title: Regiochemically flexible substitutions of di-, tri-, and tetrahalopyridines: the trialkylsilyl trick.
abstract: [reactions: see text] 2,4-Difluoropyridine, 2,4-dichloropyridine, 2,4,6-trifluoropyridine, 2,4,6-trichloropyridine and 2,3,4,6-tetrafluoropyridine react with standard nucleophiles exclusively at the 4-position under halogen displacement. However, the regioselectivity can be completely reversed if a trialkylsilyl group is introduced in the 5-position of the 2,4-dihalopyridines or in the 3-position of the 2,4,6-trihalopyridines or 2,3,4,6-tetrahalopyridine. Then only the halogen most remote from the bulky silyl unit (at the 2-position in the case of the 2,4-halopyridines, at the 6-position with the other substrates) gets involved in the exchange process. After removal of the silyl protective group the nucleophile is invariably found to occupy the nitrogen-neighboring position.
authors.affiliation: Institute of Chemical Sciences and Engineering (ISIC-BCh), Ecole Polytechnique Fédérale, CH-1015 Lausanne, Switzerland. schlosser@epfl.ch
authors.forename: Manfred
authors.initials: M
authors.lastname: Schlosser
authors.forename: Carla
authors.initials: C
authors.lastname: Bobbio
authors.forename: Thierry
authors.initials: T
authors.lastname: Rausis