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Direct (Hetero)Arylation Polymerization for the Preparation of Conjugated Polymers
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
J. Terence Blaskovits, Mario Leclerc
One report demonstrated the use of a ruthenium catalyst (with the (cymene)ruthenium dichloride dimer as precatalyst) for the copolymerization of pyrrole with dibromofluorene (Figure 5.24).178 Cα–H bond activation and arylation was guided by the use of an N-substituted 2-pyrimidinyl directing group on the pyrrole monomer, in which the heteroatoms of the pyrimidinyl group served as ligands for the metal center. The role of the directing group was confirmed by the attempt to polymerize a pyrrole in which the 2-pyrimidinyl moiety was replaced with a phenyl group, which led to a largely insoluble product. This was likely due to unselective couplings on pyrrole. The directing group was removed post-polymerization with a strong base at high temperature, adding another step to the preparation of the final material. The use of directing groups to guide C–H bond activation is widely used in direct arylation of small molecules (particularly in the early studies of intramolecular arylation), but to date this is the only example of the engineering of a substrate directing group with the purpose of guiding polymerization site-selectivity.
Synthesis Plan Analysis
Published in John Andraos, Synthesis Green Metrics, 2018
Plans C, D, and E are direct syntheses of the (+)-amine that involve stereoselective hydrogenation of acetophenone or its imine or hydrazone derivative. In Plan C, the chiral alcohol obtained from hydrogenation is subjected to tandem substitutions via the chloride and azide, and a final reduction. In Plans D and E, an imine or hydrazone derivative of acetophenone is prepared either having a chiral directing group attached (Plan E) or achiral group (Plan D). In Plan E, the subsequent reduction is a rhuthenium catalyzed transfer hydrogenation, which is followed by methanolysis of the chiral directing group. In Plan D, the hydrogenation step requires a chiral ligand attached to the rhodium catalyst which is then followed by reduction of the hydrazone with samarium diiodide.
Catalysis with Selenium and Sulfur
Published in Andrew M. Harned, Nonnitrogenous Organocatalysis, 2017
The ability to introduce chirality on the sulfur atom is a defining feature of sulfinamide catalysts. In contrast, other sulfur-based organocatalysts relied on one or more stereocenters located on other atoms to induce enantioselectivity. Following their earlier work on N-sulfinyl urea catalysis,68 Ellman and coworkers recently expanded the reaction scope to cover the addition of cyclohexyl Meldrum’s acid 116 to nitroalkenes 115 using low catalyst loadings (0.2–3 mol%).69 The reaction catalyzed by N-sulfinyl urea 114 is shown in Scheme 5.28. In these reactions, the sulfinyl group functioned as a chiral directing group and as an electron-withdrawing substituent. More detailed investigation, however, revealed that the chirality of the diamine moiety of the catalyst did not have a major impact on the enantioselectivity—the N-sulfinyl group exerted the dominant stereocontrolling effect. This paved the way to the development of a N-sulfinyl catalyst 118 that is chiral solely at the sulfur atom and capable of promoting the addition of α-substituted Meldrum’s acids 120 to nitroalkenes 119 (Scheme 5.29).70 Other N-sulfinyl amide-catalyzed enantioselective reactions developed recently by the group include an intermolecular aldol reaction71 and addition of thioacetic acid to nitroalkenes.72
Solution processible Co(III) quinoline-thiosemicarbazone complexes: synthesis, structure extension, and Langmuir-Blodgett deposition studies
Published in Journal of Coordination Chemistry, 2021
Robert J. Laverick, Ningjin Zhang, Eleanor Reid, Jaehwan Kim, Kelly J. Kilpin, Jonathan A. Kitchen
The molecular structures of L2H – L7H revealed the thiourea moiety adopted an anti-conformation and the imine bond adopted a trans arrangement. Regardless of the structure directing group, the ligand core containing the metal-binding pocket remained relatively planar with respect to the binding pocket (mean plane 2.73 − 12.01°), whereas the structure directing group was twisted relative to the metal binding pocket (mean plane 12.30 − 57.79°). As an example, Figure 2 shows the molecular structure of L6H·½MeOH (see Supporting Information for the remaining ligands). Pleasingly, the orientation of the structure directing group away from the metal-binding core leaves it free to participate in various supramolecular interactions (dependent on the functionality present) and dictate long range ordering within the material. It is this ordering that is important for many supramolecular materials-based applications, and indeed if the structure extending interactions are also observed in the metal complexes, we will have access to large families of metal-containing building blocks that can be assembled into larger, more complex architectures.
Transition-metal-catalyzed C–N cross-coupling reactions of N-unsubstituted sulfoximines: a review
Published in Journal of Sulfur Chemistry, 2018
Akram Hosseinian, Leila Zare Fekri, Aazam Monfared, Esmail Vessally, Mohammad Nikpassand
Interestingly, in the presence of [{RuCl2(p-cymene)}2]/AgSbF6/Ag2O as a catalytic system, the sulfoximine moiety acts as a strong directing group in ortho-arylation reactions. Thus, under these reaction conditions, the reaction of S-aryl-sulfoximine 62 with aryl boronic acids 63 afforded moderate to good yields of corresponding ortho-di-arylated sulfoximines 64 without any N-arylated products (Scheme 25) [13–15].