Planarized Triarylboranes: Stabilization by Structural Constraint and Their Plane-to-Bowl Conversion

Triphenylborane and 9,10-diphenyl-9,10-dihydro-9,10-diboraanthracene,
constrained to a planar arrangement with methylene tethers, were synthesized
by intramolecular multi-fold Friedel–Crafts cyclization. These
compounds were stable toward air, water, and amines, despite the absence
of steric protection in the vertical direction with respect to the
B atoms, and showed characteristic structural, electronic, and photophysical
properties. In addition, upon treatment with a fluoride ion, these
compounds underwent a plane-to-bowl conversion in a controlled manner.