Stable carbocations. Part 16. Properties of 2-substituted exo-5,6-trimethylenenorbornan-2-ylium ions

Abstract

In formic acid solution, the 2-methyl-exo-5,6-trimethylenenorbornan-2-ylium ion gives products resulting from Wagner–Meerwein rearrangement, 3,2-hydride shift, and cation–alkene coupling. Under similar conditions, the 2-phenyl analogue also gives dimeric coupling products, whereas the 2-ferrocenyl analogue is stable. The last-mentioned cation has been obtained in stereoisomeric forms which interconvert in trifluoroacetic acid solution.