5 years ago

Atropisomerism in Tertiary Biaryl 2-Amides: A Study of Ar–CO and Ar–Ar′ Rotational Barriers

Atropisomerism in Tertiary Biaryl 2-Amides: A Study of Ar–CO and Ar–Ar′ Rotational Barriers
Victor Snieckus, Kåre B. Jørgensen, Toni Rantanen, Francoise Sauriol, Marianne Lorentzen, Indrek Kalvet
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 (17) were found to have approximately similar rotational barriers (ΔGTc = 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.

Publisher URL: http://dx.doi.org/10.1021/acs.joc.7b00890

DOI: 10.1021/acs.joc.7b00890

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