Synthesis Of 4H-Chromenes And Inulavosin Natural Products

4H-Chromenes have been a subject of consistent interest due to the presence of their structural motifs in a large number of natural products and their wide spectrum of pharmacological activities, such as antifungal, antiviral, and ant icancer properties. Different 4H-chromenes are required in an increasing number of applications, which makes the development of new 4H-chromene platforms a high priority. This thesis consists of three parts: Synthesis of 4H-chromenes, synthesis of inulavosin natural products, and the oxidation of aromatic alcohols to the corresponding aromatic aldehydes.An efficient synthesis of functionalized 4H-chromenes by the tandem reaction of β,γ-unsaturated α-ketoesters with 2-naphthols, 1-naphthols, and 1,3-dihydroxynaphtha- lenes has been accomplished with high selectivity and excellent yields in the presence of a catalytic amount of bismuth triflate [Bi(OTf)3, 5 mol%] under mild conditions.The aromatic aldehydes are required for the synthesis of β,γ-unsaturated α-ketoesters, which were preparied here by the oxidation of the corresponding benzyl alcohols. The reaction condtions were optimized, and the scope of the reaction was subsequ ently investigated.Inulavosin natural products, a melanogenesis inhibitor and piscicide isolated from Inula in 1995, are a category of hydride of chromenes. In view of its scaity in plants as well as the high cost for its extraction, it maybe a good solution to gain these compounds through organic synthesis. An efficient synthetic route was designed to accomplish the synthesis of inulavosin natural products. Inulavosin was synthesized with 1-hyd- roxy-3-methylbenzene as the starting material. The protected 1-hydroxy-3-methyl- benzene was converted to the intermediate by a Friedel-Crafts acylation with acetyl chloride. The self-condensation of the methylated intermediates generated the precursorsurn of inulvosin, which was converted to inulavoin via a debromination. By this method the other two inulavosin natural products were synthesized.