Synthesis, Characterization, and Functionalization of 1‐Boraphenalenes

1‐Boraphenalenes have been synthesized by reaction of BBr(3) with 1‐(aryl‐ethynyl)naphthalenes, 1‐ethynylnaphthalene, and 1‐(pent‐1‐yn‐1‐yl)naphthalene and they can be selectively functionalized at boron or carbon to form bench‐stable products. All of these 1‐boraphenalenes have LUMOs localized on the planar C(12)B core that are closely comparable in character to isoelectronic phenalenyl cations. In contrast to the comparable LUMOs, the aromatic stabilization of the C(5)B ring in 1‐boraphenalenes is dramatically lower than the C(6) rings in phenalenyl cations. This is due to the occupied orbitals of π symmetry being less delocalised in the 1‐boraphenalenes.