Vertically π‑Expanded
Coumarins: The
Synthesis and Optical Properties
Rashid Nazir
Anton J. Stasyuk
Daniel T. Gryko
10.1021/acs.joc.6b02094.s002
https://acs.figshare.com/articles/journal_contribution/Vertically_Expanded_Coumarins_The_Synthesis_and_Optical_Properties/4206678
A regioselective
synthesis of naphtho[2,1,8-<i>def</i>]coumarins has been
realized through a concise route that involves
the intramolecular Friedel–Crafts reaction of benzo[<i>f</i>]coumarins. Tetracyclic, planar products were prepared
starting from assembly of the suitably substituted coumarin via the
Pechmann reaction of 2-naphthols with acetone-1,3-dicarboxylates,
followed by an intramolecular Friedel–Crafts reaction. In contrast
to earlier report, the main product of the condensation reaction performed
at 130 °C was the corresponding sulfonic acid and not the phenol
itself. The one-pot process afforded the desired phenol in 39% yield.
This reaction has been extended to some naphthalenediols. The model
5-hydroxy-naphtho[2,1,8-<i>def</i>]coumarin was transformed
into corresponding dimer using various pathways including intermolecular
oxidative aromatic coupling. Photophysical studies revealed that 5-hydroxy-naphtho[2,1,8-<i>def</i>]coumarin has the most bathochromically shifted both
absorption and emission among all π-expanded coumarins bearing
one OH functionality. In general, all prepared coumarin-phenols as
well as their hexyl ethers displayed moderate to strong greenish-yellow
fluorescence, except of dimer that emits at 552 nm. The fluorescence
of these dyes was strongly dependent on polarity of the solvent. Computational
studies supported interpretation of optical properties for the selected
compounds.
2016-10-27 00:00:00
regioselective synthesis
Computational studies
one-pot process
552 nm
2- naphthols
Photophysical studies
sulfonic acid
coumarin
OH functionality
hexyl ethers
greenish-yellow fluorescence
Optical Properties
condensation reaction
Pechmann reaction