Synthesis, structural properties, electrophilic substitution reactions and DFT computational studies of calix[3]benzofurans

Md Monarul Islam, Thamina Akther, Yusuke Ikejiri, Taisuke Matsumoto, Junji Tanaka, Shofiur Rahman, Paris E. Georghiou, David L. Hughes, Carl Redshaw, Takehiko Yamato

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Abstract

Calix[3]benzofurans have been synthesized by a modified TosMIC coupling reaction, followed by acid treatment and an intramolecular cyclization reaction with TMSI (trimethylsilyl iodide); X-ray analysis established the structures of two samples, both showing a cone conformation. 1H NMR spectroscopic analyses of the calix[3]benzofurans reveal that they can adopt drastically different conformations in solution and undergo very fast conformational changes relative to the NMR time scale. Calix[3]benzofuran 4a exists as two conformers, namely the cone and saddle forms, in a ratio of 83-17 at -50 °C. A series of calix[3]benzofuran derivatives was synthesized by electrophilic aromatic substitutions, such as bromination, formylation and acylation, to investigate the influence of the substituents on the conformations of the calix[3]benzofurans. 1H NMR spectral analyses of the acyl derivatives at room temperature indicated that these macrocycles exist as a mixture of two isomers that are slowly interconverted on the 1H NMR timescale. The conformational isomers of the calix[3]benzofurans and their derivatives obtained from DFT methods (based on the crystal structure analysis results) were used to estimate the total energies of the different conformations.

Original languageEnglish
Pages (from-to)50808-50817
Number of pages10
JournalRSC Advances
Volume6
Issue number56
DOIs
Publication statusPublished - Jan 1 2016

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All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)

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