Rearrangement von Richter

When aromatic nitro compounds are treated with cyanide ion, the nitro group is displaced and a carboxyl group enters with cine substitution (p. 854), always ortho to the displaced group, never meta or para. The scope of this reaction, called the von Richter rearrangement, is variable. As with other nucleophilic aromatic substitutions, the reaction gives best results when electron-withdrawing groups are in ortho and para positions, but yields are low, usually < 20% and never > 50%. 

It may be noted that 16 are stable compounds hence it should be possible to prepare them independently and to subject them to the conditions of the von Richter rearrangement. This was done and the correct products are obtained. Further evidence is that when 15 (Z=C1 or Br) was treated with cyanide in H O, one-half the oxygen in the product was labeled, showing that one of the oxygens of the carboxyl group came from the nitro group and one from the solvent, as required by this mechanism. ... 

In an abnormal von Richter rearrangement, 2,6-dimethyl-3-nitropyridine reacts with potassium cyanide in methanol to give a mixture of 3-methoxy-6-methylpyridine-2-carbonitrile 1-oxide and 6,8-dimcthylpyrido[3,4-ring carbon in the 2-position of the pyrido[3,4-e ]pyrimidine originates from the 2-methyl group of the educt.420... 

The von Richter reaction, also known as the von Richter rearrangement, was first disclosed in 1871 and the results were revised in 1875 to reflect the correct regiochemistry of the benzoic acid products. The reaction was largely ignored until the mid-20 century "when it was further examined in a series of critical experiments that lead to a fuller understanding of the scope and ultimate elucidation of the mechanism. The reaction has been of limited synthetic value due to the low isolated yield of the products. 

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