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Protonation-Gated Strain-Release Generation of Amino-o-quinodimethanes
Domenic Kronenberg1, Asja A Kroeger2, Jiao Yu J Wang2
1Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory2601, Australia.
Abstract:
Free amino-benzocyclobutenes remain underexplored as precursors to amino-ortho-quinodimethanes, and the influence of the protonation state on their electrocyclic reactivity is unknown. Here, we show that amino-benzocyclobutenes function as protonation-gated, strain-release precursors to highly reactive amino-o-quinodimethanes. Protonation toggles electrocyclic ring opening off and on by removing or restoring n(N) → σ*(C-C) stabilization, shifting the activation barrier by >50 kJ mol-1. Kinetic measurements define a >103-fold reactivity window, while computed barriers reproduce experimental half-life trends quantitatively. No amino-o-quinodimethane intermediate is detected, consistent with [4 + 2] trapping outcompeting its accumulation following electrocyclic ring opening. This acid-base switch enables the use of stable ammonium precursors and on-demand generation of transient intermediates under mild conditions, providing practical protonation-state control over the storage and activation of amino-BCB precursors.
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