Studies On Lewis Base Promoted Annulations Involving 1,2-Dicarbonyl Compounds

The highly efficient synthesis of cyclic compounds is an important research task in organic synthesis.Recently,Lewis base promoted annulations have attracted great attention from chemists.The annulation reactions promoted by the commonly used Lewis bases such as tertiary phosphine and tertiary amine usually have the merits such as mild and metal-free conditions,the ready availability of the start material,and therefore attract much research effort from organic chemists.In this thesis,we have explored the the tertiary phosphine and the tertiary amine promoted annulations involving 1,2-dicarbonyl compounds,which leads to the development of new approaches for two important five-membered heterocylces.The thesis includes the following several sections:1.The different tertiary phosphine and tertiary amine promoted annulation reactions have been briefly reviewed.The rich reactivity patterns of1,2-dicarbonyl compounds,especially their Kukhtin-Ramirez adducts formed with tertiary phosphine,have also been summarized.Furthermore,the aims of this thesis are discussed.2.A three-coordinate phosphorus reagent promoted[4+1]annulation of N-acyldiazenes with 1,2-dicarbonyl compounds has been explored.Under the optimized conditions,the reaction exhibits a broad substrate scope.Different types of 1,2-dicarbonyl compounds such as isatin,ethyl aroylformates and?-diketone can proceed well with different substituted N-acyldiazenes to give the 2,2,5-trisubstituted 1,3,4-oxadiazoles in moderate to excellent yields.Mechanistically,the reaction is initiated with the in situ formation of the Kukhtin-Ramirez adduct from the 1,2-dicarbonyl compound and the three coordinate phosphorus reagent,and most likely proceeds in a cascade conjugate addition-intramolecular substitution sequence.The reaction represents the first realization of the[4+1]annulation mode involving N-acyldiazenes as C₄synthon,and also provides an efficient synthesis of 2,2,5-trisubstituted1,3,4-oxadiazoles derivatives.3.Several ortho-substituted ethyl aroylformates have been synthesized,and the DBU-mediated intramolecular annulation of these substrates has been explored,leading to synthesis of 2,3-disubstituted benzofuran derivatives.Different types of substrates derived from ortho-hydroxybenzolyformats with ethyl 4-bromocrotonate,2-bromoacetophenone,diethyl bromomalonate or ethyl bromoacetate are all well tolerated,giving the 2,3-disubstituted benzofuran derivatives in moderate to high yields.4.The detailed experimental procedures and the charactering data of all new starting material and products have been attached.5.Summary.