Modular synthesis of tetrahydrofluorenones from 5-alkylidene Meldrum's acids.

The one-pot synthesis of tetrahydrofluorenones, the core 6-5-6 tricyclic structural motif found in norditerpenoid natural products, from alkylidene Meldrum's acids via thermal Diels-Alder/BF3.OEt2-catalyzed Friedel-Crafts acylation reactions is described. A series of tetrahydrofluorenones was assembled in good yields, and the Diels-Alder/Friedel-Crafts acylation protocol allowed modification of the substitution within the rings.