What is "mechanistic duality"? I am doing a general overview of different kinds of dualities present in science. I am quite well versed with the dualities in physics and mathematics. I was searching for dualities in chemistry, biology and other sciences. In that process, I encountered "mechanistic duality" in chemistry. For instance, see [1] and [2].

But I am not able to find a good introduction or description about "mechanisitic duality". It would also be nice if someone can briefly explain what this duality mean. Does someone have clue about its history (who coined it first and for what purpose)? Also, please point me to relevant book/paper which discuss this.




Denmark, S. E.; Su, X.; Nishigaichi, Y. The Chemistry of Trichlorosilyl Enolates. 6. Mechanistic Duality in the Lewis Base-Catalyzed Aldol Addition Reaction. J. Am. Chem. Soc. 1998, 120 (49), 12990–12991. DOI: 10.1021/ja982993v.
Ross, S. P.; Baire, B.; Hoye, T. R. Mechanistic Duality in Tertiary Amine Additions to Thermally Generated Hexadehydro-Diels–Alder Benzynes. Org. Lett. 2017, 19 (20), 5705–5708. DOI: 10.1021/acs.orglett.7b02888.
This just means that the same type of reaction may proceed by two different mechanisms depending on the exact chemical being used. It's not a particularly widely used term (it is not a "standard" phrase such as wave-particle duality) and there are many other ways of saying the same thing ("divergence", "pathway", etc.).

As an extremely simple example, alkyl bromides can react with nucleophiles via either an SN1 or SN2 pathway, depending on the degree of substitution of the carbon bonded to bromine. This is an example of how a different substrate may follow a different mechanism, although the end result is the same (replacement of Br with the nucleophile).

The papers you cited are just slightly more sophisticated examples of the same concept.