Intramolecular Pyridinium Oxide Cycloadditions: Systematic Study of Substitution, Diastereoselectivity, and Regioselectivity

Intramolecular pyridinium oxide cycloadditions form complex polycyclic nitrogenous architectures. The diastereoselectivity and regioselectivity of pyridinium oxide cycloadditions was systematically investigated for the first time using complex substrates. Predictably high levels of diastereoselectivity and regioselectivity are observed, which can be attributed to minimization of steric (syn‐pentane) and torsional strain in the products. The reaction is reversible under the reaction conditions, and it is stereospecific with respect to the dipolarophile geometry. The intramolecular cycloaddition of pyridinium oxides was systematically studied. The stereochemical outcome of the reaction results from equatorial positioning of tether substituents. Regiochemistry results from minimization of syn‐pentane interactions and eclipsing interactions. The cycloaddition reaction is stereospecific and reversible.