title: Construction of chiral bridged tricyclic benzopyrans: enantioselective catalytic Diels-Alder reaction and a one-pot reduction/acid-catalyzed stereoselective cyclization.
abstract: An asymmetric two-step approach to chiral bridged tricyclic benzopyrans, core structures featured in various natural products, is described. In the synthesis, an unprecedented enantioselective catalytic decarboxylative Diels-Alder reaction is developed using readily available coumarin-3-carboxylic acids and aldehydes as reactants under mild reaction conditions. Notably, the decarboxylation-assisted release of the catalyst enables the process to proceed efficiently with high enantio- and diastereoselectivity. Furthermore, a one-pot procedure for either a LiAlH4 - or NaBH4 -mediated reduction with subsequent acid-catalyzed intramolecular cyclization of the Diels-Alder adducts was identified for the efficient formation of the chiral bridged tricyclic benzopyrans.
authors.affiliation: Department of Chemistry & Chemical Biology, University of New Mexico, Albuquerque, NM 87131 (USA) http://chemistry.unm.edu/faculty_bio/wwang.html.
authors.forename: Aiguo
authors.initials: A
authors.lastname: Song
authors.forename: Xishuai
authors.initials: X
authors.lastname: Zhang
authors.forename: Xixi
authors.initials: X
authors.lastname: Song
authors.forename: Xiaobei
authors.initials: X
authors.lastname: Chen
authors.forename: Chenguang
authors.initials: C
authors.lastname: Yu
authors.forename: He
authors.initials: H
authors.lastname: Huang
authors.forename: Hao
authors.initials: H
authors.lastname: Li
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
keywords: cyclization; decarboxylation; heterocycles; organocatalysis; synthetic methods