DEALKYLATION OF 4-PHOSPHORYLATED 5-ALKOXYPYRAZOLES - EASY SYNTHETIC ACCESS TO P-CHLORO YLIDES

The chlorination of 5-alkoxypyrazoles containing bis-(dialkylamino)- o r diphenylphosphino groups at the 4-position afforded highly unstable chlorophosphonium chlorides that dealkylated giving chlorobis(dialkyla mino)- and nium(3-methyl-5-oxo-1-phenyl-5H-pyrazol-4-yl)ides. The P-ch loro ylides do not react with aromatic aldehydes, but chlorine atoms a re easily substituted with OH, NH2 ArNH, and Et2N residues. They also exhibit basic properties and add hydrogen chloride with protonation at N-2. (C) 1998 John Wiley & Sons, Inc.