FULL PAPER The Microwave-assisted Organocatalyzed Rearrangement of Pro- pargyl Vinyl Ethers to Salicylaldehyde Derivatives: A Combined Experimental and Theoretical Study

Herein we describe the microwave-assisted imidazolecatalyzed transformation of propargyl vinyl ethers (PVEs) into multisubstituted salicylaldehyde motives. The reaction is instrumentally simple, scalable and tolerates a diverse grade of substitution at the propargylic position of the staring PVE. The generated salicylaldehyde motives incorporate a broad range of topologies, spanning from simple aromatic monocycles to complex fused polycyclic systems. The reaction is highly regioselective and operates under symmetry-breaking conditions. The preparative power of this reaction has been demonstrated in the first total synthesis of morintrifolin B (19), a benzophenone metabolite isolated from the small tree Morinda citrifolia L. A computational DFT study of the reaction has been accomplished, with full agreement between calculated values and observed experimental results. The theoretically calculated values support a domino mechanism comprising a propargyl Claisen rearrangement, a [1,3]-H shift, a [1,7]-H shift (enolization), a 6-electrocyclization and an aromatization reaction.