Partial protection and substitution of L-threo-glycerol-1-ylpyrazoledione

Partial protection of the glycerolyl side-chain in 3-( L - threo -glycerol-1-yl)-1-phenyl-4,5-pyrazoledione 4-(phenylhydrazone) ( 2 ) was achieved via its acetonation; p -toluenesulfonylation then gave 3-(2,3,- O -isopropylidene-1- O - p -tolylsulfonyl- L - threo -glycerol-1-yl)-1-phenyl-4,5-pyrazoledione 4-(phenylhydrazone). Benzoylation of the 2,3-isopropylidene acetal of 2 gave 3-(1- O -benzoyl-2,3- O -isopropylidene- L - threo -glycerol-1-yl)-1-phenyl-4,5-pyrazoledione 4-(phenylhydrazone) that, upon deacetalation, gave 3-(1- O -benzoyl- L - threo -glycerol-1-yl)-1-phenyl-4,5-pyrazoledione 4-(phenylhydrazone), benzoylated to 1-phenyl-3-(1,2,3-tri- O -benzoyl- L - threo -glycerol-1-yl)-4,5-pyrazoledione 4-(phenylhydrazone). Debenzoylation followed by periodate oxidation gave the same aldehyde, 3-formyl-1-phenyl-4,5-pyrazoledione 4-(phenylhydrazone), as was obtained on similar treatment of 2 . Bromination of 2 afforded 1-( p -bromophenyl)-3-( L - threo -glycerol-1-yl)-4,5-pyrazoledione 4-( p -bromophenyl)-hydrazone, and that gave a monoisopropylidene acetal. The structures of these compounds were confirmed by i.r. spectroscopy.