Preparation Of Polystyrene-Supported Organoselenium Reagents And Their Applications In Organic Synthesis

In this dissertation, the preparation of polystyrene-supported organoselenium compounds and their applications in organic synthesis were investigated.Firstly, Polystyrene-supported benzyl selenide has been prepared from 1% cross-linked polystyrene resin. This novel reagent was treated with LDA to produce polystyrene-supported a-seleno carbanions, which reacted with alkyl halides and epoxides, followed by stereospecific selenoxide syn-elimination to give olefins and allylic alcohols respectively. And also polystyrene-supported benzyl selenide can be regenerated and reused.Secondly, Polystyrene-supported selenomethyl-phosphonate and polystyrene-supported selenomethyl-sulfonates have been prepared from 1% cross-linked polystyrene resin. These novel reagents were treated with base to produce polystyrene-supported a-seleno carbanions, which reacted with alkyl halides, followed by stereospecific selenoxide syn-elimination to give 2i-vinylphosphonates and is-vinylsulfones respectively. And also these novel polymer reagents can be regenerated and reused.Thirdly, The preparation of 3-aryl-5-substituted (E)-ethenyl isoxazoles and l-isoxazolyl-2-isoxazolinyl substituted (E)-ethenes was developed through 1, 3-dipolar cycloaddition of nitrile oxides, α-alkylation reaction and(or) another 1, 3-dipolar cycloaddition of nitrile oxides based on polystyrene-supported propargyl selenide. The polystyrene-supported selenium resins used here not only facilitate separation of products, but also assist the crucial reaction of α-alkylation and selenoxide syn-elimination, which ensures the purity of the products: only the alkylated resin underwent selenoxide syn-elimination under mild cleavage conditions and no reaction was observed for the unalkylated resin under the same conditions.Fourthly, The preparation of 1 -triazolyl-2-isoxazolinyl substituted (E)-ethenes was developed through an one-pot 1, 3-dipolar cycloaddition of NaN₃ and RI, α-alkylation reaction of substituted allyl bromides and 1, 3-dipolar cycloaddition of nitrile oxidesbased on polystyrene-supported propargyl selenide. The polystyrene-supported selenium resins used here not only facilitate separation of products, but also assist the crucial reaction of a-alkylation and selenoxide syw-elimination, which ensures the purity of the products.Fifthly, The preparation of l-oxadiazolyl-2-isoxazolinyl substituted (ï¿¡)-ethenes was developed through an one-pot Porco's condensation, a-alkylation reaction of substituted allyl bromides and 1, 3-dipolar cycloadditions of nitrile oxides based on polystyrene-supported a-selenoacetic acid. The polystyrene-supported selenium resins used here not only facilitate separation of products, but also assist the crucial reaction of a-alkylation and selenoxide syw-elimination, which ensures the purity of the products.