Online article for Non-subscribers

Pay per view

Heterocycles has a pay-per-view service for Non-subscribers.
You will be able to directly purchase the full text article through PayPal.
Your purchased Paper can be downloaded after the payment is completed.
An e-mail will be sent the URL to download the paper.
If you have any questions, please contact:

Price: ¥ 4,400 (Yen only)
Period: This Article can be accessed for 7 days.

Paper | Regular issue | Vol 63, No. 11, 2004, pp.2537-2555
Published online, 17th September, 2004
DOI: 10.3987/COM-04-10190
The 4-Methoxybenzyl (PMB) Function as a Versatile Protecting Group in the Synthesis of N-Unsubstituted Pyrazolones

Gernot A. Eller and Wolfgang Holzer*

*Institute of Pharmaceutical Chemistry, University of Vienna, Pharmaziezentrum, Althanstraße 14, A-1090 Vienna, Austria


Starting from diethyl ethoxymethylenemalonate and 4-methoxybenzylhydrazine (PMB-NHNH2) 2-(4-methoxybenzyl)-2,4-dihydro-3H-pyrazol-3-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 (1H, 13C, 15N) with the obtained compounds are presented.