title: Enantio- and diastereoselective access to distant stereocenters embedded within tetrahydroxanthenes: utilizing ortho-quinone methides as reactive intermediates in asymmetric Brønsted acid catalysis.
abstract: A protocol for the highly enantioselective synthesis of 9-substituted tetrahydroxanthenones by means of asymmetric Brønsted acid catalysis has been developed. A chiral binol-based N-triflyphosphoramide was found to promote the in situ generation of ortho-quinone methides and their subsequent reaction with 1,3-cyclohexanedione to provide the desired products with excellent enantioselectivities. In addition, a highly enantio- and diastereoselective Brønsted acid catalyzed desymmetrization of 5-monosubstituted 1,3-dicarbonyl substrates with ortho-quinone methides gives rise to valuable tetrahydroxanthenes containing two distant stereocenters.
authors.affiliation: Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen (Germany).
authors.forename: Chien-Chi
authors.initials: CC
authors.lastname: Hsiao
authors.forename: Hsuan-Hung
authors.initials: HH
authors.lastname: Liao
authors.forename: Magnus
authors.initials: M
authors.lastname: Rueping
mesh_terms: D002384:Catalysis; D045563:Indolequinones / Q000737:chemistry*; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D045563:Indolequinones; C068040:quinone methide
keywords: cyclization; enantioselectivity; heterocycles; organocatalysis; synthetic methods