A Synthetic Approach to PW2-Like Compounds

The 9H-xanthene derivatives, like PW2, displayed a wide spectrum of bioactivities. Herein, we reported a rapid and simple synthetic route for compounds containing the xanthenic moiety in their structure and amides. The efficient preparation of novel 1,8-dioxo-2,3,4,5,6,7,8,9-octahydro-1-xanthen-9-ylacetic acid alkyl esters by multicomponent tandem Michaelcyclization reactions starting from cyclohexanediones and alkynes is described. Iodine and cerium (IV) ammonium nitrate were used for the oxidative aromatization step proving a series of 1,8-mono and dialkoxy-alkyl-xanthenyl-9-yl acetic acid esters in good yields. The proposed mechanism for the oxidative aromatization involves several organic transformations. The final step was the incorporation of an amide to mimic the PW2 structure that was prepared by hydrolysis of the esters, followed by the amide formation using N,N-dimethyl-1,3-propandiamine, and benzylamine.