AlCl(3)-Catalyzed Cascade Reactions of 1,2,3-Trimethoxybenzene and Adipoyl Chloride: Spectroscopic Investigations and Density Functional Theory Studies

[Image: see text] The reaction of 1,2,3-trimethoxybenzene with adipoyl chloride in the presence of AlCl(3) gave two isomeric cyclopentene derivatives, 1,6-bis(2,3,4-trimethoxyphenyl)hexane-1,6-dione, and two demethylation products of aryl methyl ethers. The cyclopentene derivatives including unconjugated or conjugated enones are products formed in a cascade reaction resulting from first the Friedel–Crafts acylation reaction and then aldol condensation. All compounds were optimized by density functional theory calculated using two functional levels, B3LYP and M06-2X, with the 6-311+G(d,p) basis set. The structural properties were established, natural bond orbital analysis of donor–acceptor interactions was carried out, and charges on the atoms and quantum chemical reactivity identifiers were determined to compare the strength of the intramolecular hydrogen bonds formed and their stabilities. To compare the experimental (1)H and (13)C NMR chemical shifts with the calculated values, NMR chemical shift calculations were carried out using the gauge-invariant atomic orbital method.