Stereodynamics of 9,11-diphenyl-10-azatetracyclo(6.3.0.0.(super 4,11)0.(super 5,9))undecanes. Highly restricted nitrogen inversion and isolated phenyl rotation. X-ray crystallographic, dynamic NMR, and molecular mechanics studies

The slowing of inversion at nitrogen and the slowing of isolated bridgehead phenyl rotation disrupt the 1H NMR spectra of 10-benzyl-9,11-diphenyl-10-azatetracyclo(6.3.0.0.(super 4,11)0.(super 5,9))undecane and 10-methyl-9,11-diphenyl-10-azatetracyclo(6.3.0.0.(super 4,11)0.(super 5,9))undecane. Molecular mechanics calculations indicate that the close passage of an o-phenyl proton and a methyl (or benzylmethylene) proton in the transition state give rise to the high phenyl rotation barriers.