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

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

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.

Citation

Islam, M. M., Akther, T., Ikejiri, Y., Matsumoto, T., Tanaka, J., Rahman, S., …Yamato, T. (in press). Synthesis, structural properties, electrophilic substitution reactions and DFT computational studies of calix[3]benzofurans. RSC advances, 6(56), 50808-50817. https://doi.org/10.1039/c6ra06219a

• Journal Article Type: Article
• Acceptance Date: May 16, 2016
• Online Publication Date: May 18, 2016
• Deposit Date: Jun 21, 2016
• Publicly Available Date: Jun 21, 2016
• Journal: RSC advances
• Print ISSN: 2046-2069
• Electronic ISSN: 2046-2069
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 6
• Issue: 56
• Pages: 50808-50817
• DOI: https://doi.org/10.1039/c6ra06219a
• Keywords: Calix[3]benzofurans
• Public URL: https://hull-repository.worktribe.com/output/440002
• Publisher URL: http://pubs.rsc.org/en/content/articlelanding/2016/ra/c6ra06219a#!divAbstract
• Additional Information: : This document is Similarity Check deposited; : Supplementary Information; : Crystal Structure Data; : The Royal Society of Chemistry has an exclusive publication licence for this journal; : Single-blind; : Received 9 March 2016; Accepted 16 May 2016; Accepted Manuscript published 18 May 2016; Version of Record published 24 May 2016