MEMORY EFFECTS IN MULTIPLE CARBONIUM ION REARRANGEMENTS .V. NUCLEOPHILIC CAPTURE OF AN ASYMMETRIC TRICYCLOOCTYL CATIONIC INTERMEDIATE IN RING EXPANSION OF NORTRICYCLYLCARBINYL SYSTEM

A memory effect is observed in the capture of the first ring-expanded cation in reactions of optically active nortricyclylcarbinyl derivatives. This nucleophilic capture leads to tricyclo[3.2.1.02,7]oct-4-yl derivatives with partial (ca. 30%) survival of the original enantiomeric purity. Configurational correlations show that capture occurs predominantly from the same side as that occupied by the leaving group. The complex series of rearrangements also can be entered from the tricyclo[3.2.1.02,7]oct-6-yl side, with about the same degree of retention of enantiomeric purity. The intermediate responsible for these results cannot be the same as the cation generated in solvolysis of tricyclo[3.2.1.02,7]oct-4-yl derivatives, since that is shown in an accompanying paper to behave quite differently. The nortricyclylcarbinyl and tricyclo[3.2.1.02,4]oct-6-yl products are formed with essentially complete preservation of enantiomeric purity. These results require the postulation of at least two cationic intermediates as precursors of the tricyclo[3.2.1.02,7]oct-4-yl products, and taken together with the detailed product distributions and other evidence, they lead to the formulation of the mechanism of the whole set of interconnected processes. © 1969, American Chemical Society. All rights reserved.