Amidation of Aryl Chlorides Using a Microwave-Assisted, Copper-Catalyzed Concurrent Tandem Catalytic Methodology

Crystal structures of N-[4-(trifluoromethyl)phenyl]benzamide and N-(4-methoxyphenyl)benzamide at 173 K: a study of the energetics of conformational changes due to crystal packing

The conformations of two aryl amides have been determined experimentally in crystal structures using X-ray data and calculated with DFT methods for the isolated mol­ecules. Geometrical comparisons are made along with energy analyses of the inter­molecular inter­actions in the two crystal structures.

As a part of our study of the syntheses of aryl amides, the crystal structures of two benzamides were determined from single-crystal X-ray data at 173 K. Both crystal structures contain mol­ecular units as asymmetric units with no solvent in the unit cells. Crystal structure I, TFMP, is the result of the crystallization of N-[4-(tri­fluoro­meth­yl)phen­yl]benzamide, C₁₄H₁₀F₃NO. Crystal structure II, MOP, is composed of N-(4-meth­oxy­phen­yl)benzamide, C₁₄H₁₃NO₂, units. TFMP is triclinic, space group P, consisting of two mol­ecules in the unit cell related by the center of symmetry. MOP is monoclinic, space group P2₁/c, consisting of four mol­ecules in the unit cell. Both types of mol­ecules contain three planar regions; a phenyl ring, an amide planar region, and a para-substituted phenyl ring. The orientations of these planar regions within the asymmetric units are compared to their predicted orientations, in isolation, from DFT calculations. The aryl rings are tilted approximately 60° with respect to each other in both experimentally determined structures, as compared to 30° in the DFT results. These conformational changes result in more favorable environments for N—H⋯O hydrogen bonding and aryl ring π-stacking in the crystal structures. Inter­molecular inter­actions were examined by Hirshfeld surface analysis and qu­anti­fied by calculating mol­ecular inter­action energies. The results of this study demonstrate that both hydrogen bonding and dispersion are essential to the side-by-side stacking of mol­ecular units in these crystal structures. Weaker dispersion inter­actions along the axial directions of the mol­ecules reveal insight into the melting mechanisms of these crystals.

C-H Amidation and Amination of Arenes and Heteroarenes with Amide and Amine using Cu-MnO as a Reusable Catalyst under Mild Conditions

An atom-economical and efficient route for the direct amidation and amination of aryl C-H bonds using our synthesized recyclable heterogeneous Cu-MnO catalyst is reported here. The direct C-H amidation was carried out using a simple amide without any preactivated coupling partner, and simple air was used as the sole oxidant. The reaction proceeds very smoothly with a broad range of substrates containing numerous functional groups in very good to excellent yields. Direct C-H aminations with a secondary amine were carried out under base-, ligand-, and external oxidant-free conditions in very good to excellent yields in very mild conditions. Both the amidation and amination can be scaled up on a gram scale with similar yields. The major advantage is that our catalyst is recyclable and reused several times without any significant loss of reactivity.

Recent Advances in Microwave-Assisted Copper-Catalyzed Cross-Coupling Reactions

Cross-coupling reactions furnishing carbon–carbon (C–C) and carbon–heteroatom (C–X) bond is one of the most challenging tasks in organic syntheses. The early developed reaction protocols by Ullmann, Ullman–Goldberg, Cadiot–Chodkiewicz, Castro–Stephens, and Corey–House, utilizing elemental copper or its salts as catalyst have, for decades, attracted and inspired scientists. However, these reactions were suffering from the range of functional groups tolerated as well as severely restricted by the harsh reaction conditions often required high temperatures (150–200 °C) for extended reaction time. Enormous efforts have been paid to develop and achieve more sustainable reaction conditions by applying the microwave irradiation. The use of controlled microwave heating dramatically reduces the time required and therefore resulting in increase in the yield as well as the efficiency of the reaction. This review is mainly focuses on the recent advances and applications of copper catalyzed cross-coupling generation of carbon–carbon and carbon–heteroatom bond under microwave technology.