Solid-Phase Organic Synthesis Of Heterocyclic Compounds Containing Bromo Or Iodo Substituent Using Recyclable Polystyrene-Supported Selenium Bromide

In this dissertation, the application of polystyrene-supported selenium bromide reagent in solid-phase organic synthesis of heterocyclic compounds containing bromo or iodo substituent was investigated.Firstly, intramolecular electrophilic cyclization of 1 % cross-linked polystyrene-supported selenium bromide with ortho allylated phenols afforded 2-selenomethyl-2,3-dihydrobenzofuran resins, followed by treatment with bromine or methyl iodide and sodium iodide to yield 2-bromomethyl-2,3-dihydrobenzofurans and 2-iodomethyl-2,3-dihydrobenzofurans, respectively. Evident advantages of this method are mild reaction conditions, easy operation, odorlessness, good yields (83–95 %), and high purities (93–98 %) of products. The polystyrene-supported selenium bromide can be regenerated and used efficiently for recycle after simple treatment.Secondly, The lactonization reaction of pent-4-enoic acids with polystyrene-supported selenium bromide proceeded smoothly under mild reaction conditions with simple operation to afford 5-selenomethyl-γ-butyrolactone resins, followed by substitution cleavage of selenium resins with sodium iodide and methyl iodide to form 5-iodomethyl-γ-butyrolactones in with good yields (82–95 %) and high purities (92–95 %). The polystyrene-bound selenium bromide reagent can be also regenerated and reused to some extent. For theα-substituted pent-4-enoic acids, a mixture product of two diastereoisomers containing syn lactones as major isomer was obtained.Finally, reaction of selenium bromide resin with LiBH4 afforded the corresponding polystyrene-supported lithium selenide, which was treated with bromoacetic acid to form polymer-bound selenoacetic acid. The acylation of this selenium reagent with acid hydrazides was carried out smoothly in the presence of dicyclohexyl carbodiimide (DCC). Then the cyclocondensation reaction of the resulted hydrazide resin in reflux phosphorus oxychloride proceeded efficiently to produce 2-selenomethyl-1,2,4-triazole resins, which were further cleaved using substitution cleavage methods as above of selenium resins to furnish 2-bromomethyl or 2-iodomethyl substituted 1,2,4-triazole derivatives in 73–83 % yields with simple workup. The purity of crude products without further purification was above 90 %. The polystyrene-supported selenium bromide reagent can be regenerated and reused as environmentally benign reagent. The polystyrene-supported selenium bromide still showed good reactivity after being repeated four times in the same reaction.