Theoretical Investigation On BF₃·OEt₂-Catalyzed Tandem Benzannulation/Friedel–Crafts Reaction Of 2-Alkynylaniline And 2-Alkynylbenzaldehyde Delivering Highly π-Extended Dihydrobenzo[a]indenocarbazole

Nan Lu*, Chengxia Miao

College of Chemistry and Material Science, Shandong Agricultural University, Taian 271018, (P. R. CHINA)

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ABSTRACT – DOI: https://dx.doi.org/10.47204/EMSR.6.2.2024.107-114

Our DFT calculations provide the first theoretical investigation on BF₃·OEt₂-facilitated benzannulation/Friedel–Crafts reaction of 2-(phenylethynyl)aniline with 2-(phenylethynyl)benzaldehyde. Imine is formed mediated by BF₃·OEt₂ via initial two steps. The subsequent nucleophilic attack from alkyne group of 2-(phenylethynyl)aniline forms the first alkenyl carbocation and five-membered ring continuously activated by BF₃·OEt₂. With additional proton, the second alkenyl carbocation is given by attack from alkyne group of 2-(phenylethynyl)benzaldehyde together with novel six-membered ring. Then intramolecular Friedel–Crafts reaction and aromatization give rise to the second five-membered ring. The product dihydrobenzo[a]indeno[2,1-c]carbazole is finally obtained via 1,5-H shift, which is determined to be rate-limiting owing to the tension resulting from great structure bending required by long-distance shifting. The positive solvation effect is suggested by decreased absolute and activation energies in solution compared with in gas. These results are supported by Multiwfn analysis on FMO composition of specific TSs, and MBO value of vital bonding, breaking.