Heterocyclic carbanions. Synthesis of 2-substituted imidazole and benzimidazoles and of 3-substituted pyrazoles by lithiation of N-(dialkylamino)methyl heterocycles
Formaldehyde: A Reagent for Simultaneous Protection of Heterocyclic NH and Activation of Alternative Locations to Electrophilic Attack. Part II. A New Synthetic Method for the 5(3)-Substitution of N-Unsubstituted Pyrazoles
作者:Alan R. Katritzky、Ping Lue、Kunihiko Akutagawa
DOI:10.1016/s0040-4020(01)81320-x
日期:1989.1
N-Unsubstituted pyrazole 1 is readily converted into 5-substituted [tautomeric with 3-substituted 8] derivatives 2 in moderate to good overall yields in a one-pot sequence, using formaldehyde both for N-protection and to mediate lithiation at the 5-position. The dilithiohemiaminals 5 react with electrophiles at the pyrazole 5-position to give 5-substituted 1-lithioxymethylpyrazoles 6 which undergo