Treatment of α-alkylcinnamaldehydes with orthoesters, alcohols, or thiols in the presence of BF3·OEt2 induces an intramolecular electrophilic aromatic substitution reaction to afford 1-alkoxy-2-alkylindenes. The reaction mechanisms of the indene formation have been elucidated on the basis of the reaction behaviors of β-deuterated α-methylcinnamaldehyde and the NMR studies of the reaction mixture. The transformation process involves successive reactions, i.e., alkoxylation of the carbonyl carbon of α-alkylcinnamaldehydes to form acetals, elimination of alkoxide from the acetals to give alkoxycarbenium ion and γ-alkoxyallyl cation, and intramolecular electrophilic arylation to afford the indene ring structure. © 2006 Elsevier Ltd. All rights reserved.
Jobashi, T., Kawai, A., Kawai, S., Maeyama, K., Oike, H., Yoshida, Y., & Yonezawa, N. (2006). Intramolecular electrophilic aromatic substitution of α-alkylcinnamaldehydes affording 1-alkoxy-2-alkylindenes. Tetrahedron, 62(24), 5717–5724. https://doi.org/10.1016/j.tet.2006.03.092