Janus Face All-cis 1,2,4,5-tetrakis(trifluoromethyl)- and All-cis 1,2,3,4,5,6-hexakis(trifluoromethyl)- Cyclohexanes |
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Authors: | Cihang Yu Dr Agnes Kütt Prof?Dr Gerd-Volker Röschenthaler Dr Tomas Lebl Dr David B Cordes Prof?Dr Alexandra M Z Slawin Prof?Dr Michael Bühl Prof?Dr David O'Hagan |
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Institution: | 1. School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY16 9ST UK;2. Department of Life Sciences and Chemistry, Jacobs University Bremen, gGmbH, P.O. Box 750 561, 28725 Bremen, Germany |
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Abstract: | We report the synthesis of all-cis 1,2,4,5-tetrakis (trifluoromethyl)- and all-cis 1,2,3,4,5,6-hexakis (trifluoromethyl)- cyclohexanes by direct hydrogenation of precursor tetrakis- or hexakis- (trifluoromethyl)benzenes. The resultant cyclohexanes have a stereochemistry such that all the CF3 groups are on the same face of the cyclohexyl ring. All-cis 1,2,3,4,5,6-hexakis(trifluoromethyl)cyclohexane is the most sterically demanding of the all-cis hexakis substituted cyclohexanes prepared to date, with a barrier (ΔG) to ring inversion calculated at 27 kcal mol?1. The X-ray structure of all-cis 1,2,3,4,5,6-hexakis(trifluoromethyl)cyclohexane displays a flattened chair conformation and the electrostatic profile of this compound reveals a large diffuse negative density on the fluorine face and a focused positive density on the hydrogen face. The electropositive hydrogen face can co-ordinate chloride (K≈103) and to a lesser extent fluoride and iodide ions. Dehydrofluorination promoted decomposition occurs with fluoride ion acting as a base. |
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Keywords: | aryl hydrogenation cyclohexanes Janus face triaxial orientations trifluoromethyl groups |
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