Quinolinium modified β-cyclodextrin: An ionic ligand towards sustainable A3-coupling and tandem cyclisation reactions of aldehydes, amines and alkynes

An ionic Cu(I) complex (Cu(I)@Qun-beta-CD), stabilized by water soluble quinolinium modified beta-cyclodextrin (Qun-beta-CD) with an 8-N-pentyl side chain, was prepared and characterized by ESI-Mass, NMR and UV-Visible spectroscopies and also molecular modeling studies. The synthesized Cu(I)@Qun-beta-CD was found to be highly efficient in promoting A(3)-coupling reaction of various aldehydes, amines and terminal alkynes to yield propargylamines in acetonitrile medium. The prepared Qun-beta-CD (C) alone, without any metal ion, follows a different course exhibiting excellent catalytic efficiency in an intramolecular tandem cyclisation reaction of the same reagents to yield quinolines in aqueous medium. From the point of the environmental concerns, the work presented here has the merits of both three-component reaction, environmentally friendliness, easy separation, simple work-up, good yields, the avoidance of organic solvents and use of an inexpensive catalyst. The catalyst was recycled more than five consecutive cycles without any significant loss in its activity in both reactions.

Automated summary

The synthesized Cu(I)@Qun-beta-CD showed efficient catalytic activity in promoting A(3)-coupling reaction of various aldehydes, amines, and terminal alkynes in acetonitrile medium. The prepared Qun-beta-CD (C) alone exhibited excellent catalytic efficiency in an intramolecular tandem cyclisation reaction in an aqueous medium. The catalyst has the advantages of a three-component reaction, environmental friendliness, easy separation, good yields, avoidance of organic solvents, and reuse for multiple cycles.