Synthesis of CH₂‐Bridged [4n + 2]Annulenes by a Building‐Block Approach

Abstract

Homologous series of syn‐bridged annulenes are of interest for a deeper understanding of the Hückel rule. Dialdehydes like (3) could be key compounds for syntheses of such annulenes. The synthesis of (3) from the dialdehyde (1) was accomplished in three steps: reaction with (2) to give the diester, reduction to the diol, and oxidation to (3). This three‐step sequence is also suitable for synthesis of the two next higher dialdehydes with three and four CH2 groups, respectively.

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

“…It is worthy to note that access to 2 is not difficult; 2 can be prepared from commercially available 1,3,5-cycloheptatriene by two acetylations in a hundred-gram scale. This sequence provided an important pathway to the 3-and 3,4-substituted annulenes, and thus diformyl compound 3 was also found to be a very versatile synthetic intermediate for preparing various bridged annulenes, such as muliti-bridged annulenes [6]. 1,6-methano [10]annulenes described in this review.…”

“…Treatment of 8b, c, and e with a catalytic amount of p-toluenesulfonic acid (p-TsOH) in refluxing benzene for 0.5-1.5 h gave 2,5-disubstituted 2,3dihydro-1,6-methano [10]annulenes 11b, c, and e in good to high yields and 8d with pyridinium p-toluenesulfonate (p-TsOHPy) in refluxing benzene for 20 h gave 11d in high yield. It is naturally considered that these reactions are initiated by double dehydration to afford 1,6bis(1-substituted vinyl)cyclohepta-1,3,5-trienes 9, which undergo electrocyclization at the termini of their vinyl groups to give 2,5-disubstituted 3,4-dihydro-1,6methano [10]annulenes 10 as seen in the experiments by Vogel et al [6]. On the other hand, the diol 8a under the acidic reaction conditions afforded an unseparable mixture of 11a and 12a, accompanied with a substantial amount of unidentified products.…”

“…Annulene 1 was synthesized from tetrahydronaphthalene in 4 steps (Scheme 1) at first [2,3]. Later on, Vogel et al reported an alternative synthetic route to 1 and its 3-and 3,4-substituted derivatives starting from the title 1,6-diacetyl-1,3,5-cycloheptatriene (2 ) as summarized in Scheme 2 [6]. Later on, Vogel et al reported an alternative synthetic route to 1 and its 3-and 3,4-substituted derivatives starting from the title 1,6-diacetyl-1,3,5-cycloheptatriene (2 ) as summarized in Scheme 2 [6].…”

Iridium Chemistry of 1,6-Bis((tert-butylphosphino)methyl)-1,3,5-cycloheptatriene

“…Compound 1 was synthesized from 1,6-dibromomethylcycloheptatriene, which was prepared from the corresponding diol and PBr 3 . The diol was synthesized according to procedures described by Vogel and Darms. − …”

syn,syn‐1,6:8,17:10,15‐Trismethano[18]annulene

“…Indeed, (12) afforded the annulene when it was thermolyzed (yield 40 %; after chromatography) with DDQ (molar ratio 1 : 1. 4) in anisole (quartz ampoule; 270°C, 7 min). Attempts to detect (13), the dihydro[18]annulene precursor of (3), have so far failed.…”