Metalated 1-(p-Methoxybenzyl)pyrazole: A Structural Chameleon

When treated with either butyllithium or lithium diisopropylamide, 1‐(p‐methoxybenzyl)pyrazole undergoes metalation at the exocyclic α‐position but mutates to the 5‐lithio species in the course of few minutes or hours. Trapping the intermediates with a rapidly reacting electrophile such as chlorotri...

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Bibliographic Details
Published inEuropean Journal of Organic Chemistry Vol. 2006; no. 10; pp. 2417 - 2422
Main Authors Ondi, Levente, Schlosser, Manfred
Format Book Review Journal Article
LanguageEnglish
Published Weinheim WILEY-VCH Verlag 01.05.2006
WILEY‐VCH Verlag
Wiley
Subjects
Butyllithium
Chemistry
Chemistry, Organic
Isomerization
Lithium diisopropylamide
Metalation
Physical Sciences
Pyrazoles
Regioselectivity
Science & Technology
regioselectivity
FUNCTIONALIZATION
isomerization
ALPHA-LITHIATION
lithium diisopropylamide
butyllithium
pyrazoles
metalation
ACIDITY
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Summary:When treated with either butyllithium or lithium diisopropylamide, 1‐(p‐methoxybenzyl)pyrazole undergoes metalation at the exocyclic α‐position but mutates to the 5‐lithio species in the course of few minutes or hours. Trapping the intermediates with a rapidly reacting electrophile such as chlorotrimethysilane or carbon dioxide offers selective access to either of the two possible regioisomers. On the other hand, the relatively inert 1‐iodobutane and butyl trifluoromethanesulfonate (“triflate”) inevitably give rise to product mixtures, as the 5‐lithio species is more slowly intercepted than it can revert to the α‐metallomer by a rapid, though intermolecular, dynamic equilibration process. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Bibliography:ArticleID:EJOC200600029
ark:/67375/WNG-16SGSH81-5
istex:A62ADB8AFAA2E627E649291217BB810536E3F945
ISSN:1434-193X
1099-0690
DOI:10.1002/ejoc.200600029