The reaction described in the previous post (below) is an unusual example of nucleophilic attack at an sp2-carbon centre, reportedly resulting in inversion of configuration. One can break it down to a sequence of up to eight individual steps, which makes teaching it far easier. But how real is that sequence?
- T.C. Clarke, and R.G. Bergman, "Olefinic cyclization at a vinyl cation center. Inversion preference for intramolecular nucleophilic substitution by a double bond", J. Am. Chem. Soc., vol. 94, pp. 3627-3629, 1972. http://dx.doi.org/10.1021/ja00765a062