One-Pot Organocatalytic Tandem Aldol/Polycyclization Reactions between 1,3-Dicarbonyl Compounds and [alpha],[beta],[gamma],[delta]-Unsaturated Aldehydes for the Straightforward Assembly of Cyclopenta[b]furan-Type Derivatives: New Insight into the Knoevenagel Reaction

A new cascade pathway viable for Knoevenagel chemistry that involves the coupling between 1,3-dicarbonyl systems and [alpha],[beta],[gamma],[delta]-unsaturated aldehydes has been developed. The process comprises the combination of a classic aldol-type condensation and a rare spontaneous metal-free cycloisomerization, representing a convergent and innovative approach for the stereoselective synthesis of cyclopenta[b]furan-type derivatives. The scope and limitations with respect to both reaction partners and mechanistic features were investigated. Meaningfully, our study provides valuable guidance concerning the structural and electronic effects controlling the reactivity of conjugated polyene carbonyl systems.