TOWARDS GREENER MECHANOSYNTHESIS OF FUNCTIONAL CALIXARENES

The awareness for sustainability led to an increasing global demand for processes that use lower energy, produce reduced waste, use fewer organic solvents and offer improved selectivity. In this context, mechanochemistry reemerged as a powerful green methodology. Besides matching all these requirements, a major advantage and an extraordinary feature of mechanosynthesis is the elimination of solubility issues, thus ensuing chemical transformations by simple, mostly solventless, grinding. Moreover, mechanochemistry is a truly new synthetic tool, by allowing the access to products otherwise found possible only in classical solution reactions. Nevertheless, and despite great achievements made in the last few years, the field of mechanosynthesis is still rather unexplored.

Calixarenes are synthetic macrocycles that are among one the most interesting 3D structures, like cucurbiturils and dendrimers. Presenting considerable functional and tunable diversity, its synthesis and functionalization is highly defying. The conventional synthesis and functionalization of calix[4]arenes, both on the upper and lower rim, has been the subject of numerous studies, however only a few were reported using mechanochemical approach.

Herein, we present for the first time a new mechanically assisted key synthetic steps towards a more sustainable route to several calix[4]arenes derivatives functionalized in the lower rim (e.g. p-iodobenzyl derivatives) to be used as functional precursors toward the synthesis of conjugated polymers by Sonogashira-Hagihara cross-coupling.

The syntheses were performed in a planetary ball mill using a zirconium oxide reactor, under solventless conditions, with good yields and much lower reaction times, in comparison with conventional methods.