ja502644e_si_003.cif (22.72 kB)
Thiophene-Fused Borepins As Directly Functionalizable Boron-Containing π‑Electron Systems
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posted on 2014-05-14, 00:00 authored by David
R. Levine, Maxime A. Siegler, John D. TovarSynthetic
protocols were developed for the gram-scale preparation
of two isomeric dithienoborepins (DTBs), boron-containing polycyclic
aromatics featuring the fusion of borepin and thiophene rings. DTBs
exhibit reversible cathodic electrochemistry and boron-centered Lewis
acidity in addition to enhanced electronic delocalization relative
to benzo-fused analogues. Boron’s precise position within the
conjugation pathway of DTBs significantly affected electronic structure,
most clearly demonstrated by the variation in spectroscopic responses
of each isomer to fluoride ion binding. In addition to excellent stability
in the presence of air and moisture, DTBs could also be subjected
to electrophilic aromatic substitution and metalation chemistry, the
latter enabling the direct, regiospecific functionalization of the
unsubstituted thiophene rings. Subsequent tuning of molecular properties
was achieved through installation of donor and acceptor π-substituents,
leading to compounds featuring multistep electrochemical reductions
and polarizable electronic structures. As rare examples of directly
functionalizable, π-conjugated, boron-containing polycyclic
aromatics, DTBs are promising building blocks for the next generation
of organoboron π-electron materials whose development will demand
broad scope for molecular diversification in addition to chemical
robustness.
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Keywords
metalation chemistrycathodic electrochemistryisomeric dithienoborepinsfluoride ion bindingpolycyclicregiospecific functionalizationchemical robustnessbuilding blocksthiophene ringsconjugation pathwayspectroscopic responsesmultistep electrochemical reductionsunsubstituted thiophene ringsaromaticDTBs exhibit
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