Wagner-Meerwein rearrangement of a [3.3.3]- to a [4.3.3]propellane: deuterium tracer and conformational analysis.

Formation of (-)-[4.3.3]propellane 4 from (-)-14-hydroxymodhephene (2) proceeds through a Wagner-Meerwein rearrangement via C3--C4 bond-shift to give a stable intermediate, dimethylcyclohexadienyl cation A, which undergoes deprotonation. Herein, this mechanism was investigated by using a deuterium labeled substrate at the C-14 methylene group of (-)-2, which was incorporated into the C-4 position of (-)-[4.3.3]propellane 4. The stereostructure of (-)-4 was investigated by applying a combination of NMR experimental and theoretical approaches.