title: Synergistic Rhodium/Phosphoric Acid Catalysis for the Enantioselective Addition of Oxonium Ylides to ortho-Quinone Methides.
abstract: We report herein a powerful and highly stereoselective protocol for the domino-type reaction of diazoesters with ortho-quinone methides generated in situ to furnish densely functionalized chromans with three contiguous stereogenic centers. A transition-metal and a Brønsted acid catalyst were shown to act synergistically to produce a transient oxonium ylide and ortho-quinone methide, respectively, in two distinct cycles. These intermediates underwent subsequent coupling in a conjugate-addition-hemiacetalization event in generally good yield with excellent diastereo- and enantioselectivity.
authors.affiliation: Institut für Organische Chemie, Universität Leipzig, Johannisallee 29, 04103, Leipzig, Germany.
authors.forename: Santosh Kumar
authors.initials: SK
authors.lastname: Alamsetti
authors.affiliation: Institut für Organische Chemie, Universität Leipzig, Johannisallee 29, 04103, Leipzig, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Spanka
authors.affiliation: Institut für Organische Chemie, Universität Leipzig, Johannisallee 29, 04103, Leipzig, Germany. schneider@chemie.uni-leipzig.de.
authors.forename: Christoph
authors.initials: C
authors.lastname: Schneider
keywords: ortho-quinone methides; oxonium ylides; phosphoric acids; rhodium; synergistic catalysis