Synthesis and structure of a chiral areno-bridged [2.4]metacyclophane

Abstract The reductive coupling reaction of 1,4-bis(3-acetyl-5- tert -butyl-2-methoxyphenyl)butane 3 was carried out using TiCl 4 -Zn in pyridine followed by a McMurry coupling reaction to afford the compounds anti and syn 1,2-dimethyl[2.4]MCP-1-ene 4 . Bromination of 4 with BTMA-Br 3 in dry CH 2 Cl 2 afforded the interesting compound 1,2-bis-(bromomethyl)-5,15-di- tert -butyl-8,18-dimethoxy[2.4]MCP-1-ene 6 and consecutive debromination with Zn and AcOH in CH 2 Cl 2 solution afforded the stable solid 5,15-di- tert -butyl-8,18-dimethoxy-1,2-dimethylene[2.4]MCP 7 in 89% yield. Compound 7 was conveniently employed in a Diels–Alder reaction with dimethyl acetylenedicarboxylate(DMAD) to provide 2-(3′,6′-dihydrobenzo)-5,15-di- tert -butyl-8,18-dimethoxy[2.4]MCP-4′,5′-dimethylcarboxylate 8 in good yield. Diels–Alder adduct 8 was converted into a novel and inherently chiralareno- bridged compound[2.4]MCP 9 by aromatization. The chirality of the two conformers was characterized by circular dichroism (CD) spectra of the separated enantiomer which are perfect mirrorimages of each other.