Abstract
Catalytic hydrogenation (Pd/C) of calix[4]arene afforded derivatives in which one (6a), two distal (7f) or all phenols (11 and 13d) have been hydrogenated. 6a adopts a conformation in which the phenol groups are oriented syn and the cyclohexanol (with an axial OH group) exists in an anti-down arrangement. The cyclohexanol rings of 7f adopt an anti-down/gauche-down conformation and both the equatorial and axial cyclohexanol OH groups are involved in hydrogen bonding. The configuration of the perhydroxanthene subunits of the saturated diether 11 is cis-syn-cis with all C−O bonds located in axial positions of the cyclohexyl rings. In the saturated metacyclophane 13d pairs of methine hydrogens at the four rings are arranged alternately above and below the mean macrocyclic plane. Calculations with the MM3 program indicate that 6a and 13d are the lowest energy isomers.
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