: B 9451 (OTTO) 2,5-Bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone, 96% Cas 16691-79-5 - used as a building block in organic chemistry. It is also used in the synthesis of hetrocyclic rings and in the Weiss-Cook reaction, which involves the preparation of cis-bicyclo[3.3.0]octane-3,7-dione by reacting with diacyl (1,2 ketone). Its presence in human urine is used as a diagnostic test for the overgrowth of harmful gut flora such as Candida albicans.