Synthesis of 1‑Silabenzo[d,e]isochromanes via Electrophilic Aromatic Substitution of Aldehydes Activated by Silylium Ion

• Published in: ACS omega Vol. 7; no. 6; pp. 5166 - 5175
• Main Authors: Arii, Hidekazu, Nakao, Kenichi, Masuda, Hideki, Kawashima, Takayuki
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.02.2022
• ISSN: 2470-1343; 2470-1343
• DOI: 10.1021/acsomega.1c06228

A strong Lewis acid silylium ion was utilized for dehydrogenative annulation between dialkyl­(1-naphthyl)­silanes 1 and aldehydes 2. Silane 1a was reacted with [Ph3C]­[B­(C6F5)4] in the presence of 2,6-di-tert-butyl-4-methylpyridine and aldehydes 2 to afford the annulation product, 1-silabenzo­[d,e]­isochromanes 3, in moderate isolated yields. The annulation occurred only at the 8-position on the 1-naphthyl group. The silylium ion-promoted hydrosilylation proceeded competitively to afford silyl ethers 4 via the same intermediates, silylcarboxonium ions, in the dehydrogenative annulation. The ratio of 3 and 4 was affected by solvents and the electronic properties of aromatic aldehydes; for example, the use of less polar solvents and that of benzaldehydes with an electron-withdrawing group at the para-position predominantly yielded 3. This annulation reaction was applicable to aldehydes bearing a heteroaromatic group and aliphatic alkyl groups. Judging from these results, both the formation of silylcarboxonium ions by in situ-generated silylium ions and the electrophilic aromatic substitution are important for this annulation reaction.