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    Microwave-Assisted Organocatalyzed Rearrangement of Propargyl Vinyl Ethers to Salicylaldehyde Derivatives: An Experimental and Theoretical Study

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    The microwave-assisted imidazole-catalyzed transformation of propargyl vinyl ethers (PVEs) into multisubstituted salicylaldehydes is described. The reaction is instrumentally simple, scalable, and tolerates a diverse degree of substitution at the propargylic position of the starting PVE. The generated salicylaldehyde motifs incorporate a broad range of topologies, spanning from simple aromatic monocycles to complex fused polycyclic systems. The reaction is highly regioselective and takes place under symmetry-breaking conditions. The preparative power of this reaction was demonstrated in the first total synthesis of morintrifolin B, a benzophenone metabolite isolated from the small tree Morinda citrifolia L. A DFT study of the reaction was performed with full agreement between calculated values and 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 6π electrocyclization, and an aromatization reaction.This research was supported by the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (CTQ2011-28417-C02-02 and CTQ2013-45415-P), the UPV/EHU (UFI11/22 QOSYC), and the Basque Government (GV/EJ, grant IT-324-07). L.C. thanks Spanish MEC for a FPI grant and D.M.A. thanks CSIC for a JAE-intro grant. M.T.-S., M.O.-G., and F.P.C. thank the SGI/IZO- SGIker UPV/EHU and the DIPC for generous allocation of computational resources.Peer reviewe
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