Synthesis of Substituted 2‑Arylindanes from <i>E</i>‑(2-Stilbenyl)methanols via Lewis Acid-Mediated
Cyclization and Nucleophililc Transfer from Trialkylsilyl Reagents
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Abstract
A preparative method for the synthesis
of functionalized 2-arylindanes
has been developed via the Lewis acid-mediated ring closure of stilbenyl
methanols followed by nucleophilic transfer from trialkylsilyl reagents.
The reactions gave the corresponding products in moderate to high
yields and diastereoselectivity. The solvent as well as the nucleophile
played an important role in determining the type(s) of product arising
either from nucleophilic addition (indanes) or loss of a proton β
to the indanyl-type carbocations (indenes). Electron-donating groups
on the fused aromatic ring (Y and Z = OMe) or the presence of electron-withdrawing
groups (NO<sub>2</sub>) on the nonfused Ar ring facilitate the cyclization.
In contrast, the presence of electron-donating groups (OMe) on the
nonfused Ar ring impedes the process. In the case of Cl on the nonfused
Ar ring, temperature modulates the resonance versus inductive field
effects on the overall reaction pathways involving cyclization to
form the indanyl-type cation. Quantum chemical calculations supported
the intermediacy of the carbocation species and the transfer of hydride
from triethylsilane (Nu = H) to the indanyl-type cations to form the <i>trans</i>-1,2-disubstituted indane as the single diastereomer
product