Synthesis of the Mammea coumarins. Part 3. The insecticidal coumarins of the mammea E series, mammea D/BB, and a dihydrocoumarin of the mammea C series

Abstract

A dihydrocoumarin metabolite of Mammea africana has been prepared by Lewis acid-mediated acylation of 5,7-dihydroxy-4-pentyl-3,4-dihydrocoumarin (available by hydrogenation of the corresponding coumarin). Acylation of 4-(1-methylpropyl)- and 4-(1-acetoxypropyl)-5,7-dihydroxycoumarin, each prepared by Pechmann condensation of phloroglucinol with the appropriate β-keto ester, gave 8-acylcoumarins that have been C-alkylated with 3-methylbut-2-enyl bromide to provide, respectively, mammea D/BB (ferruol A), and the natural insecticidal 4-(1-acetoxypropyl)coumarins of M.americana, mammea E/BA and E/BB; C-alkylation with 3,7-dimethylocta-2,6-dienyl chloride of 4-(1-acetoxypropyl)-5,7-dihydroxy-8-(2-methylbutyryl) coumarin afforded surangin B, an insecticidal component of M.longifolia.