Escape from Flatland: Stereoselective Synthesis of Hexa-aryl Borazines and their sp²-Based 3D Architectures.

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Borazine and its derivatives can be considered critical doping units for engineering hybrid C(sp2)-based molecules with tailored optoelectronic properties. Herein, we report the first synthesis ofhexaarylborazines that, bearingortho-substituted aryl moieties, extend three-dimensionally.Using a one-pot protocol, we first form an electrophilic chloroborazole and then react it with an aryl lithium (ArLi). By selecting the appropriateortho-substituent, we can guide the ArLi to add to the BN-core in a specific way, ultimately controlling the stereochemical outcome of the three-substitution reaction. Rationalization of the stereochemical model through computational analysis allowed us to show thatwhen aryl lithium nucleophiles bearing rigid long-rangeortho-substituentsare used,i.e.,stiff substituents. Theortho-substituent shields its side of the electrophilic B3N3core, biasing the incoming ArLi to addantiat each addition step, forming the final tri-aryl borazine exclusively ascc-isomer.Leveraging this stereoselective approach, prototypical multichromophoric borazine derivatives were prepared, and we showcased how the stereochemical arrangement of these chromophores distinctly influences their redox behavior.This methodology paves the way for previously inaccessible borazines to serve asprivileged precursorsto transcend the conventional bidimensionality associated with graphenoid systems and pioneer the construction of new forms of three-dimensional C(sp2)-based architectures.