Epoxides Lab Report

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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
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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).
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When the refluxing time is 1 h in the case of 4-methylaniline, the yield is 30%, and when it is 4 h in the case of 4-methoxyaniline, the yield is 45%. The yield goes on decreasing in each case when refluxing time is increasingly more than that specified. Their proton NMR spectra show that in each case only one sharp methyl signal is obtained. The 1H NMR spectrum of [ZnL3](ClO4)2.4H2O is shown in Fig. 2. This implies that only one diastereomer out of the 23 possibilities is formed. Thus the aminolysis of the epoxide rings in [ZnL3]2+ by 4-substituted anilines is diastereoselective. The same diastereomers are obtained when L.H2O and L are reacted directly with Zn(ClO4)2.6H2O in tetrahydrofuran (THF) at room temperature in 70-80 % yield. L.H2O yields [ZnL3](ClO4)2.0.75THF.5H2O but L gives [ZnL3](ClO4)2.4H2O the same complex obtained by aminolysis of [ZnL3](ClO4)2.2H2O by 4-methoxyaniline in water. Such selectivity is not common in inorganic synthesis [9.10]. We have found that two diastereomers are obtained when L.H2O is reacted with Ru(phen)2Cl2.2H2O in equimolar proportion in 1:1 (v/v) methanol-water mixture under refluxing condition to synthesise [Ru(phen)2L](ClO4)2.2H2O. This conclusion is based on the observation of two methyl signals in the

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