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

The reductive coupling reaction of 1,4-bis(3-acetyl-5-tert-butyl-2-methoxyphenyl)butane 3 was carried out using TiCl4-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 CH2Cl2 afforded the interesting compound 1,2-bis-(bromomethyl)-5,15-di-tert-buty1-8,18-dimethoxy[2.4]MCP-1-ene 6 and consecutive debromination with Zn and AcOH in CH2Cl2 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 chiral areno-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 mirror images of each other. (C) 2017 Elsevier Ltd. All rights reserved.