Synthesis of the Mammea coumarins. Part 2. Experiments in the mammea E series and synthesis of mammea E/AC

Abstract

From condensations between ethyl 4-acetoxy-3-oxohexanoate and acyl phloroglucinols, 5- or 7-acyl benzo[b]furans (5) were isolated rather than the desired 4-(1-acetoxypropyl)-5,7-dihydroxy-6(or 8)-acylcoumarins. Related condensations between ethyl 4-bromo-3-oxohexanoate, or ethyl 4-chloro-3-oxobutanoate, and acyl phloroglucinols afforded either the desired 4-(1-haloalkyl)-5,7-dihydroxy-6(or 8)-acylcoumarins, or 6- or 8-acylfuro[4,3,2,-d,e][1]benzopyran-4(2H)-ones (11) by subsequent dehydrohalogenation. Attempted conversion of the 4-(1-haloalkyl)coumarins into 4-(1-acetoxyalkyl)coumarins with sodium acetate–acetic acid gave acylbenzofurans (5), with silver acetate in acetonitrile gave acylfurobenzopyranones (11) and with tetramethylammonium acetate gave the isomeric acylfurobenzopyranones (13). Allyiic bromination of 6-butyryl-5,7-dimethoxy-4-propylcoumarin and conversion of the 4-(1-bromopropyl) product to a 4-(1-acetoxypropyl)coumarin, followed by a difficult demethylation and subsequent C-prenylation afforded mammea E/AC, a 6-acyl isomer of one of the natural 8-acyl insecticidal Mammea coumarins; application of this sequence to 8-butyryl-5,7-dimethoxy-4-propylcoumarin failed at the demethylation stage.