Reversible Boron‐Insertion into Aromatic C−C Bonds

Abstract

Formation of borabicyclo[3.2.0]heptadiene derivatives was achieved via boron‐insertion into aromatic C–C bonds in the photo‐promoted skeletal rearrangement reaction of triarylboranes bearing an ortho‐phosphino substituent (ambiphilic phosphine‐boranes). The borabicyclo[3.2.0]heptadiene derivatives were fully characterized by NMR and X‐ray analyses. These dearomatized products were demonstrated to undergo the reverse reaction in the dark at room temperature, realizing photochemical and thermal interconversion between triarylboranes and boron‐doped bicyclic systems.Experimental and theoretical studies revealed that sequential two electrocyclic reactions involving E/Z‐isomerization of an alkene moiety proceed via a highly strained trans‐borepin intermediate.