2- Nitro-5- furan, reduction

These compounds are less common than indole (benzo[ ]pyrrole). In the case of benzo[i>]furan the aromaticity of the heterocycle is weaker than in indole, and this ring is easily cleaved by reduction or oxidation. Electrophilic reagents tend to react with benzo[Z ]furan at C-2 in preference to C-3 (Scheme 7.21), reflecting the reduced ability of the heteroatom to stabilize the intermediate for 3-substitution. Attack in the heterocycle is often accompanied by substitution in the benzenoid ring. Nitration with nitric acid in acetic acid gives mainly 2-nitrobenzo[Z ]furan, plus the 4-, 6- and 7-isomers. When the reagent is in benzene maintained at 10 °C, both 3- and 2-nitro[ ]furans are formed in the ratio 4 1. Under Vilsmeier reaction conditions (see Section 6.1.2), benzo[Z ]furan gives 2-formylbenzo[6]furan in ca. 40% yield. 

Nitroaromatic compounds (e.g. nitroimidazoles and nitro-furans) are useful against anaerobic microbial infections (1). They are also differentially toxic towards anaerobic or hypoxic mammalian cells (2) and selectively radiosensitize hypoxic cells, offering a potential new use for nitro compounds in cancer radiotherapy (3,4). The selective toxicity, i.e. the protection by O2, may arise via the one-electron transfer reaction (T), since the nitro radicals, RNO2 have been observed in anaerobic microsomal incubations (5) and the anaerobic reduction products such as hydroxylamines probably lead to cytotoxicity by binding to DNA and RNA (6) ... 

Benzo[b]furan, 2-nitro-reduction, 4, 74, 647 Benzo[b]furan, 5-nitro-mass spectrometry, 4, 583 Benzo[b]furan, 2-(4-nitrophenyl)-properties, 4, 708 Benzo[b]furan, 2-phenyl-bromination, 4, 605 chloromethylation, 4, 607 nitration, 4, 604 photochemical reactions, 4, 636 properties, 4, 697 Benzo[b]furan, 3-phenyl-synthesis, 4, 697... 

That product (17) is then converted to the activated A -hydoxysuccinimide derivative 18 as in the case of the monocyclic furan. Reaction with the primary amine 10 used to prepare amprenavir then leads to the urethane (19). Reduction of the nitro group then affords darunavir" (20). 

The reaction is most useful for the preparation of olefinic, halo, and nitro alcohols from the corresponding substituted aldehydes and ketones. These substituents ate very often affected by other reduction procedures. Excellent directions are found in the preparations of crotyl alcohol (60%), l-bromo-5-hexanol (64%), l-chloco-4-pentanol (76%), /S,/S,/S-trichloroethyl alcohol (84%), methyl-p-chlorophenylcarbinol (81%), and o-nitrobenzyl alcohol (90%). The reaction has also been used in the preparation of certain tetralols and decalols as well as 9-fluo-renylcarbinol (50%). The thiophene and furan nuclei are not reduced. 

Several furan aldehydes and ketones without a heterocyclic nitro group have been investigated polarographically and the intervention of ketyl radicals or their conjugate acids confirmed. Their involvement in amalgam reductions of furan carbonyl derivatives was also shown. 

Extension166-166 to pyrrole- and selenophene-2-carboxylic acids gives a sequence of sensitivity in the order pyrrole, furan, selenophene, thiophene, benzene, the same order as that observed by Tirouflet et al.ul in the polaro-graphic reduction of nitro derivatives of these rings. A different sequence, however, which correlates better with ground state aromatic character , viz., furan, pyrrole, thiophene, benzene, has been observed in the gas-phase ionization process,168 but results for electrophilic substitution appear to be anomalous.169... 

The direct detection of a variety of simple carbohydrate compounds by u.v. methods is mentioned in reference 7 above. Spectrophotometry has also been used to determine ketoses (as furan derivatives and glucose by its reduction of 3,5-dinitrosalicylic acid to the 3-amino-5-nitro analogue. ... 

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