| 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 2 H-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. |
