A new simple and convenient method for the synthesis of substituted 2,6,9-trioxabicyclo[3.3.1]-nona-3,7-dienes from arylmalondialdehydes

A new convenient synthesis of substituted 2,6,9-trioxabicyclo[3.3.1]-nona-3,7-dienes is described. These new ‘bridged bis-dioxines’ were obtained in moderate to good yields by dimerization of the corresponding arylmalondialdehydes in the presence of 0.5 equiv of TMSOTf. The structure of the nitro derivative 1e has been proven by X-ray crystallography. A mechanism for this reaction is proposed.