Synthesis, structure and insertion reactivity of Lewis acidic 9-aluminafluorenes

9-Aluminafluorenes have only been sparingly investigated and their properties still remain largely unexplored. Herein, we report the synthesis of five aluminafluorene derivatives with a diverse array of aluminium substituents and probe their Lewis acid properties and reactivity. We show that 9-bromo-9-alu-minafluorene readily forms Lewis acid-base adducts with N-heterocyclic carbenes (NHCs), cyclic (alkyl)(amino)carbenes (CAACs) and pyridines and that it undergoes a selective ring expansion reaction with the iminoborane tBuN-BMes to give a seven-membered ring, which can be viewed as a boron-nitrogen analogue of alumepins.

Automated summary

In this study, synthesis of five aluminafluorene derivatives with diverse aluminium substituents was reported, and their Lewis acid properties and reactivity were probed. It was found that 9-bromo-9-aluminafluorene readily forms Lewis acid-base adducts with N-heterocyclic carbenes, cyclic (alkyl)(amino)carbenes, and pyridines, and undergoes a selective ring expansion reaction with iminoborane tBuN-BMes to give a boron-nitrogen analogue of alumepins.