Rapid access to C₃- and C_s-symmetric AAT organogelators via ring opening of a common benzotrifuranone precursor

Abstract

Presented is a rapid and general approach to functionalised 1-aza-adamantanetrione (AAT) donor-σ-acceptor molecules from a phloroglucinol-derived trilactone, benzotrifuranone (BTF). Ten C ₃-symmetric AATs bearing diverse aryl amide substituents are accessed in two synthetic steps: (1) the exhaustive ring opening of BTF with aromatic amine nucleophiles (performed in up to 91% yield) and (2) cyclisation with hexamethylenetetramine (performed in up to 75% yield). Additionally, stepwise ring opening of BTF allows synthesis of phloroglucinol intermediates with two unique aryl amide substituents and ultimately C _s-symmetric AATs. Of the novel AATs prepared, three (including the C _s-symmetric hybrid) are effective gelators of chlorinated solvents (critical gelation concentration (CGC) = 0.2–0.4 wt%) and one, with naphthyl substituents, forms translucent gels from aromatic solvents (CGC∼0.3 wt%). The combination of AATs with moderately electron-poor and electron-rich aromatic substituents results in functional complementarity and gelation at concentrations below what is required for the individual components. Electron microscopy of the gel morphologies shows high aspect ratio fibres underlying the gel network superstructures in most cases. Polarised optical microscopy has allowed imaging of representative native organogel phases, and reveals striking morphology differences between gels that also share different optical and/or thermal stability properties.

Keywords:

• donor–acceptor molecules
• gels
• self-assembly
• symmetry
• through-bond interactions

Acknowledgements

This work was financially supported by the National Science Foundation CAREER programme (CHE-0548003). MBB and YL were supported by a University of Florida (UF) Alumni Graduate Fellowship and CLAS Dissertation Fellowship, respectively. CJM would like to thank the HHMI-UF Science for Life Program for an Undergraduate Research Award and the Barry M. Goldwater Scholarship and Excellence in Education Program for funding. We are grateful to Dr Kerry Siebein and the Major Analytical Instrumentation Center (MAIC), Department of Materials Science and Engineering, University of Florida, for SEM and TEM imaging. The authors would also like to thank the personnel in Mass Spectrometry Services, Department of Chemistry, University of Florida, for diligent characterisation of the molecules presented in this paper.

Notes

^†Dedicated to the memory of Prof. Dmitry M. Rudkevich.