Hydrogenation of [5]- and [6]Metacyclophane: Reactivity and Thermochemistry

Abstract

The course of the hydrogenation of [5]- and [6]metacyclophane (1 b and 1 c) and their thermochemistry is described. Both compounds are hydrogenated rapidly (within 10 s) to furnish the bridgehead olefins 13 b and 12 c. The accompanying hydrogenation enthalpies are −220 and −141 kJ mol−1, respectively. Strain energies (SE) and olefinic strains (OS) of a number of bridgehead olefins have been evaluated by DFT calculations; it was concluded that 13 b belongs to the class of hyperstable olefins which correlates nicely with its reluctance to undergo hydrogenation. By combining experimental hydrogenation enthalpies and DFT calculations, SE of 187 and 121 kJ mol−1 were derived for 1 b and 1 c.