Acid promoted synthesis of cyclic 1,3-dione fused symmetrical 2,8-dioxabicyclo[3.3.1]nonanes

Abstract

A one-pot access to cyclic 1,3-dione fused symmetrical 2,8-dioxabicyclo[3.3.1]nonanes (4) via acetic acid-mediated reaction of β-enamino ketones (1) and 1,3-cyclohexanediones (2) by heating under reflux is reported. The reaction proceeds via intramolecular cyclization of intermediate 2,2′-(3-oxo-3-arylpropane-1,1-diyl)bis(3-hydroxy-5,5-dimethylcyclohex-2-en-1-one) (3) and is highly selective towards the formation of product 4. Unlike similar reactions, the presence of trifluoroacetic acid in a toluene medium affords xanthenes (5) exclusively.