Intramolecular (4 + 3) cycloadditions of oxidopyridinium ions : towards daphnicyclidin A

[EMBARGOED UNTIL 5/1/2024] N-alkylation of alkyl 5-hydroxynicotinates with electrophiles containing diene functionality produces salts , which can undergo intramolecular (4 + 3) cycloaddition reactions when heated in the presence of a base. Initially, a three-carbon tether was used to connect the pyridinium ion and the diene. However, synthesizing related compounds with a two-carbon tether proved to be much more challenging. To overcome this obstacle, a dimethylenecyclopentane was successfully synthesized, and a sulfur dioxide protection was introduced. Using these compounds, the researchers were able to successfully achieve the cycloaddition reaction, leading directly to the ABC tricyclic ring system, as well as the ABCE tetracyclic ring system found in the alkaloid daphnicyclidin A.Includes bibliographical references