryne formation from aryl nitro compounds (Section II. 1) under these reaction conditions and the fact that addition of the nucleophile ArS" to the aryne (334) would have to proceed via the 3-thienyl anion (336) rather than via a more stable 2-thienyl anion such as 320 as would be expected. Contrariwise, cine-substitution by the AEa mechanism is favored by the ability of the complex (335) to stabilize the negative charge by delocalization to both the NO2 group and the a position of the thiophene ring." As in the pyrrole series (Section III.2.B) the actual mechanism appears to be more complex, however, involving several addition and elimination steps via 337, which was recently isolated from the reaction (X = NO2) and shown to go to the product 333 under the reaction conditions. It therefore appears that neither of the cine-substitutions of thiophene described in this Section proceeds via an aryne intermediate. 

Figure 8, Photolytic generation of nitrogen dioxide and an aryl nitrite ester from a nitro compound, as formulated by Lippert and Kelm (27),...

Scheme 4. The compounds and intermediates on the rear plane of the bicubic system (farthest from the reader) are protonated on the pyridine nitrogen atom those on the front plane (nearest the reader) are not. Laviron s work has shown that the reduction of 14 and its corresponding N-oxide34, and indeed probably most aryl nitro compounds, proceeds by an ECEC sequence leading to the neutral N,N-dihydroxy [ArN(OH)2] intermediate at all proton concentrations from Ho = —6 to pH 9.6. This substance then loses water to form the nitroso compound, which then undergoes a second sequence leading to the arylhydroxylamine.

The method appears limited to aryl-substituted acyclic105-109 and cyclic110 alkenes and should be compared with the direct procedure for preparing //-nitro acetates from //-nitroso nitro compounds (Section 7.2.1.5.1). 

Polymer-supported enzymes have been combined with polymer-supported reagents in the synthesis of the bryostatins. The nitrone derived from the nitro compound 43 supported on a soluble aryl poly-ether polymer undergoes an efficient 1,3-dipolar cycloaddition with butenone to give the isoxazoline 44 and hence by reduction the racemic syn compound 45 required for the synthesis.16... 

This is most practically carried out via the use of aryl diazonium salts (Ar-N2 Cl ) which are derived from aryl amines(Ar-NH2) which are themselves produced by the catalytic reduction of aryl nitro compounds (Ar-N02). Thus, we would seem to need to put a nitro group para to the original hydroxyl group. We must be aware of phenol s immense reactivity and the subsequent danger of polynitration. To avoid this danger, we treat phenol with dilute nitric acid instead of with concentrated nitric acid and with concentrated sulfuric acid as the catalyst. 

Miscellaneous. Fluoride ion from anhydrous TBAF undergoes nucleophilic displacement of tosylates, halides, and aryl nitro compounds to give fluorinated products. When used with N-Bromosuccinimide, bromofluorination products are obtained. ... 

Arylisoxazol-5(4//)-oncs 21 react with benzene-1,2-diamines to yield 4-aryl-l,5-benzodiaze-pinones 22 by elimination of hydroxylamine from the intermediate oximes. Unsymmetrically substituted benzene-1,2-diamines are attacked at the more nucleophilic amino group. Thus, 4-methylbenzene-1,2-diamine gives 7-methylbenzodiazepinones 22f-h, whereas 4-nitrobenzene-1,2-diamine gives 8-nitro compounds 22k-n. The benzodiazepinones are accompanied by minor amounts of 2-methylbenzimidazoles 23. Selected examples are given.275... 

It was demonstrated (83) that the reaction of dinitrostyrenes (28) with aryl diazo compounds RR CN2 afford nitronates (24 g) in good yields. These products contain the nitro group at the C-4 atom in the trans position with respect to the substituent at C-5 (if R =H). Since the reaction mechanism remains unknown, the direct formation of cyclic nitronates (24 g) from pyrazolines A without the intermediate formation of cyclopropanes also cannot be ruled out. 

---