Insights into the Formation of Symmetrical Trimers of Dialkylated Ketenes Starting from Acid Chloride Precursors

摘要

Application of known dialkyl ketene di- and tri-merization to more complex precursors could readily open the route to highly functionalized symmetrical cyclobuta-1,3-diones and cyclohexa-l,3,5-triones. We report herein the results on three substrates containing either a C=C double bond or a protected glycol moiety as illustrative functionahzed groups. The nature of the substituents is found to be crucial: while cyclopentenyl and more constrained dioxolanocyclo-pentenyl precursors efficiently dimerize, a diallylic derivative fails. At the millimolar scale, methoxide-catalyzed trimeriza-tion shows limited reproducibility, even for the reported substrate tetramethylcyclobuta-l,3-dione. However, systematic studies, including the use of microwaves, demonstrate that formation of symmetrical trimers is favored under solvent-free conditions and conventional heating, which allowed us to isolate and characterize trispiro[4.1.4.1.4.1]octadeca-2,9,15-tri-ene-6,12,18-trione.