The 4-methoxybenzyl (PMB) function as a versatile protecting group in the synthesis of N-unsubstituted pyrazolones | Health & Environmental Research Online (HERO)

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Citation
Tags

HERO ID

6849391

Reference Type

Journal Article

Title

The 4-methoxybenzyl (PMB) function as a versatile protecting group in the synthesis of N-unsubstituted pyrazolones

Author(s)

Eller, GA; Eller, GA; Holzer, W; Holzer, W

Year

2004

Is Peer Reviewed?

Yes

Journal

Heterocycles
ISSN: 0385-5414

Volume

Issue

Page Numbers

2537-2555

Web of Science Id

WOS:000225389700007

Abstract

Starting from diethyl ethoxymethylenemalonate and 4-methoxybenzylhydrazine (PMB-NHNH2) 2-(4-methoxybenzyl)-2,4-dihydro-3H-pyrazol3-one was prepared. Reaction of the latter with carboxylic acid chlorides / calcium hydroxide in 1,4-dioxane afforded 4-acyl-5-hydroxy-1-PMB-1H-pyrazoles, whereas with dimethylformamide diethyl acetal or benzaldehyde the corresponding (E)-4-dimethylaminomethylene or (E)-4-benzylidene products, respectively, were obtained. The PMB protecting group could be conveniently removed from the pyrazole nucleus by treatment with trifluoroacetic acid to give the N-unsubstituted pyrazolones. Detailed NMR spectroscopic investigations (H-1, C-13, N-15) with the obtained compounds are presented.<