A reader asked me about the mechanism of the reaction of 2-picoline N-oxide with acetic anhydride to give 2-acetoxymethylpyridine (the Boekelheide Rearrangement[1]). He wrote ” I don’t understand why the system should prefer to go via fragmentation-recombination (… the evidence being that oxygen labelling shows scrambling) when there is an easy concerted pathway available (… a [3,3]sigmatropic shift). Furthermore, is it possible for two pathways to co-exist?” Here is how computation might enlighten us.
References
- A. Massaro, A. Mordini, A. Mingardi, J. Klein, and D. Andreotti, "A New Sequential Intramolecular Cyclization Based on the Boekelheide Rearrangement", European Journal of Organic Chemistry, vol. 2011, pp. 271-279, 2010. http://dx.doi.org/10.1002/ejoc.201000936