Diene intermediates in the acetoxylation of o-xylene

. 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 ...

Section: Resultssupporting

confidence: 76%

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

Fischer¹,

Henderson²,

Iyer³

1985

“…Nitration in acetic anhydride of aromatic compounds in which a substituted position is of a comparable or greater degree of activation than an unsubstituted position often leads to the formation of nitronium acetate adducts (1,2) in which the nitro group is attached to the activated substituted (ipso) position. Most commonly the 1,4 adduct is formed, normally as a pair of diastereomers.…”

mentioning

confidence: 99%

ipso Nitration. XXVII. The crystal structure and stereochemistry of 3-bromo-6-methyl-6-nitrocyclohexa-2,4-dienyl acetate, 5-bromo-2-methyl-6-nitrocyclohexa-2,4-dienyl acetate, and 3-bromo-6-methyl-6-nitrocyclohexa-2,4-dienyl chloride

Bushnell¹,

Fischer²,

Henderson³

et al. 1986

The adduct obtained on nitration of 4-bromotoluene in acetic anhydride is (Z)-3-bromo-6-n1ethyl-6-nitrocyclohexa-2,4-dienyl acetate. Its stereoselective rearrangement product, obtained on thermolysis in the presence of p-cresol, is (2)-5-bromo-2-methyl-6-nitrocyclohexa-2,4-dienyl acetate. Reaction with hydrogen chloride in ether is also stereospecific and gives (2)-3-bromo-6-methyl-6-nitrocyclohexa-2,4-dienyl chloride. The crystal structures of these compounds are reported.

“…Other arenes which have been shown to give tertiary acetate adducts are 1,2,4-trimethylbenzene (pseudocumene) (8) and the tetramethylbenzenes (2). Toluene (9) and o-xylene (10) give secondarv acetate adducts. The dominant redride gave 59y0 of diene adducts and 4176 of 4-tert-butyl-2-nitrotoluene.…”

Section: Introductionmentioning

confidence: 99%

Nitration of p-tert-butyltoluene in acetic anhydride. 1,2 and 1,4 adducts

Fischer¹,

Röderer²

1976

Nitration of p-tert-butyltoluene in acetic anhydride gives 5-tert-butyl-2-methyl-2-nitro-1,2-dihydrophenyl acetate (43%), cis- and trans-1-tert-butyl-4-methyl-4-nitro-1,4-dihydrophenyl acetate (16%) and 4-tert-butyl-2-nitrotoluene (41%). Reaction of either of the 1,2 or 1,4 nitroacetoxy adducts with hydrogen chloride gives a mixture of the 1,2 and 1,4 nitrochloro adducts. The 1,2 (secondary) acetate adduct eliminates nitrous acid to form 5-tert-butyl-2-methylphenyl acetate under mildly acidic conditions. Under more vigorously acidic conditions 4-tert-butyl-2-nitrotoluene is formed. The same products are formed from the 1,4 (tertiary) acetate adducts but p-tolyl acetate is also obtained. The 1,2 and 1,4 adducts couple with anisole to form 5-tert-butyl-4′-methoxy-2-methylbiphenyl.