Preparation Of Polystyrene-Supported Organoselenium Reagents And Their Applications In The Synthesis Of Heterocyclic Compounds

In this dissertation,the preparation of polystyrene-supported organoselenium compounds and their applications in the synthesis of heterocyclic compounds were investigated.Firstly,polystyrene-supportedα-selanyl-acrylic acid ethyl ester has been prepared from 1%cross-linked polystyrene resin.This novel reagent reacted with nitrile oxides,azide,cyclopentadiene,furan and isoprene respectively,followed by stereospecific syn-elimination of selenoxide to give 3,5-disubstituted isoxazoles and 1,2,3-triazoles,1,3-and 1,4-cyclo-diene derivatives.Secondly,polystyrene-supportedα-selanyl-acrylic acid has been prepared from 1%cross-linked polystyrene resin.The novel reagent reacted with amidoxime through an one-pot Porco's condensation to give resin-bound 3-substituted-5-vinyl-1,2,4-oxadiazole initially,which then reacted with nitrite oxides and azides through a 1,3-dipolar cycloaddition,or reacted with cyclopentadiene and isoprene to furnish the resin-bound biheteroaryl.Finally,a linked heterocycle library of isoxazoles, 1,2,3-triazoles,bicyclo[2.2.1]hepta-2,5-diene or 4-methylcyclohexa -1,3-diene and 1,2,4-oxadiazoles was prepared by selenoxide syn-elimination of the resin-bound biheteroaryl.Thirdly,ethylβ-phenylselanyl-propionate has been synthesized from diphenyl diselenide.Vinyl substituted oxadiazoles and triazoles were obtained from selenoxide syn-elimination of phenylselanylethyl substituted oxadiazoles and triazoles,which were prepared through hydrazinolysis,acylation and cyclocondensation reactions of phenylselanyl propionate.Here,it is emphasized that the vinyl substituted heterocycles have a high reactive terminal double bond and are easy polymerized because the double bond is directly connected with an electronic withdrawing group. Hence,we used the phenylselanyl group to mask a vinylic functionality during this reaction.The protection of terminal double bond by phenylselanyl group was critical to the success of the reactions. Fifthly,resin-bound ethyl propionate was prepared by polystyrene-supported selenenyl bromide.The resin was hydrolyzed to give resin-bound propionic acid, which reacted with amidoxime through an one-pot Porco's condensation to give resin-bound substituted 1,2,4-oxadiazoles,followed by selenoxide syn-elimination of the resin.In all these reactions,the polystyrene-supported resins not only facilitate separation of products,but also serve as a pro-vinyl safety-catch linker,the syn-elimination of selenoxide in the last step realized both the release of heterocyclic compounds from the resin and the deprotection of the double bond.