Towards Tailored Metastability: Exploring Oxanorbornene Chemical Space for Structure-Stability Relationships with Atypical Furan Diels-Alder Adducts

The furan Diels-Alder (DA) cycloaddition is a highly versatile synthetic tool in the design of smart and biobased molecular and macromolecular applications. As a prototypical example of reversible reactions, it is ideally suited for exploring intrinsic chemical metastability, i.e. how to introduce a degree of non-persistence, tailored to an envisaged application, into the molecular architecture. While the (furan) DA field has seen tremendous progress since its emergence nearly a century ago, its scope remains largely limited to combinations of activated addends. Here, we explore previously inaccessible areas of the oxanorbornene chemical space by investigating the properties of atypical furan DA (formal) adducts and demonstrate that stability against cycloreversion, i.e. their metastability, can be altered over six orders of magnitude. The emerging structure-stability relationships provide new insights into the delicate kinetics/thermodynamics interplay of furan [4+2] cycloadditions, paving the way for the rational design of applications that exploit either direction of the DA equilibrium. Such tailored non-persistence can be exploited as a strategy for a sustainable materials transition.