Abstract
We have investigated the oxidative behaviour of natural compounds such as methyl abietate (1), farnesyl acetate (2), α-ionone (3), β-ionone (4), methyl linolelaidate (5), methyl linolenate (6) and bergamottin (7) with the oxidant system methyltrioxo-rhenium/H2O2/pyridine. The reactions, performed in CH2Cl2/H2O at 25 °C, have shown good regio- and stereoselectivity. The oxidation products were isolated by HPLC or silica gel chromatography and characterized by MS(EI), 1H-, 13C-NMR, APT, gCOSY, HSQC, TOCSY and NOESY measurements. The selectivity seems to be controlled by the nucleophilicity of double bonds and by stereoelectronic and steric effects.
Highlights
Oxyfunctionalization of cheap natural compounds is a useful protocol to obtain molecules widely employed in the fine chemicals-based industries as fragrances, flavors, and therapeutically active substances [1]
We have investigated the behaviour of methyl abietate (1), farnesyl acetate (2), α-ionone (3), β-ionone (4), methyl linolelaidate (5), methyl linolenate (6) and bergamottin (7) (Figure 1) which underwent oxidation reactions with MTO/H2O2/pyridine in CH2Cl2 at 25 °C (Table 1)
Since the configuration of the C-17 of 24, isolated from both grapefruit juice and its peel oil [47], is R, we have developed a synthetic strategy to obtain 24 by the highly regioselective oxidation of the C17-C18 double bond of bergamottin (7) with MTO/H2O2/pyridine to yield the racemic epoxide 23 and subsequent hydrolytic kinetic resolution (HKR) catalyzed by chiral (S,S)(salen)Co(III) complex [48,49,50]
Summary
Oxyfunctionalization of cheap natural compounds is a useful protocol to obtain molecules widely employed in the fine chemicals-based industries as fragrances, flavors, and therapeutically active substances [1]. The most commonly employed stoichiometric oxidants are organic peroxyacids, m-chloroperbenzoic acid (MCPBA). These oxidants are economically unattractive and are not selective for the preparation of acid-sensitive epoxides [2]. The epoxide ring opening can be minimized by employing pyridine as a basic ligand. In this report we have investigated the oxidation reactions of some natural compounds by MTO/H2O2/pyridine, leading to products of practical interest or of interest as synthons in the synthesis of fine chemicals, with the aim of assessing the parameters controlling the process
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