Gallepins. Neutral Gallium Analogues of the Tropylium Ion: Synthesis, Structure, and Aromaticity

摘要

On the basis of its expected 6π-electron aromatic system, Doering and Knox proposed the tropylium ion (cycloheptatrienyl cation) structure for the intriguing species first observed by Merling in 1891. The chemistry of the analogous borepins, a class of neutral isoelectronic seven-membered rings with a boron atom in the cycloheptatrienyl framework, constitute a substantial body of work. Depending on the nature and degree of substitution, borepins may adopt either a boatlike or a planar conformation. The aromatic nature of borepins has been extensively investigated.