The bicyclo[2.2.2]octyl carbene system as a probe for migratory aptitudes of hydrogen to carbenic centers

A series of tosylhydrazone derivatives of exo-6-substituted bicylo[2.2.2]oc tan-2-ones have been prepared. Thermal decomposition of the sodium salts of these tosylhydrazones gives carbene-derived products from 1,3-migration of either the C6 hydrogen (perturbed)or the C7 hydrogen (unperturbed), along with smaller amounts of alkenes derived from 1,2-hydrogen migration. The ex o-6-substituent strongly activates 1,3-hydrogen migration in the case of Si Me3 and weakly activates it in the case of CH3 substitution. Thiomethoxy an d carbomethoxy are weakly deactivating, while cyano and methoxy groups are strongly deactivating. B3LYP/6-31G* calculations on these substituted carbe nes and transition states ate in qualitative agreement with the ease of 1,3 -hydrogen migration of perturbed vs unperturbed hydrogen. These-experimenta l results and computational studies suggest carbene stabilization due to th e exo-6-silyl group. They also suggest a reactant-like transition state for 1,3-hydrogen migration in; which the inductive effect influences ease of m igration. In the case of the exo-6-methoxy group, the inductive effect over whelms any potential resonance-stabilizing effects.