A synthesis of 2-aza-l,3-butadienes 3 substituted with a phosphonate group in the 3-position is described. The key step is the olefination reaction of bisphosphonylalkyl imino compounds 2, with aldehydes in the presence of base. Heterocyclisation of 2-azatrienes 5 afforded substituted 2-phosphorylated pyridines 6. o 1999 Elsevier Science Ltd. All rights reserved.
2-Aza-1,3-butadienes represent an important class of compounds, and have become useful key intermediates in organic synthesis for the construction of both heterocyclic systems and open chain polyfunctionalized compounds [1]. The synthesis and some reactions of electronically neutral 2-azadienes [2], as well as of heterodienes with electron-donating substituents [3], have been reported. However, electron-poor 2-azadienes have received much less attention, probably owing to the lack of general methods for their synthesis [1]. Azabutadienes of this type were limited to 3-or 4-substituted electron-deficient heterodienes derived from ~-[4] (Ib, Scheme l) or p-amino acids [5] (Ia, Scheme l) as well as to 4,4-[6a] and to 3,4-electron-withdrawing substituted 2-azadienes [5a,6b,c], and these kinds of electron-poor 2 azadienes derived from amino acids (I) have been used not only in the synthesis of heterocyclic systems through cycloaddition reactions [4][5][6][7] but also for the synthesis of functionalized amino acid derivatives [81].
la
Ib II
Scheme 1
Nevertheless, 1-aminoalkylphosphonic acids, the phosphonic analogues of important amino acids, and their phosphapeptide derivatives, are a unique class of simple mimetics of amino