Protonation-Gated Strain-Release Generation of Amino- o -quinodimethanes

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.