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

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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.

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

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Publication details

The article was received on 03 Aug 2018, accepted on 20 Nov 2018 and first published on 22 Nov 2018


Article type: Research Article
DOI: 10.1039/C8QO00820E
Citation: Org. Chem. Front., 2019, Advance Article
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    Nickel catalyzed synthesis of 4,4′-bichromenes/4,4′-bithiochromenes and their Atropisomerism

    S. Muthuramalingam, J. A. Garg, R. Karthick, T. Fox, O. Blacque, K. Venkatesan, S. Ramanathan, S. Kabilan and K. K. Balasubramanian, Org. Chem. Front., 2019, Advance Article , DOI: 10.1039/C8QO00820E

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