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Acidity and alkylation of 4‐phenyl‐3,5‐dihydroxypyrazole and its derivatives. C versus O and N alkylation
Author(s) -
Zvilichovsky Gury,
David Mordechai
Publication year - 1988
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570250507
Subject(s) - chemistry , alkylation , diazomethane , ring (chemistry) , medicinal chemistry , methyl iodide , reagent , alkyl , nitrogen , dimethyl sulfate , iodide , organic chemistry , carbon fibers , catalysis , materials science , composite number , composite material
4‐Phenyl‐3,5‐dihydroxypyrazole is a relatively strong acid, with a p K a of 3.70. The effect of substitution, both in the phenyl ring and on the heterocyclic ring, on the acidity was studied. Electron attracting groups on the phenyl group enhance the acidity. Selective replacement by an alkyl group of one or two of the heterocyclic hydrogens lowers the acidity. Meerwein reagent, as well as methyl iodide bring about alkylation on carbon, whereas diazomethane and diethyl sulfate do not. Michael addition proceeds through both carbon and nitrogen.