Acetamidines and acetamidoximes containing an electron-withdrawing group at the α-carbon atom: their use in the synthesis of nitrogen heterocycles (review)*

Abstract

Acetamidines and acetamidoximes containing an electron-withdrawing substituent at the α-position often exhibit unusual characteristics for compounds of these types. This is due to the presence of an "active" methylene group in the molecules of the compounds. This review is devoted to the most important syntheses of heterocyclic compounds from amidines and amidoximes involving the "active" methylene group. Amidines are important starting compounds in the synthesis of nitrogen heterocycles. In most of the reactions they act as N,N-dinucleophiles and deliver the triad of N–C–N atoms into the ring of the obtained heterocycle. They are widely used in the synthesis of pyrimidines and imidazoles. Acetamidines of type 1, containing an electron-withdrawing substituent at the α-position, have a different type of reactivity. The α-carbon atom in these compounds is a nucleophile that is often stronger than the nitrogen atoms. This is due to the fact that in the free base form these amidines exist as the