Synthesis of the acylphloroglucinols rhodomyrtone and rhodomyrtosone B

In a sequential three-component coupling syncarpic acid, 3-methylbutanal and an acylated phloroglucinol were combined to the hydroxy ketone 3. Acid catalysis converted 3 directly to the natural product rhodomyrtosone B (2). The other isomer, the antibiotic rhodomyrtone (1) was obtained from 3 in a sequence of acid-catalyzed cyclization, retro Friedel-Crafts reaction, and reacylation. In preliminary assays both compounds showed potent antibiotic activity.