From homogeneous to heterogeneous catalysis of the three-component coupling of oxysulfonyl azides, alkynes, and amines

A reliable procedure for the synthesis of oxysulfonyl azides has been developed and applied to the three-component coupling reactions of azides, alkynes, and amines catalyzed homogeneously by CuI, which led to the formation of N-oxysulfonyl amidines with good yields. To fully evaluate the catalytic activity towards this coupling reaction, two coordination frameworks, namely, Cu₂I₂(PDIN) without micropores and Cu₂I₂(BTTP4) with micropores (PDIN=1,4-phenylene diisonicotinate, BTTP4=benzene-1,3,5-triyltriisonicotinate), were prepared by a facile one-pot reaction as heterogeneous catalysts. Catalytic results showed that nonporous Cu₂I₂(PDIN) was almost inactive for the three-component coupling reaction, whereas microporous Cu₂I₂(BTTP4) was an efficient heterogeneous catalyst for the synthesis of N-oxysulfonyl amidines. Furthermore, porous Cu₂I₂(BTTP4) displayed a shape-selective performance with respect to the alkyne substrates, and aromatic alkynes were preferable to aliphatic alkynes. The location of the catalytically active sites in the Cu₂I₂(BTTP4) framework has been studied by a series physical techniques, which includes powder XRD, CO₂ gas adsorption, IR spectroscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy, which suggests that the catalytic sites are not only on the external surface but also inside the micropores. Azide-ways manoeuver: Oxysulfonyl azide is developed for the formation of N-oxysulfonyl amidines. Three kinds of Cu^I catalysts are tested, which include CuI, Cu₂I₂(PDIN) without micropores, and Cu₂I₂(BTTP4) with micropores (PDIN=1,4-phenylene diisonicotinate, BTTP4=benzene-1,3,5-triyltriisonicotinate). Both homogeneous CuI and heterogeneous Cu₂I₂(BTTP4) are catalytically efficient and provide N-oxysulfonyl amidines in good yields.