Birch Reduction of Hexaphenyl‐ and Pentaphenylbenzene and an X‐ray Crystallography and NMR Spectroscopy Study of cis‐ and epi‐1,2,3,4,5,6‐Hexaphenylcyclohexane and of 2,3,5,6‐Tetraphenyl‐1,1′‐bicyclohexylidene: Cannizzaro's Conundrum Revisited

The Birch reduction of hexaphenylbenzene yields two isomers of 1,2,3,4,5,6-hexaphenylcyclohexane. The X-ray crystal structure of the all-cis isomer, 1, reveals that the severe steric crowding among the three axial phenyls is alleviated by a marked splaying out of those three aryl substituents relative to the positioning in a conventional chair structure. A second product, 2, was identified crystallographically and by NMR spectroscopy as the …