Synthesis of substituted 2-arylindanes from E-(2-stilbenyl)methanols via Lewis acid-mediated cyclization and nucleophililc transfer from trialkylsilyl reagents.

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 (NO2) 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 trans-1,2-disubstituted indane as the single diastereomer product.