Xiongjie Jin

Heterogeneously Catalyzed Efficient Hydration of Alkynes to Ketones by Tin–Tungsten Mixed Oxides

The Sn-W mixed oxide prepared by calcination of the Sn-W mixed hydroxide precursor with a Sn/W molar ratio of 2:1 at 800 °C (SnW2-800) acts as an efficient heterogeneous catalyst for the hydration of alkynes. Structurally diverse terminal and internal alkynes, including aromatic, aliphatic, and double-bond-containing ones, can be converted into the corresponding ketones in moderate to high yields. The catalytic activity of SnW2-800 is much higher than those of previously reported heterogeneous catalysts and commonly utilized acid catalysts. The observed catalysis was truly heterogeneous, and the retrieved catalyst can be reused at least three times with retention of its high catalytic performance. The reaction rate for the SnW2-800-catalyzed hydration was decreased by addition of 2,6-lutidine and the hydration hardly proceeded in the presence of an equimolar amount of this compound with respect to that of the Brønsted acid sites in SnW2-800. Therefore, the present hydration is mainly promoted by the Brønsted acid sites in SnW2-800.

Gold‐Catalyzed Heterogeneous Aerobic Dehydrogenative Amination of α,β‐Unsaturated Aldehydes to Enaminals

Although enaminals (β-enaminals) are very important compounds and have been utilized as useful synthons for various important compounds, they have been synthesized through non-green and/or limited procedures until now. Herein, we have successfully developed a green synthetic procedure using a heterogeneous catalyst. In the presence of gold nanoparticles supported on manganese-oxide-based octahedral molecular sieves OMS-2 (Au/OMS-2), dehydrogenative amination of α,β-unsaturated aldehydes with amines proceeded efficiently, with the corresponding enaminals isolated in moderate to high yields (50-97 %). The catalysis was truly heterogeneous, and Au/OMS-2 could be reused. Furthermore, the formal Wacker-type oxidation of α,β-unsaturated aldehydes to enaminones has been realized.

Copper-catalyzed oxidative cross-coupling of H-phosphonates and amides to N-acylphosphoramidates.

A simple combination of copper(II) acetate (Cu(OAc)(2)) and an appropriate base could promote oxidative cross-coupling of H-phosphonates and amides using air as a terminal oxidant. The substrate scope was broad with respect to both dialkyl H-phosphonates and nitrogen nucleophiles (including oxazolidinone, lactam, pyrrolidinone, urea, indole, and sulfonamide derivatives), giving the corresponding P-N coupling products in moderate to high yields.

Supported Gold Nanoparticles for Efficient α‐Oxygenation of Secondary and Tertiary Amines into Amides

Although the α-oxygenation of amines is a highly attractive method for the synthesis of amides, efficient catalysts suited to a wide range of secondary and tertiary alkyl amines using O2 as the terminal oxidant have no precedent. This report describes a novel, green α-oxygenation of a wide range of linear and cyclic secondary and tertiary amines mediated by gold nanoparticles supported on alumina (Au/Al2 O3 ). The observed catalysis was truly heterogeneous, and the catalyst could be reused. The present α-oxygenation utilizes O2 as the terminal oxidant and water as the oxygen atom source of amides. The method generates water as the only theoretical by-product, which highlights the environmentally benign nature of the present reaction. Additionally, the present α-oxygenation provides a convenient method for the synthesis of (18) O-labeled amides using H2 (18) O as the oxygen source.

Facile access to N-substituted anilines via dehydrogenative aromatization catalysis over supported gold–palladium bimetallic nanoparticles

N-Substituted anilines are widely utilized important compounds, and the development of their diverse synthetic procedures is of great significance. Herein, we have successfully developed a widely applicable powerful catalytic route to N-substituted anilines. In the presence of a gold–palladium alloy nanoparticle catalyst (Au–Pd/Al2O3) and styrene, various kinds of structurally diverse N-substituted anilines (twenty three examples) could be synthesized starting from cyclohexanones and amines (including aliphatic primary and secondary amines and anilines). The catalytic performance was strongly influenced by the nature of the catalyst. A supported gold catalyst (Au/Al2O3) was completely inactive for the present transformation. Although a supported palladium catalyst (Pd/Al2O3) gave the desired N-substituted anilines to some extent, the performance was inferior to that of Au–Pd/Al2O3. The catalytic activity of the palladium species in Au–Pd/Al2O3 was at least ca. three times higher than that in Pd/Al2O3. Moreover, the performance of Au–Pd/Al2O3 was superior to that of a physical mixture of Au/Al2O3 and Pd/Al2O3. Thus, palladium was intrinsically effective for the present transformation (dehydrogenative aromatization) and its performance was improved by alloying with gold. The present transformation proceeds through a sequence of the dehydrative condensation of cyclohexanones and amines to produce enamines (or ketimines), followed by the dehydrogenative aromatization to produce the corresponding N-substituted anilines. In the aromatization step, styrene could act as an effective hydrogen acceptor to selectively produce the desired N-substituted anilines without catalyzing the disproportionation of the enamine intermediates. The observed catalysis using Au–Pd/Al2O3 was truly heterogeneous in nature, and Au–Pd/Al2O3 could be reused.

Aerobic cross-dehydrogenative coupling of terminal alkynes and tertiary amines by a combined catalyst of Zn2+ and OMS-2

In the presence of ZnBr2 and a manganese oxide-based octahedral molecular sieve (OMS-2), cross-dehydrogenative coupling of a wide range of terminal alkynes and tertiary amines to propargylamines efficiently proceeded using molecular oxygen as the terminal oxidant.

Heterogeneously catalyzed self-condensation of primary amines to secondary amines by supported copper catalysts

Self-condensation of primary amines to symmetrically substituted secondary amines could efficiently be promoted by an inexpensive supported copper catalyst, Cu/Al2O3, easily prepared by the reduction of the hydroxide precursor, Cu(OH)x/Al2O3. Various kinds of structurally diverse primary amines including benzylamine, picolylamine, and aliphatic amine derivatives could selectively be converted into the corresponding secondary amines in moderate to excellent yields without any cocatalysts such as bases and stabilizing ligands in 1 atm of Ar or H2. The reactions in H2 showed higher selectivities to desired secondary amines than those in Ar. The roles of H2 are the promotion of hydrogenation of N-alkylimines and the stabilization of active Cu(0) species. In addition, in the presence of Cu/Al2O3, unsymmetrically substituted secondary amines could efficiently be synthesized by N-alkylation of primary amines with alcohols and reductive amination of aldehydes. The observed catalysis was truly heterogeneous, and the retrieved Cu/Al2O3 catalyst could be reused for self-condensation without a significant loss of its catalytic performance. The reaction mechanism involving dehydrogenation of primary amines and condensation to N-alkylimines followed by hydrogenation, the so-called “borrowing hydrogen pathway”, has been proposed.

Gold nanoparticles on OMS-2 for heterogeneously catalyzed aerobic oxidative α,β-dehydrogenation of β-heteroatom-substituted ketones

In the presence of Au nanoparticles supported on manganese oxide OMS-2 (Au/OMS-2), various kinds of β-heteroatom-substituted α,β-unsaturated ketones (heteroatom = N, O, S) can be synthesized through α,β-dehydrogenation of the corresponding saturated ketones using O2 (in air) as the oxidant. The catalysis of Au/OMS-2 is truly heterogeneous, and the catalyst can be reused.

Phosphovanadomolybdic acid catalyzed desulfurization–oxygenation of secondary and tertiary thioamides into amides using molecular oxygen as the terminal oxidant

In the presence of phosphovanadomolybdic acids, e.g., H6PV3Mo9O40, desulfurization–oxygenation of various kinds of structurally diverse secondary and tertiary thioamides proceeded efficiently using molecular oxygen as the terminal oxidant, affording the corresponding amides in moderate to excellent yields. In addition, 18O-labeled amides could readily be synthesized using H218O as the oxygen source.

Selective Synthesis of Primary Anilines from Cyclohexanone Oximes by the Concerted Catalysis of a Mg–Al Layered Double Hydroxide Supported Pd Catalyst

Although the selective conversion of cyclohexanone oximes to primary anilines would be a good complement to the classical synthetic methods for primary anilines, which utilize arenes as the starting materials, there have been no general and efficient methods for the conversion of cyclohexanone oximes to primary anilines until now. In this study, we have successfully realized the efficient conversion of cyclohexanone oximes to primary anilines by utilizing a Mg-Al layered double hydroxide supported Pd catalyst (Pd(OH)x/LDH) under ligand-, additive-, and hydrogen-acceptor-free conditions. The substrate scope was very broad with respect to both cyclohexanone oximes and cyclohexenone oximes, which gave the corresponding primary anilines in high yields with high selectivities (17 examples, 75% to >99% yields). The reaction could be scaled up (gram-scale) with a reduced amount of the catalyst (0.2 mol %). Furthermore, the one-pot synthesis of primary anilines directly from cyclohexanones and hydroxylamine was also successful (five examples, 66-99% yields). The catalysis was intrinsically heterogeneous, and the catalyst could be reused for the conversion of cyclohexanone oxime to aniline at least five times with keeping its high catalytic performance. Kinetic studies and several control experiments showed that the high activity and selectivity of the present catalyst system were attributed to the concerted catalysis of the basic LDH support and the active Pd species on LDH. The present transformation of cyclohexanone oximes to primary anilines proceeds through a dehydration/dehydrogenation sequence, and herein the plausible reaction mechanism is proposed on the basis of several pieces of experimental evidence.