Tertiary Amine Functionalized Polyacrylonitrile Fiber Catalyst For The Synthesis Of Tetrahydrothiophenes

Organic homogeneous catalysts are very important in chemistry due to theirwidely useage in organic synthesis and asymmetric synthesis. But these homogeneouscatalysts have the disadvantages of complicated post-treatment, difficult separationprocesses, troublesome recovery of the catalysts, and severe pollution to theenvironment. Immobilized catalyst attract researchers’ great attentions in recent yearsdue to their good performance on reusability, highier selectivity to the reaction, easilypost-treatment, and environmentally friendly.In this research, a new tertiary amine functionalized polyacrylonitrile fibercatalyst was prepared: commercially available polyacryonitrile fiber was refluxed inan ethylenediamine aqueous solution to produce the ethylenediamine aminated fiber(PANEF). Then, under the alkaline condition, PANEF reacted with3-dimethylaminopropylchloride hydrochloride to produce PANTF. The best reactionconditions were found by optimizing the amounts of reactants, reaction time, reactiontemperature and the pH value of the system. The produced fiber catalyst wascharacterized by elemental analysis, scanning electron microscopy (SEM) andfourier-transfer infrared spectroscopy (FTIR).And then PANTF was used to catalyze tandem Michael-intramolecular Henryreactions between1,4-dithiane-2,5-diol and trans-β-nitrostyrenes to form thecorresponding tetrahydrothiophene derivatives. This newly developed fiber catalyst isapplicable to a wide range of trans-β-nitroalkenes and affords good to excellent yieldsunder mild conditions (with2.5mol%fiber catalyst at50oC in ethanol for5h). Thefiber catalyst exhibits excellent recyclability and reusability (up to10times) aftersimple workup procedure with only a slight loss in catalytic activity. It is noteworthythat the major diastereomers have r-R, trans-nitro, trans-hydroxy configurationswith diastereoselectivities of up to15:1. These make the PANTF a bright prospect inthe application.All the synthesized substrates were characterized by1H NMR, and all the targetcompounds were characterized by1H NMR and13C NMR, all the new compoundswere further confirmed by HRMS and IR.