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

Abstract

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)/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.

Environmental Catalysis: Present and Future

“…From an environmental point of view, special attention has received the bening-by-design of biomassderived catalyst, including materials with specific properties for application such as electro-and photo-catalysis. [30][31][32] Biomass is a wide concept, which includes lignocellulosic materials, starch/ oilseed/sugar, aquatic cultures, and bio-derived wastes (agricultural/animal/anthropological residues). The pair biomass and Daily Rodríguez-Padró n is a PhD student at the Universidad de Cordoba (Group FQM-383).…”

Selective Synthesis of Primary Anilines from NH3 and Cyclohexanones by Utilizing Preferential Adsorption of Styrene on the Pd Nanoparticle Surface

“…[5] Additionally,this strategy is known to be effective for synthesizing arylamines other than primary anilines by the in situ condensation of amines with cyclohexanones and subsequent dehydrogenation of the imine or enamine intermediates. [6] As an application to the synthesis of primary anilines, the direct use of NH 3 is quite difficult, and thus Pd-catalyzed Semmler-Wolff-type reactions have been recently reported as the second best strategy; [7,8] our group has previously reported the in situ synthesis of cyclohexanone oximes from NH 2 OH and cyclohexanones,f ollowed by the conversion to primary anilines via dehydrogenation and NÀOb ond cleavage using supported Pd nanoparticle catalysts. [8] Since the direct use of NH 3 as an itrogen source in chemical synthesis is attractive from the viewpoints of step and atom economy, [9] thed evelopment of the direct conversion of NH 3 and cyclohexanones into primary anilines is an important task.…”

Selective Synthesis of Primary Anilines from NH3 and Cyclohexanones by Utilizing Preferential Adsorption of Styrene on the Pd Nanoparticle Surface

“…[5] Unlike the conventional synthetic approaches via aromatic CÀHb ond substitution, dehydrogenative aromatization has been proposed where sixmembered carbocyclic rings,r eadily available or easily derived by classical synthetic methods,c an be used to synthesize phenol derivatives with various substitution patterns. [6] As an application to the synthesis of primary anilines, the direct use of NH 3 is quite difficult, and thus Pd-catalyzed Semmler-Wolff-type reactions have been recently reported as the second best strategy; [7,8] our group has previously reported the in situ synthesis of cyclohexanone oximes from NH 2 OH and cyclohexanones,f ollowed by the conversion to primary anilines via dehydrogenation and NÀOb ond cleavage using supported Pd nanoparticle catalysts. [6] As an application to the synthesis of primary anilines, the direct use of NH 3 is quite difficult, and thus Pd-catalyzed Semmler-Wolff-type reactions have been recently reported as the second best strategy; [7,8] our group has previously reported the in situ synthesis of cyclohexanone oximes from NH 2 OH and cyclohexanones,f ollowed by the conversion to primary anilines via dehydrogenation and NÀOb ond cleavage using supported Pd nanoparticle catalysts.…”

“…[5] Additionally,this strategy is known to be effective for synthesizing arylamines other than primary anilines by the in situ condensation of amines with cyclohexanones and subsequent dehydrogenation of the imine or enamine intermediates. [8] Since the direct use of NH 3 as an itrogen source in chemical synthesis is attractive from the viewpoints of step and atom economy, [9] thed evelopment of the direct conversion of NH 3 and cyclohexanones into primary anilines is an important task. [8] Since the direct use of NH 3 as an itrogen source in chemical synthesis is attractive from the viewpoints of step and atom economy, [9] thed evelopment of the direct conversion of NH 3 and cyclohexanones into primary anilines is an important task.…”

“…[6] As an application to the synthesis of primary anilines, the direct use of NH 3 is quite difficult, and thus Pd-catalyzed Semmler-Wolff-type reactions have been recently reported as the second best strategy; [7,8] our group has previously reported the in situ synthesis of cyclohexanone oximes from NH 2 OH and cyclohexanones,f ollowed by the conversion to primary anilines via dehydrogenation and NÀOb ond cleavage using supported Pd nanoparticle catalysts. [10] However,c onsidering the results obtained for the dehydrogenative aromatization strategy [5] including our previous studies, [8,11,12] there is acritical issue in achieving the selective synthesis of primary anilines;i .e., the desired primary anilines are typically more reactive than NH 3 for the condensation with cyclohexanone substrates,r eadily affording the corresponding imines (i.e., N-cyclohexylidene-anilines) (step 2, Figure 1a). [10] However,c onsidering the results obtained for the dehydrogenative aromatization strategy [5] including our previous studies, [8,11,12] there is acritical issue in achieving the selective synthesis of primary anilines;i .e., the desired primary anilines are typically more reactive than NH 3 for the condensation with cyclohexanone substrates,r eadily affording the corresponding imines (i.e., N-cyclohexylidene-anilines) (step 2, Figure 1a).…”