Unsaturated boron-containing heterocycles such as borirenes (I),[1] boroles (II),[2] and borepins (III)[3] have attracted fundamental interest owing to their electronic structure. The interaction of the empty pz orbital at boron in these systems with the unsaturated carbon backbone might result in a stabilization (I and III) or destabilization (II) of the entire π system, depending on the number of available π electrons. In particular, boroles (II) are of interest ...
