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Mechanical Manipulation of Chemical Reactions: Reactivity Switching of Bergman Cyclizations
journal contribution
posted on 2015-12-17, 00:55 authored by Martin Krupička, Wolfram Sander, Dominik MarxPhotoswitches incorporated into molecular
frameworks have been
used since a long time to trigger chemical processes on demand. Here,
it is shown how mechanophores can be used as switches in order to
drastically change the reactivity of a neighboring functional group
as a function of external stress. The reactivities of cyclic enediynes,
which are highly toxic agents when undergoing Bergman cyclization,
roughly correlate with the distance between the bond-forming carbons
in many cases. It is demonstrated how this distance, and thus enediyne
reactivity, can be tuned upon applying mechanical stress. Depending
on suitable substitution patterns, chemically inert species can be
turned into highly reactive ones and vice versa, thus extending the
concept of photoswitching to mechanoswitching. Moreover, depending
on the derivative, it is found that C1–C5 cyclization becomes energetically preferred over the Bergman (C1–C6) pathway at nano-Newton forces, thus
leading to a force-induced switch in selectivity in such cases.