Regiochemically Flexible Substitutions of Di-, Tri-, and Tetrahalopyridines: The Trialkylsilyl Trick
作者:Manfred Schlosser、Carla Bobbio、Thierry Rausis
DOI:10.1021/jo047962z
日期:2005.4.1
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.
Rerouting Nucleophilic Substitution from the 4-Position to the 2- or 6-Position of 2,4-Dihalopyridines and 2,4,6-Trihalopyridines: The Solution to a Long-Standing Problem
作者:Manfred Schlosser、Thierry Rausis、Carla Bobbio
DOI:10.1021/ol047826g
日期:2005.1.1
2,4-Difluoro-, 2,4,6-trifluoro-, and 2,3,4,6-tetrafluoropyridine undergo nucleophilic substitution preferentially if not exclusively at the 4-position. However, after the introduction of a trialkylsilyl group at C-3 or C-5, the halogen at the 6-(2-)position is displaced selectively. This synthetically valuable regiocontrol can also be realized with other halopyridines such as 2,4-dichloro- and 2,4,6-trichloropyridine.
Removal of Fluorine from and Introduction of Fluorine into Polyhalopyridines: An Exercise in Nucleophilic Hetarenic Substitution
作者:Carla Bobbio、Thierry Rausis、Manfred Schlosser
DOI:10.1002/chem.200400837
日期:2005.3.4
Starting fromsix industrially available fluorinated pyridines, an expedient access to all three tetrafluoropyridines (2-4), allsix trifluoropyridines (5-10), and the five non-commercial difluoropyridines (11-14 and 16) was developed. The methods employed for the selective removal of fluorinefrom polyfluoropyridines were the reduction by metals or complex hydrides and the site-selective replacement
Straightforward Synthesis of Halopyridine Aldehydes via Diaminomethylation
作者:Georgyi Koidan、Serhii Zahorulko、Anastasiia Hurieva、Tetiana Shvydenko、Eduard B. Rusanov、Alexander B. Rozhenko、Uwe Manthe、Aleksandr Kostyuk
DOI:10.1002/chem.202301675
日期:2023.10.2
Pyridines featuring two or more halogen atoms react with silylformamidine via insertion into the most acidic C−H bond either at the γ or β-positions affording the corresponding aminals. Their hydrolysis gave aldehydes. The reaction proceeds via H-abstraction from pyridines by the strong base-carbenic form of silylformamidine followed by formation of C−C bond between the formamidinium cation and the