Nickel catalyzed synthesis of 4,4′-bichromenes/4,4′-bithiochromenes and their Atropisomerism

Somasundaram Muthuramalingam, Jai Anand Garg, R. Karthick, Thomas Fox, Olivier Blacque, Koushik Venkatesan, Saiganesh Ramanathan, Senthamaraikannan Kabilan*, K. K. Balasubramanian

*Corresponding author for this work

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Abstract

Axially chiral molecules have established undisputed importance in both medicinal chemistry and enantiomeric catalysis. The size, shape and hybridization of the substituent adjacent to the rotational axis greatly dictate atropisomerism. Herein, we examined the tropoisomeric behavior of 4,4′-bichromenes and 4,4′-bithiochromenes derivatives that were synthesized by a nickel catalyzed reductive homocoupling strategy. The as-synthesized 3,3′-disubstituted 4,4′-bichromenes displayed atropisomerism, as evidenced by chiral stationary phase HPLC, electronic circular dichroism and single crystal XRD studies. Insights into the torsional barrier about the internuclear axis in 4,4′-bichromenes were gained both experimentally and theoretically (DFT studies). The lower activation energy barrier (Ea) of approximately 12 kcal mol-1 as compared to that of fully aromatic 1,1′-binapthyl explains the conformationally unstable nature of 3,3′-unsubstituted 4,4′-bichromenes at room temperature.

Original languageEnglish
Pages (from-to)134-139
Number of pages6
JournalOrganic Chemistry Frontiers
Volume6
Issue number1
DOIs
Publication statusPublished - 7 Jan 2019

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Muthuramalingam, S., Garg, J. A., Karthick, R., Fox, T., Blacque, O., Venkatesan, K., ... Balasubramanian, K. K. (2019). Nickel catalyzed synthesis of 4,4′-bichromenes/4,4′-bithiochromenes and their Atropisomerism. Organic Chemistry Frontiers, 6(1), 134-139. https://doi.org/10.1039/c8qo00820e