Atropisomerism in Tertiary Biaryl 2-Amides: A Study of Ar-CO and Ar-Ar′ Rotational Barriers
Lorentzen, Marianne; Kalvet, Indrek; Sauriol, Françoise; Rantanen, Toni; Jørgensen, Kåre Bredeli; Snieckus, Victor (2017). Atropisomerism in Tertiary Biaryl 2-Amides: A Study of Ar-CO and Ar-Ar′ Rotational Barriers. The Journal of Organic Chemistry, 82, 7300−7308. DOI: 10.1021/acs.joc.7b00890.
Lorentzen, Marianne; Kalvet, Indrek; Sauriol, Françoise; Rantanen, Toni; Jørgensen, Kåre Bredeli; Snieckus, Victor
The Journal of Organic Chemistry
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A rotational barrier study was performed on eight tertiary biaryl 2-amides using variable-temperature (VT) NMR and exchange (EXSY) spectroscopy experiments. Seven out of the eight 2-amido-2′-methylbiphenyls with additional 3- and 6-substitution patterns (1–7) were found to have approximately similar rotational barriers (ΔG⧧Tc = 56.5–67.5 kJ/mol). However, for both 3- and 6-substitution (8), the rotational barrier was found to be significantly higher (ΔG⧧ = 102.6–103.8 kJ/mol). Computational studies performed on all eight compounds gave results in good agreement with the experimental rotational barriers. A transition state in which atropisomerism occurs by a cooperative rotation of the Ar–CO and Ar–Ar′ bonds depending on substituent location is proposed.