Long chain phenols. Part 17. The synthesis of 5-[(Z)-pentadec-8-enyl]resorcinol, ‘cardol monoene,’ and of 5-[(ZZ)-pentadec-8,11-dienyl]-resorcinol dimethyl ether, ‘cardol diene’ dimethyl ether

Abstract

Two unsaturated compounds in the ‘cardol’ series, an important component phenol from Anacardium occidentale, have been synthesised. 3,5-Dimethoxybenzaldehyde interacted with OH-protected 6-chlorohexan-1-ol in the presence of lithium to give, after acidic treatment, 1-(3,5-dimethoxyphenyl)heptane-1,7-diol which was hydrogenolysed selectively to 7-(3,5-dimethoxyphenyl)heptan-1-ol. Conversion into the bromide and alkylation of lithio-oct-1-yne gave 5-(pentadec-8-ynyl)resorcinol dimethyl ether which was selectively converted into the 8-(Z)-alkene. Demethylation with lithium iodide gave 5-[(Z)-pentadec-8-enyl]resorcinol which was identical to ‘cardol monoene’. Reaction of 7-(3,5-dimethoxyphenyl)heptyl bromide with the lithium derivative of OH-protected propargyl alcohol, gave after acidic treatment 10-(3,5-dimethoxyphenyl)dec-2-yn-1-ol, the bromide of which with pent-1-ynylmagnesium bromide afforded 5-pentadec-8,11-diynylresorcinol dimethyl ether. Selective hydrogenation yielded 5-[(ZZ)-pentadeca-8,11-dienyl]resorcinol dimethyl ether identical with the dimethyl ether of ‘cardol diene.’