Catalytic activity of new heteroleptic [Cu(PPh3)2(β-oxodithioester)] complexes: click derived triazolyl glycoconjugates

Abstract

A series of four new and two known luminescent heteroleptic Cu(I) complexes of the form [Cu(PPh₃)₂(β-oxodithioester)] (β-oxodithioester = methyl-3-hydroxy-3-(2-furyl)-2-propenedithioate L1 1, methyl-3-hydroxy-3-(2-thienyl)-2-propenedithioate L2 2, methyl-3-hydroxy-3-(4-methoxyphenyl)-2-propenedithioate L3 3, methyl-3-hydroxy-3-(4-bromophenyl)-2-propenedithioate L4 4, methyl-3-hydroxy-3-benzyl-2-propenedithioate L5 5 and methyl-3-hydroxy-3-(3-pyridyl)-2-propenedithioate, L6 6) have been synthesized and characterized by elemental (C, H, N) analysis, and IR, UV-visible, ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy and their structures have been ascertained by X-ray crystallography. These complexes were exploited as catalysts for azide–alkyne cycloaddition reactions (click chemistry) for the synthesis of triazolyl glycoconjugates, where they displayed efficient catalytic activity at room temperature. Optimization of the reaction conditions and formation of regioselective products in high yields in the absence of a base/additive are concomitant with the click protocol. The substrate scope was successfully extended by varying the types of sugar azides and alkyne scaffolds, affording the corresponding triazole products in excellent yields at low catalyst loadings (1 mol%). Furthermore, catalyst 1 showed excellent recyclability and was reused for five cycles with little decrease in efficiency.