Regiochemically flexible substitutions of di-, tri-, and tetrahalopyridines: the trialkylsilyl trick
摘要：
[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 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 most remote from the bulky 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 the nucleophile is invariably found to occupy the nitrogen-neighboring position.
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关键词：
Substitution reaction (regioselective arom. regiochem. flexible substitutions of di tri and tetrahalopyridines substitution regioselective polyhalopyridine
DOI：
10.1021/jo047962z
被引量：
年份：
2005
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