Revisitation of Cycloheptatriene Derivatives as a Building Block for Various Substituted and Fused 1,6-Methano[10]annulenes and Substituted 4,9-Methanothia[11]annulenes

A synthetic maneuver from 1,6-diacetyl- and 1,6-diformyl-1,3,5-cycloheptatrienes toward various 1,6-methano[10]annulenes, such as diaryl-substituted, cyclobutene-annulated, and thiophene-annulated derivatives and its quinodimethane-type compound, and 4,9-methanothia[11]annulenes is spotlighted based on our recent research efforts. The crystal structure analysis of the annulenes, discussion of mechanistic details of a key cyclization step and application of some annulene derivatives to a material in organic electroluminescent devices are also described.