A practicable synthesis of 2,3-disubstituted 1,4-dioxanes bearing a carbonyl functionality from α,β-unsaturated ketones using the Williamson strategy

In Situ Hypoiodite-Catalyzed Oxidative Rearrangement of Chalcones: Scope and Mechanistic Investigation

It is highly desirable to avoid using rare or toxic metals for oxidative reactions in the synthesis of pharmaceuticals and fine chemicals. Hypervalent iodine compounds are environmentally benign alternatives, but their catalytic use has been quite limited. Herein, the protocol for in situ hypoiodite-catalyzed oxidative rearrangement of chalcones is first realized under mild and metal-free conditions, which provided a nontoxic, environmental-benign, and catalytic alternative to the thallium-based protocol. Also, the applicability and effectiveness of this catalytic protocol got well demonstrated via gram-scale synthesis and product derivatization. What is more, control and NMR tracking experiments were performed to figure out the possible catalytic species and intermediates.

Selective Synthesis of 1,4-Dioxane from Oxirane Dimerization over ZrO2/TiO2 Catalyst at Low Temperature

We report a route to produce 1,4-dioxane from oxirane by using ZrO2/TiO2 as catalyst. The composite oxide ZrO2/TiO2 was prepared by a coprecipitation method and the catalytic performance was tested through the synthesis of 1,4-dioxane from oxirane in a pipe reactor. The X-ray diffraction (XRD) shows that ZrO2 and TiO2 are in crystal form. When the mass percentage of ZrO2 is 25%, the composite oxide ZrO2/TiO2 presents as an amorphous form. The sample 25%ZrO2/TiO2 exhibits a specific surface area of 269.5 m2·g−1 and pore volume of 1.34 mL·g−1. The catalyst has 670 µmol·g−1 of NH3-TPD acid, and the characterization of ammonia infrared spectroscopy (NH3-FTIR) shows that both Brønsted and Lewis acids are present on the surface of the catalyst. The reaction mechanism was analyzed according to the distribution of product. The test of catalytic performance showed 100.0% conversion of oxirane and 86.2% selectivity of 1,4-dioxane at the optimal operation conditions: atmospheric pressure, reaction temperature 75 °C and gaseous hourly space velocity of 1200.0 h−1. The catalyst exhibits good catalytic performance stability after continuous use for 720 h.