title: Gold(I)-Catalyzed Generation of the Two Components of a Formal [4+2] Cycloaddition Reaction for the Synthesis of Tetracyclic Pyrano[2,3,4-de]chromenes.
abstract: Ortho-Alkynylbenzaldehydes have been widely used to generate isochromenylium derivatives through gold-catalyzed cycloisomerization. These isochromenylium derivatives have been exploited as formal diene derivatives for reactions with different dienophiles. Herein, we describe the behavior of ortho-alkynylsalicylaldehydes, a particular case of ortho-alkynylbenzaldehydes. The gold-catalyzed cycloisomerization of ortho-alkynylsalicylaldehydes delivers an unusual heterodiene derivative that reacts with electron-rich alkenes through a formal [4+2] cycloaddition. In this reaction, both the diene and dienophile are generated in situ through gold-catalyzed cycloisomerization of appropriate alkynamines or alkynols. This reaction was used to synthesize complex tetracyclic pyrano[2,3,4-de]chromenes from two very simple starting materials (an ortho-alkynylsalicylaldehyde and an alkynamine or alkynol) with complete atom economy and with selective formation of bonds, cycles, and stereocenters.
authors.affiliation: Instituto Universitario de Química Organometálica "Enrique Moles", Universidad de Oviedo, Julián Clavería, 8, E-33006, Oviedo, Spain.
authors.forename: Tamara
authors.initials: T
authors.lastname: Arto
authors.affiliation: Instituto Universitario de Química Organometálica "Enrique Moles", Universidad de Oviedo, Julián Clavería, 8, E-33006, Oviedo, Spain. fjfv@uniovi.es.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Fañanás
authors.affiliation: Instituto Universitario de Química Organometálica "Enrique Moles", Universidad de Oviedo, Julián Clavería, 8, E-33006, Oviedo, Spain. frodriguez@uniovi.es.
authors.forename: Félix
authors.initials: F
authors.lastname: Rodríguez
keywords: cascade reactions; cycloaddition; gold; homogeneous catalysis; synthetic methods