Synthesis of Azulenone Skeletons by Reaction of 2-Phenyl-2-acylketenes [RCO(Ph)C=C=O] with Alkynyl Ethers: Mechanistic Aspects and Further Transformations

A method is described for a mild and efficient synthesis of azulenone skeletons via the addition reactions of 2-phenyl-2-acylketenes with 1-alkynyl ethers. A mechanism is presented to account for both azulenone formation as well as the solvent and substrate dependency of a competitive pyrone formation. The azulenone rings have been subsequently transformed into both substituted azulenes or hydroazulenes by derivatization and/or decarboxylation of an angular carboxyl substituent or by hydrogenation.