1. Introduction
Epoxides (or oxiranes) are highly versatile intermediates in synthetic organic chemistry. Nature also uses them as intermediates in many key biosynthetic pathways. However, there are other functions of epoxides in biological systems. They can impart localised structural rigidity, confer cytotoxicity by alkylation, or be secondary metabolites [1]. The chemistry of epoxides is dominated by the reactions that involve opening of the strained three-membered heterocyclic ring by nucleophiles. Such reactions yield valuable bifunctional compounds. In nature, epoxide ring opening is catalysed by the phenolic proton of a tyrosine moiety [2]. But in laboratory, the cleavage usually occurs in non-aqueous media in presence of a Lewis acid catalyst like Al2O3, Li+, Mg2+ etc. Additionally often elevated temperature and excess of nucleophiles are required. There are a few reports where use of a catalyst has not been necessary [3,4]. For example, aminolysis of epoxide by an -amino acid ester proceeds smoothly in refluxing trifluoroethanol [3]. The same reactions fail in water. In contrast, aliphatic and aromatic amines are found to cleave an epoxide ring in water at room temperature without any Lewis acid catalyst [4]. Herein we report opening of an epoxide group present in a chelate ring of a metal complex by aromatic amines
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Results and discussion
Stirring of L with 4-methylaniline and 4-methoxyaniline in equimolar proportion in water at room temperature for 72 h without any Lewis acid catalyst gives L.H2O and L respectively (Scheme 1). The yield of L.H2O is 90% and that of L 70%. These are obtained in 60% yield when the reactants are refluxed in water for 14 h. But the yield goes on decreasing when increasingly more refluxing time is used. Earlier Moody et al have [5] studied opening of the epoxide ring in L in connection with their total synthesis of the pentacyclic marine alkaloid ascididemin from 1,10-phenanthroline (phen).