Synthesis of New Cardanol Derivatives through Combined Iodination/Palladium-Catalysed Cross-Coupling Reactions

Abstract

A versatile approach to the synthesis of new cardanol derivatives through a combination of aromatic iodination of 3-n-pentadecylphenol and palladium-catalysed cross-coupling reactions has been developed. The extent of aromatic iodination is controlled by stoichiometry and affords either the mono-, di- or tri-iodo-cardanol derivatives. Suzuki, Heck and Sonogashira protocols were successfully applied for the vinylation, arylation and alkynylation of the iodo-cardanols. 2,4-Diiodo-5-n-pentadecylphenol underwent an unusual sequential regioselective dehalogenation/vinylation reaction. Sequential alkynylation/cyclisation of 2-iodo-3-n-pentadecylphenol derivatives were also investigated.

Key words

aromatic substitution - halogenation - palladium - Heck reaction - cross-coupling

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18

The antioxidant properties of 3a,c were determined by kinetic measurements (inhibition rate constants K_inh M^-1s^-1); The inhibition rate constants for 3a,c are 6.2 × 10^-3 M^-1s^-1 and 6.5 × 10^-3 M^-1s^-1, respectively. For comparison, the inhibition rate constant of the commercial antioxidant 2,6-di-tert-butyl-4-methylphenol (BHT) is 2.6 × 10^-4 M^-1s^-1.