Nitrated alkylaromatics are an important class of compounds and are utilised as intermediates in many high-volume industrial processes. This poster describes an approach to the regiospecific labelling of these systems by exploiting the differences in acidity between their aromatic and benzylic protons. In alkylnitroaromatics the benzylic protons are rendered particularly acidic by the presence of electron withdrawing nitro-substituents in the aromatic nucleus. Hence the compounds should be amenable to labelling if the appropriate anion can be generated in the presence of a suitable deuterium donor. We have investigated the labelling using deuterium oxide as the isotope donor in the presence of a various bases and aprotic cosolvents.

In the case of dinitro-alkylaromatics, a carefully selected tertiary amine base proved ideal, yielding, in the absence of oxygen, an effective labelling reaction at room temperature. E.g. 2,4-dinitrotoluene (pKa 15.3) exchanges easily, regiospecifically and with high atom% abundance under catalysis by triethylamine (pKa 10.8) without any of the expected complications due to the formation of the Meisenheimer complex.

Although the reaction of dinitro-systems is particularly facile, mono-nitro compounds with the alkyl substituent ortho or para to the nitro group can also be smoothly labelled using this approach provided that a stronger base, a longer reaction time and a higher temperature are applied. In this case a typical procedure utilises DBN base at 95^oC degrees for 18h.

Overall we have examined the relative labelling propensities of a range of alkyl mono-nitroaromatics and two alkyl dinitro-aromatics under various conditions. Our results show clear effects of the substitution pattern and of the stereochemical orientation of the nitro and alkyl substituents upon the extent and ease of labelling. The poster will discuss these effects in addition to providing efficient protocols for the labelling of both mono- and dinitro-systems.