Nucleophilic aromatic substitution 2-nitrofurans

Such nucleophilic displacements are likely to be addition-elimination reactions, whether or not radical anions are also interposed as intermediates. The addition of methoxide ion to 2-nitrofuran in methanol or dimethyl sulfoxide affords a deep red salt of the anion 69 PMR shows the 5-proton has the greatest upfield shift, the 3- and 4-protons remaining vinylic in type.18 7 The similar additions in the thiophene series are less complete, presumably because oxygen is relatively electronegative and the furan aromaticity relatively low. Additional electronegative substituents increase the rate of addition and a second nitro group makes it necessary to use stopped flow techniques of rate measurement.141 In contrast, one acyl group (benzoyl or carboxy) does not stabilize an addition product and seldom promotes nucleophilic substitution by weaker nucleophiles such as ammonia. Whereas... 

Sensitivity precludes the use of concentrated acid nitrating mixtures. Reaction of furan, or substituted furans" with acetyl nitrate produces non-aromatic adducts, in which progress to a substimtion product has been interrupted by nucleophilic addition of acetate to the cationic intermediate, usually at C-5. Aroma-tisation, by loss of acetic acid, to give the nitro-substitution product, will take place under solvolytic conditions, but is better effected by treatment with a weak base, like pyridine. " Further nitration of 2-nitrofuran gives 2,5-dinitrofuran as the main product. ... 

---