The Synthesis of 5,11,17‐Trihalotetracyclo [13.3.1.1 3,7 .1 9,13 ]henicosa‐1 (19),3,5,7 (20),9,11,13 (21), 15,17‐nonaene‐19,20,21‐triols and 5,11,17‐trihalo‐19,20,21‐trihydroxytetracyclo [13.3.1.1 3,7 . 1 9,13 ]henicosa‐1 (19),3,5,7 (20),9,11,13(21), 15,17‐nonaene‐8,14‐dione [1]. Cyclo‐derivatives of Phloroglucide Analogues

The synthesis of the title compounds ( 1 and 3 ) is described. Some of the compounds prepared were found to be active against a number of pathogenic microorganisms in vitro. Structure‐activity relationship is briefly discussed.