Applications of the formal oxa-[3+3] cycloaddition to natural product synthesis

Abstract

For several years in our laboratory we have investigated the formal [3 + 3] cycloaddition. This is a condensation reaction that occurs between an unsaturated aldehyde and a 1,3-diketone or equivalent. The reaction results in a new 2H-pyran or 2H-pyridine fused to the diketone. Chapter I of this thesis concentrates on new developments in the area of oxa-[3 + 3] cycloaddition reaction, in particular, Lewis acid catalyzed version of this reaction. Synthetic scope and limitations of this new methodology are discussed. Chapter II describes synthetic approaches towards naturally occurring chromenes and chromanes. Our total syntheses of such compounds, rhododaurichromanic acid A and B, methyl ester of daurichromenic acid and hongoquercin A, are discussed in detail. Unusual, exo-type polyene cyclization and unique cationic [2 + 2] cycloaddition are also discussed, through divergent syntheses of rhododaurichromanic acid A and hongoquercin A. Total syntheses of daldiniapyrone, annularin B and F are described in the last chapter.