Studies On Gold And Platinum Catalyzed Cyclization Of Conjugated Enyne Carbonyl Compouds With Alkenes To Construct Cyclopentafuran Structures

Gold and platinum are the6th period later transition elements, they not only act as transition metals, but also as lewis acids, which are also called π-acid. The individual lewis acids show high activity to the alkyne group. In recent years, the reactions via gold, platinum-catalyzed have drawn much attention of chemists.The synthesis of highly substituted furans has attracted tremendous interest for several decades, resulting from both the importance of the five-memembered heterocycles in natural products and pharmaceuticals and the uniqueness as a useful intermediates in total syntheses. Therefore, the atom-economical and region-defined approaches to synthesis of highly substituted furans have particularly held our attention.Our groups have many studies on gold and platinum catalysis, this thesis is concemed with studies on the reaction of conjugated enyne carbonyl compouds and alkenes catalyzed by gold and platinum. It is divided into two parts as follows:1. We choose2-(1-alkynyl)-3-aryl-2-propenals as subtrates, the oxygen of the carbonyl group, used as a nucleophile, attacks alkynes which activated by platinum to form an oxonium ion intermediate, which subsequently isomerizes to a furan carbocation. Then, the nucleophilic attack of electron-rich olefins to the carbocation and [3+2] cyclization occurs subsequently to obtain polysubstituted4H-cyclopenta[b]furans. The reaction shows a good to excellent yield. and high chemo-and regioselectivity.2. The substrate2-benzylidene-1,4-diphenylbut-3-yn-l-one and ethene-1,1-diyldibenzene can not react to the4H-cyclopenta[b]furans catalyzed by platinum. To our surprise, they can be cyclizated to obtain a4H-cyclopenta[c]furans in the presence of gold. The reaction shows good yield and regioselectivity.