Sequential Functionalization of Pyrazole 1-Oxides via Regioselective Metalation: Synthesis of 3,4,5-Trisubstituted 1-Hydroxypyrazoles
A range of 3,5-diarylated and 3,4,5-triarylated 2-(4-methoxybenzyl)pyrazole 1-oxides have been prepared by regioselective deprotonation at C-5 or bromine−magnesium exchange at C-3 or C-4 followed by transmetalation with ZnCl2 and palladium(0)-catalyzed cross-coupling. Furthermore, the metalated pyra...
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Published in: | Journal of organic chemistry 2002-05, Vol.67 (11), p.3904-3907 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | A range of 3,5-diarylated and 3,4,5-triarylated 2-(4-methoxybenzyl)pyrazole 1-oxides have been prepared by regioselective deprotonation at C-5 or bromine−magnesium exchange at C-3 or C-4 followed by transmetalation with ZnCl2 and palladium(0)-catalyzed cross-coupling. Furthermore, the metalated pyrazole 1-oxides could be trapped with electrophiles. The sequential metalation/functionalization of the pyrazole 1-oxides may follow the order C-5, C-3, C-4, or alternatively the order C-3, C-5, C-4. The 4-methoxybenzyl group of the functionalized 2-(4-methoxybenzyl)pyrazole 1-oxides could be removed by treatment with TFA and i-Pr3SiH in CH2Cl2, providing the corresponding functionalized 1-hydroxypyrazoles. |
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ISSN: | 0022-3263 1520-6904 |
DOI: | 10.1021/jo015997i |