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
N-未取代的吡唑1易于以一锅法以中等到良好的总收率转化为5取代的[与3取代的8的互变异构体]衍生物2,同时使用甲醛进行N保护和介导5位的锂化反应。位置。所述dilithiohemiaminals 5与亲电子在吡唑的5位反应以得到5-取代的1- lithioxymethylpyrazoles 6中经历温和的条件下顺利dehydroxymethylation(酸水解或硅胶),得到N-未取代的5(3) -取代的吡唑。