Rhombic Cyclobutadiene with a Boryl/Amino-Substitution Pattern: Boryl Group Migration Induced by Reaction with Water

The synthesis of a donor–acceptor
cyclobutadiene featuring
a boryl/amino-substitution pattern is presented together with its
characteristic reactivity toward water. On the basis of the results
of X-ray crystallography, theoretical studies, and spectroscopic analyses,
the observed rhombic structure of the cyclobutadiene was attributed
to a charge-separated electronic structure. Reaction of this boryl-substituted
cyclobutadiene with water induced a characteristic migration of the
boryl group, due to the Lewis acidity of the boryl-substituent.