2-Bicycloheptyl and 7-Norbornyl Cations

Article abstract of DOI:10.1021/jo00222a003

The structure and reactivity of 2-bicyclo<3.2.0>heptyl and 7-norbornyl cations have been probed with the aid of optically active, deuterium-labeled, and methyl-substituted precursors.Bicyclo<3.2.0>heptyl-6,7-d2 and 6-methyl- and 7-methylbicyclo<3.2.0>heptyl substrates rearranged with > 98percent inversion at the migration origin to give anti-7-norbornyl products.Optically active 2-methylbicyclo<3.2.0>heptyl substrates afforded 1-methyl-7-norbornanol of > 98percent ee.Anti-syn leakage is characteristic of 7-norbornyl substrates and may be due to k_Δ,k_c competition.Several carbocations have been shown to undergo "same-side bridge-flipping" (2a<*>2b), leading to partial racemization of the parent system and to structural isomerization of others.Bridge-flipping has not been observed with 2-methylbicyclo<3.2.0> heptyl substrates, owing to stabilization of the carbocation by Me.The product distributions cannot be rationalized in terms of open (classical) ions.Bridged (nonclassical) intermediates provide an internally consistent interpretation of our data.