NorwichProton magnetic resonance is used to study the tautomeric equilibria of a number of methyl-substituted benzofuroxans and pyrido r2,3-c]furoxans. Large influences (ca. 0.5-1 kcal./mole) are exerted by methyl and azasubstituents adjacent to the heterocyclic ring.EXTENSIVE studies from this laboratory and elsewhere have shown that benzofuroxan exhibits a rapid tautomeric rearrangement [(I) =+= (II)].2 The effects of 4-and 5-substituents t on this equilibrium are known for a series of 5-monosubstituted derivatives; for other related work see ref. 2. The present work is concerned with the effect of the methyl and aza-substituents. Previously, long-range couplings have hindered detailed interpret ation of low-t emperature methylbenzof uroxan ~p e c t r a ,~ and azabenzofuroxans (pyridofuroxans) have been difficult to prepare. We have sought new synthetic routes and have applied decoupling techniques to simplify the spectral analyses.Benzofuroxans in this paper are =umbered throughout as in (I) and (11). Where a tautomeric pair of compounds is being considered it is usually referred to by assigning to the substituent(s) the lowest numerical value(s) . Pyridofuroxans are named as azabenzofuroxans for clarity.Part XXXVI, A.The effect of a 5(6)-methyl group is small.
Preparation of Com~ozcnds.-2-Azido-3-nitrotoluenedid not yield 4-methylbenzofuroxan on pyrolysis ; in this it resembled other sterically hindered azides.5 Attempted 0-iodosobenzene diacetate oxidation of 2-amino-3-nitrotoluene also failed (contrast its successful use 6 with the 3,2-isomer) but pyrolysis of 3-azido-2-nitrotoluene succeeded.The preparation of 4-azabenzofuroxan by pyrolysis of 4 G. Englert,
The nitration of 2-pyridone yields largely the 3-nitro-derivative in low acidity media and largely the 5-nitro-compound in high acidity media. However, both reactions occur on the free base species. This behaviour is compared with similar phenomena in the literature.
Norwich NOR 88CRECENTLY, we studied the kinetics for the nitration of 3-methyl-2-pyridone in the 5-position and for 5-methyl-2pyridone in the 3-position: the rate constants for these two nitrations showed significantly different dependence on the acidity of the nitration medium. Raising the acidity appeared to increase the relative rate of nitration at the 5-position. In connection with other workJ3 we found that the proportion of the 3-and 5-nitro-derivatives formed in the mono-nitration of 4-methyl-2pyridone did indeed vary considerably with the condi-
Abstract-NMR spectral parameters are reported for benzofurazan, 1,2,3-and 2,1,3-benzothiadiazole, and I-methyl-and 2-methyl-benzotriazole. The coupling constants are discussed in conneG tion with the aromaticity of these compounds and the occurrence of partial bond fixation.THE orrho-proton-proton coupling constants in six-membered ring aromatic compounds depend on r-bond order. For carbocyclic aromatic systems, the empirical relation (1) between JOrtho and the r-bond order, P, has been suggested.2 The orthocoupling constants J = 12.7P -1.1 for naphthalene (1)3 and biphenylene (2)4 mirror the well-established partial bond fixation in the senses indicated, and quantitatively the J values are in fair agreement with equation (1) (for 1 calculated5 8.1, 6.6Hz; for 2 calculated5 6-8, 7.7 Hz). More recent work6 has extended the range of equation (I) at both ends and suggested its modification to (2).The present work is an extension of such reasoning to heterocyclic compounds, and we now report the investigation of the series 3 and 4 where Z = 0, S, and NMe.
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