Unimolecular Variant of the Fluorescence Turn-On Oxidative Coupling of Catecholamines with Resorcinols

Reported herein is a unimolecular variant of the fluorescence turn-on oxidative coupling of catecholamines with resorcinols (FluoResCat) based on the easily accessible conjugate 4-(2-((2,4-dihydroxybenzyl)amino)ethyl)benzene-1,2-diol (1). The process involves an alkali-activatable sequence of autoxidation and intramolecular cyclization steps with loss of carbon, leading to a fluorescent methanobenzofuroazocinone product identical to that obtained from the oxidative coupling of dopamine with resorcinol. A mechanistic route for this unexpected reaction, mimicking the synthesis of the natural fluorophore matlaline, would involve highly constrained polycyclic spiro intermediates (liquid chromatography-mass spectrometry analysis of intermediates, model reactions, and density functional theory calculations). Emission turn-on from 1 in response to oxygen, superoxide-generating systems, or gaseous ammonia/volatile amines may be of interest for sensing applications, for example, in smart packaging.