title: A practical route to enantiopure, highly functionalized seven-membered carbocycles and tetrahydrofurans: concise synthesis of (+)-nemorensic Acid.
abstract: Highly diastereoselective thermal [5C+2C] intramolecular pyrone-alkene cycloadditions can be achieved by introducing a homochiral p-tolylsulfinyl group at a suitable position of the alkene. The resulting adducts can be readily desulfinylated to give optically active 8-oxabicyclo[3.2.1]octane derivatives. Interestingly, switching from a sulfinyl to a sulfonimidoyl group allows one to reverse the direction of the diastereofacial selectivity and thereby produces oxa-bridged carbocyclic systems enantiomeric to those obtained from the sulfinyl precursors. Cleavage of the oxa-bridge on the desulfurated adducts yields highly functionalized seven-membered carbocyclic derivatives in enantiopure form. Alternative cleavage of the seven-membered carbocycle provides enantiomerically enriched tetrahydrofurans. We have exploited this reaction pathway for the synthesis of the naturally occurring enantiomer of nemorensic acid.
authors.affiliation: Departamento de Química Orgánica y Unidad Asociada al CSIC Universidad de Santiago de Compostela 15782 Santiago de Compostela, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: López
authors.forename: Luis
authors.initials: L
authors.lastname: Castedo
authors.forename: José L
authors.initials: JL
authors.lastname: Mascareñas