Regioselective Ring-Opening of Spiro-Epoxyoxindoles by a Dual-Ligand Zinc-Based Metal–Organic Framework as an Efficient Heterogeneous Catalyst

Developing a heterogeneous catalyst for alcoholysis/hydrolysis of spiro-epoxyoxindoles to form β-alkoxy/β-hydroxy alcohols is an emerging and promising research area in the academia and industry due to its importance in the pharmaceutical industry. In this work, a chiral-phase pure Zn-based metal–organic framework (MOF), {[Zn2(D-CAM)2(L)]·MeOH·2H2O}n (ADES-6), has been constructed from mixed organic ligands involving D(+)-camphoric acid (D-H2CAM) and an amide-functionalized N-donor ligand ((E)-N′-(pyridin-4-ylmethylene)isonicotinohydrazide (L)) through versatile synthetic modes and characterized by different analytical techniques along with single-crystal X-ray diffraction (SXRD) analysis. The catalytic activity reveals that the prepared ADES-6 MOF could be exploited as a heterogeneous catalyst for regioselective ring-opening of different spiro-epoxyoxindoles to form β-alkoxy/β-hydroxy/β-chloro alcohols efficiently in the presence of appropriate nucleophiles. Furthermore, ADES-6 displays excellent activity for diverse substrates and can be reused in at least five successive cycles without significant reduction in activity. Mechanistic explorations indicate that the high efficiency of ADES-6 is attributed to the presence of a vacant Lewis acidic metal center, and an amide group of the ligand L in the framework as a Lewis basic site can synergistically activate the catalytic reaction. Importantly, ADES-6 behaved as one of the rare first main-group MOF-based catalysts reported in the ring-opening of spiro-epoxyoxindoles efficiently and few catalytic products are validated unambiguously by SXRD analysis.