A practical pinacol coupling of diaryl ketones is developed by employing a stable diboron reagent and pyridine Lewis base catalyst. The operationally simple process affords the desired diols with excellent efficiency in up to 99% yield within 1 hour.
Natural
light-harvesting complexes (LHCs) absorb a broad spectrum
of sunlight using a collection of photosynthetic pigments whose spatial
arrangement is controlled by a protein matrix and exhibit efficient
energy transfer. We constructed a novel light-harvesting protein mimic,
which absorbs light in the UV to visible region (280–700 nm)
by displaying flavone and porphyrin on a peptoid helix. First, an
efficient synthesis of 4′-derivatized 7-methoxyflavone (7-MF, 3 and 4) was developed. The flavone–porphyrin–peptoid
conjugate (FPPC) was then prepared via Miyaura borylation on a resin-bound
peptoid followed by Suzuki coupling between the peptoid and pigment.
Circular dichroism spectroscopy indicated that the FPPC underwent
helix-to-loop conversion of the peptoid scaffold upon changing the
solvent conditions. A distinct intramolecular energy transfer was
observed from 7-MF to porphyrin with greater efficiency in the helix
than that in the loop conformation of the peptoid, whereas no clear
evidence of energy transfer was obtained for unstructured FPPC. We
thus demonstrate the value of the helical peptoid, which provided
a controlled orientation for 7-MF and porphyrin and modulated the
energy transfer efficiency via conformational switching. Our work
provides a way to construct a sophisticated LHC mimic with enhanced
coverage of the solar spectrum and controllable energy transfer efficiency.
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