Directed functionalization of aromatic and heteroaromatic nitriles using the base TMPMgCloLiCl

The regio- and chemoselective functionalization of arenes and heterocycles using organometallic reagents has been an important synthetic tool in the synthesis of new bioactive molecules, as well as in materials chemistry. In this context, the objective of this study was to investigate the reactivity of new mixed magnesium-lithium reagents in the functionalization of aromatic nitriles (dicyanobenzene) and heteroaromatic (furan, thiophene, pyridine and pyrazine), whereas the cyano group is an important synthetic intermediate and can be transformed into various functional groups. For all substrates, methodological trials were performed in order to stablish the best reaction conditions of metalation using organometallic base TMPMgCloLiCl in the presence or absence of additives such as ZnCl2. After formation of the magnesiated intermediated, reactions were quenched with several electrophiles, leading to the desired products in good yields. Following a transmetalation step with ZnCl2, intermediates could be arylated using Negishi cross-coupling reactions. Moreover, the metalation study using nitrile-substituted furan and thiophene substrates resulted in functionalized heterocyclic nitriles in good yields. Similarly, the functionalization of pyridines and pyrazines with TMPMgCloLiCl were also evaluated using both conventional conditions and under microwave irradiation in the metalation step. After that, the treatment of the corresponding organomagnesium intermediates with various electrophiles provided functionalized pyrazines and pyridines with interesting chemo- and regioselectivity and in moderated yields. Finally, the reactivity of cyano- and dicyanobenzenes against the base TMPMgCloLiCl was also evaluated, however in this case the organolithium reagents appeared to be more efficient for the functionalization of this class of compounds (AU)