1 research outputs found
Synthesis of 1,2-Bis(2-aryl‑1<i>H</i>‑indol-3-yl)ethynes via 5-<i>exo</i>-Digonal Double Cyclization Reactions of 1,4-Bis(2-isocyanophenyl)buta-1,3-diyne with Aryl Grignard Reagents
New
Ï€-conjugated 1,2-bisÂ(2-aryl-1<i>H</i>-indol-3-yl)Âethynes <b>1a</b>–<b>j</b> having various substituents on the
two aryl groups were efficiently synthesized via unusual 5-<i>exo</i>-digonal double isocyanide-acetylene cyclization reactions
of 1,4-bisÂ(2-isocyanophenyl)Âbuta-1,3-diyne <b>3</b> and aryl
Grignard reagents (R-MgBr, R = C<sub>6</sub>H<sub>5</sub> (<b>1a</b>), 4-H<sub>3</sub>CC<sub>6</sub>H<sub>4</sub> (<b>1b</b>),
2-H<sub>3</sub>CC<sub>6</sub>H<sub>4</sub> (<b>1c</b>), 3-MeOC<sub>6</sub>H<sub>4</sub> (<b>1d</b>), 3-(CH<sub>3</sub>)<sub>2</sub>NC<sub>6</sub>H<sub>4</sub> (<b>1e</b>), 4-F<sub>3</sub>CC<sub>6</sub>H<sub>4</sub> (<b>1f</b>), 4-FC<sub>6</sub>H<sub>4</sub> (<b>1g</b>), 3-FC<sub>6</sub>H<sub>4</sub> (<b>1h</b>), 4-PhOC<sub>6</sub>H<sub>4</sub> (<b>1i</b>), and 2-Naph
(<b>1j</b>)) in 19–85% yields. The UV–vis spectra
were rationalized in detail using time-dependent DFT and single point
calculations. The fluorescence emission peaks for <b>1a</b>–<b>j</b> were observed at around 450 nm. Especially for <b>1f</b> and <b>1j</b>, those spectra displayed broad emission bands
and relatively large Stokes shifts (3977–4503 cm<sup>–1</sup>), indicating the contribution of an intramolecular charge transfer.
The absolute quantum yields (0.50–0.62) of <b>1a</b>–<b>j</b> were higher than those of parent <b>8</b> (0.19) and
2-phenyl-1<i>H</i>-indole (0.11). The electrochemical features
for <b>1a</b>–<b>j</b> were investigated by cyclic
voltammetry. The frontier molecular orbital levels for <b>1a</b>–<b>j</b> were estimated based on the combination of
oxidation potentials, UV–vis, and DFT calculated data. The
structural property of 1,2-bisÂ(2-phenyl-1<i>H</i>-indol-3-yl)Âethyne <b>1a</b> was characterized by several spectroscopic methods and
finally determined by X-ray analysis of a single crystal of <b>1a</b> recrystallized from ethyl acetate. The structural features
of <b>1a</b>–<b>j</b> were also supported by DFT
calculations