. 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-die 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-die 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. ALFRED FISCHER, GEORGE N. HENDERSON et LOKANATHAN M. IYER. Can. J. Chem. 63, 2390Chem. 63, (1985. La nitration du dimtthyl-1,2 nitro-4 benzkne dans un mtlange d'anhydride acCtique et d'anhydride trifluoroacCtique conduit, en plus des dimtthyl-1,2 dinitrobenzknes, a la formation des diasttrtoisomkres de I'acktate du dirnkthyl-4,5 dinitro-2,4 cyclohexadikne-2,5 yle (50%). Dans des milieux modtrtment et plus forternent acides, I'adduit conduit aux nitro-4, dinitro-3,4 et dinitro-3,5 o-xylknes. Dans des milieux neutre ou Itgkrement acide, les nitro-4 et dinitro-3,5 o-xylknes se foment par un mtcanisme radicalaire suivi d'une transposition sigmatropique. Par substitution allylique, I'adduit rtagit facilement avec les nucltophiles et il conduit un dtrivt dimtthyl-5,6 nitro-o cyclohexadikne-2,4 yle qui, dans plusieurs cas, subit une deuxikme substitution allylique pour conduire i un nouveau dtrivt dirntthyl-4,5 dinitro-2,4 cyclohexadikne-2,5 yle. Dtpendant de la nature des substituants introduits, ces produits dikne-2,4 (ou -2,5) yles peuvent Climiner de I'acide nitreux dans les conditions de la rkaction &in de conduire i la formation du compost aromatique correspondant. Les acttates de dienyles subissent des transesttrifications acido-catalystes conduisant aux ditnols correspondants.[Traduit par le journal]Nitration at a substituted position, ipso nitration (3), is competitive with nitration at an unsubstituted position in many aromatic compounds. The resulting ipso-nitrocyclohexadienyl cation is captured as a relatively stable acetate ester in acetic anhydride and can be isolated. In previous work the adduct from 3,4-dimethybenzonitrile has been obtained (4). The nitro group has directing and deactivating effects similar to those of the cyano group and it was anticipated that nitration of 1,2-dimethyl-4-nitrobenzene (4-nitro-o-xylene) would occur at the 2 position, ipso to methyl, to form an adduct.
Results and discussion4-Nitro-o-xylene did not react at all when it was treated with nitric acid (5 mol ratio) in ...