Hydrophilically functionalized pyrazoles from sugars

An effective and convenient protocol has been developed for the conversion of D-glucose and 6-O-alpha-D-glucopyranosyl-D-fructose (palatinose(R), isomaltulose) into 5-[(1'S)-1',2'-dihydroxyethyl]-1-phenylpyrazole-3-carboxaldehyde (4) and 5-[(1S)-2-(alpha-D-glucopyranosyloxy)-1-hydroxethyl])-1-phenylpyrazole-3-carboxaldehyde (5), key steps being the acetic anhydride-promoted dehydrative cyclization of the respective phenylosazones, and subsequent liberation of the N-acetylphenylhydrazone-blocked aldehyde function. Exploitation of the ensuing chemistry of 4 and 5 led to a variety of pyrazole building blocks with a diverse level of hydrophilic substituents (hydroxymethyl, dihydroxyethyl or glucosyl residues) and useful functional groups, such as chloro, cyano, aminomethyl, vinyl and acryloyl moieties. (C) 1998 Elsevier Science Ltd. All rights reserved.