title: Enantioselective multicomponent synthesis of fused 6-5 bicyclic 2-butenolides by a cascade heterobicyclisation process.
abstract: The successive coupling of an alkoxy(aryl/heteroaryl)carbene complex of chromium with either a ketone or an imide lithium enolate and then a 3-substituted (H, TMS, PhCH(2), PhCH(2)CH(2), Me) propargylic organomagnesium reagent has afforded novel hydroxy-substituted bicyclic [4.3.0]-γ-alkylidene-2-butenolides with three modular points that has allowed the efficient introduction of molecular complexity, including a homopropargylic alcohol core. The selective formation of these five- or six-component heterobicyclisation products is the result of the regioselective integration of the Grignard reagent as a propargyl fragment followed by a cascade CO/alkyne/CO insertion, ketene trapping and elimination sequence. By using lithium enolates of chiral N-acetyl-2-oxazolidinones and the corresponding propargylic organocerium reagents, both enantiomers of these bicyclic heterocycles were efficiently prepared with very high enantiomeric purity. Architecturally, these fused bicyclic butenolides are characterised by a highly unsaturated and oxygenated core and they exhibit strong blue fluorescence in solution.
authors.affiliation: Instituto Universitario de Química Organometálica Enrique Moles, Unidad Asociada al CSIC, Universidad de Oviedo, Julián Clavería 8, 33006 Oviedo, Asturias, Spain.
authors.forename: Marcos G
authors.initials: MG
authors.lastname: Suero
authors.forename: Raquel
authors.initials: R
authors.lastname: De la Campa
authors.forename: Laura
authors.initials: L
authors.lastname: Torre-Fernández
authors.forename: Santiago
authors.initials: S
authors.lastname: García-Granda
authors.forename: Josefa
authors.initials: J
authors.lastname: Flórez