Bridged Annulenes

The synthesis and aromaticity of 1,6‐methano[10]annulene and its analogues containing a heteroatom bridge suggested the possibility that the homologous series of bridged [4 n + 2]annulenes 1, 2, 3 , etc., formally derived from the acene series, could be developed. In the pursuit of this concept a set of systematically bent bridged [14]annulenes which permitted a scrutinization of the steric prerequisite of the Hückel rule — the requirement of a planar ring skeleton — were built up. Moreover, a new synthetic strategy based on the synthon cycloheptatriene‐1,6‐dicarboxaldehyde has provided access to the two next higher homologues (syn‐series) of 1,6‐methano[10]annulene, i.e., syn‐1,6:8,13‐bismethano[14]annulene and syn, syn‐1,6:8,17:10,15‐trismethano[18]annulene, respectively.