ABSTRACT
Ir catalysts supported by bidentate silyl ligands that contain P- or N-donors are shown to effect ortho borylations for a range of substituted aromatics. The substrate scope is broad, and the modular ligand synthesis allows for flexible catalyst design.
Subject(s)
Boron Compounds/chemical synthesis , Chelating Agents/chemical synthesis , Coordination Complexes/chemistry , Nitrogen/chemistry , Organophosphorus Compounds/chemical synthesis , Organosilicon Compounds/chemical synthesis , Boron Compounds/chemistry , Catalysis , Chelating Agents/chemistry , Iridium/chemistry , Molecular Structure , Organophosphorus Compounds/chemistry , Organosilicon Compounds/chemistryABSTRACT
Molecules labeled with fluorine-18 are used as radiotracers for positron emission tomography. An important challenge is the labeling of arenes not amenable to aromatic nucleophilic substitution (SNAr) with [(18)F]F(-). In the ideal case, the (18)Fâ fluorination of these substrates would be performed through reaction of [(18)F]KF with shelf-stable readily available precursors using a broadly applicable method suitable for automation. Herein, we describe the realization of these requirements with the production of (18)Fâ arenes from pinacol-derived aryl boronic esters (arylBPin) upon treatment with [(18)F]KF/K222 and [Cu(OTf)2(py)4] (OTf = trifluoromethanesulfonate, py = pyridine). This method tolerates electron-poor and electron-rich arenes and various functional groups, and allows access to 6-[(18)F]fluoro-L-DOPA, 6-[(18)F]fluoro-m-tyrosine, and the translocator protein (TSPO) PET ligand [(18)F]DAA1106.
Subject(s)
Copper/chemistry , Fluorine Radioisotopes/chemistry , Halogenation/physiology , Positron-Emission Tomography/methods , Molecular StructureABSTRACT
Not a trace: Borylation of the nitrogen in nitrogen heterocycles or anilines provides a traceless directing group for subsequent catalytic C-H borylation. Selectivities that previously required Boc protection can be achieved; furthermore, the NBpin directing group can be installed and removed in-situ, and product yields are substantially higher. Boc=tert-butoxycarbonyl, pin=pinacolato.
Subject(s)
Aniline Compounds/chemistry , Boron Compounds/chemical synthesis , Boron Compounds/chemistry , Catalysis , Indoles/chemistry , Pyrroles/chemistryABSTRACT
With the aid of high-throughput screening, the efficiency of Ir-catalyzed C-H borylations has been assessed as functions of precatalyst, boron reagent, ligand, order of addition, temperature, solvent, and substrate. This study not only validated some accepted practices but also uncovered unconventional conditions that were key to substrate performance. We anticipate that insights drawn from these findings will be used to design reaction conditions for substrates whose borylations are difficult to impossible using standard catalytic conditions.
Subject(s)
Boron Compounds/chemical synthesis , High-Throughput Screening Assays , Iridium/chemistry , Organometallic Compounds/chemistry , Boron Compounds/chemistry , Catalysis , Molecular StructureABSTRACT
Experiment and theory favour a model of C-H borylation where significant proton transfer character exists in the transition state.
