ipso Nitration. XXVI. Nitration of 1,2-dimethyl-4-nitrobenzene. Formation and reactions of adducts

Abstract

Nitration of 1,2-dimethyl-4-nitrobenzene in a mixture of acetic anhydride and trifluoroacetic anhydride gives the diastereoisomers of 4,5-dimethyl-2,4-dinitrocyclohexa-2,5-dienyl acetate (50%), in addition to the 1,2-dimethyldinitrobenzenes. In moderate and more strongly acid conditions the adduct gives 4-nitro-, 3,4-dinitro-, and 3,5-dinitro-o-xylene. In neutral and weakly acid solutions 4-nitro- and 3,5-dinitro-o-xylene are formed by a radical and a sigmatropic pathway. The adduct reacts facilely with nucleophiles by allylic substitution to give a 5,6-dimethyl-6-nitrocyclohexa-2,4-dienyl derivative which, in many instances, undergoes a second allylic substitution to a new 4,5-dimethyl-2,4-dinitrocyclohexa-2,5-dienyl derivative. Depending on the nature of the introduced substituent, these 2,4- and 2,5-dienyl products may eliminate nitrous acid, under the reaction conditions, to give the corresponding aromatic compound. The dienyl acetates undergo acid-catalysed transesterification to the corresponding dienols.