821016-36-8Relevant articles and documents
The 4-methoxybenzyl (PMB) function as a versatile protecting group in the synthesis of N-unsubstituted pyrazolones
Eller, Gernot A.,Holzer, Wolfgang
, p. 2537 - 2555 (2007/10/03)
Starting from diethyl ethoxymethylenemalonate and 4-methoxy-benzylhydrazine (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.