August 2023

Acid-catalyzed [4+1]-dearomatization spiroannulation reactions of electron-rich hydroquinone and naphthol derivatives were demonstrated as convenient methods to access spirocyclic cyclohexadienone derivatives. The Lewis acid Bi(OTf)3 exhibited the best catalytic performance when a 1,2-dialkynylbenzene was used as the electrophile for the spiroannulation, whereas the Brønsted acid benzene-1,2-disulfonic acid was the best catalyst when 2-ethynylbenzylic esters were used as electrophiles. Most of the reaction conditions are mild, efficient, and simple to operate.

Numerous strategies for enhancing the reactivity and properties of p-block elements have been devised in the past decades. This Account discusses our approaches by distinct ligand control on p-block elements in their normal (group) oxidation states. Catecholato ligands on silicon, germanium, or phosphorus produce a range of rewarding properties. Substantial electron withdrawal paired with structural constraint effects (influence of deformation energy) impart Lewis superacidity to these abundant elements. The ease of synthesis of such species facilitates screening in catalysis, promising a range of applications by powerful bond activation. Low-barrier Si–O/Si–O bond metathesis provides the most abundant bond in our Earth’s crust, with adaptive features under mild conditions, and establishes a new branch of constitutional dynamic chemistry. The redox-active character of catecholates grants access to novel compounds with tunable open-shell features. Overall, p-block catecholates offer unique opportunities due to their versatile features that will enrich the chemistry of the main-group elements.1 Introduction2 Halogenated Catecholates at Silicon Cause Substantial Lewis Acidity3 Constitutional Dynamics Cause a Structural Mystery4 Strong Silicon Lewis Acids Allow the Exploration of Uncharted Structures, Bond Activations, and Catalysis5 The Catechol Approach on Other Elements: Germanium and Phosphorus6 Catechols Are Redox Active: Also at Silicon7 Conclusion