Total synthesis and repudiation of the helianane family.

Total syntheses of two structures purported as (+)-heliananes were completed in six pots. Spectral comparisons, between the synthetic and natural compounds, revealed a misassignment of the eight-membered ring in the heliananes. The key step in the syntheses of the proposed structures and the confirmation of their actual structures was a diastereoselective inverse-demand Diels-Alder reaction between an optically active enol ether and an ortho-quinone methide species, which was generated in situ at low temperature by the sequential addition of methylmagnesium bromide and di-tert-butyl dicarbonate to a salicylaldehyde.