title: Regioselective Pd-Catalyzed Synthesis of 2,3,6-Trisubstituted Pyridines from Isoxazolinones.
abstract: Substituted pyridines are prevalent heterocycles of fundamental importance. Their efficient regioselective preparation is often still a challenge despite a large number of reported synthetic methodologies. In this letter we report an operationally simple approach that makes use of readily accessible isoxazolinones. The protocol involves a Pd(II)-catalyzed C-regioselective 1,4-addition to vinylketones, followed by a Pd(0)-catalyzed transformation, which is assumed to proceed via vinylnitrene-Pd intermediates. Both hydrogen and air are necessary for the pyridine formation step and could be employed at ratios above the upper explosive limit thus avoiding a safety issue. This new strategy allows an effective, scalable and practical access to various previously unknown 2,3,6-trisubstituted pyridines.
authors.affiliation: Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rieckhoff
authors.affiliation: Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
authors.forename: Tina
authors.initials: T
authors.lastname: Hellmuth
authors.affiliation: Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
authors.forename: René
authors.initials: R
authors.lastname: Peters