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The Tertiary Organometallic Reagent Promoted Reductive Coupling of Aryl Halides
Published in John R. Kosak, Thomas A. Johnson, Catalysis of Organic Reactions, 2020
The synthesis of biaryl products from aryl halides continues to draw attention from both academic and industrial investigators as these compounds have found applications in wide variety of pharmaceuticals and specialty chemicals. Recent publications in the patent literature have demonstrated a new use for substituted biaryls as precursors for phosphine ligands utilized in transition metal catalyzed processes. The unique ligand, 2,2′-bis(diphenylphosphino-methyl)-1,1′-biphenyl, commonly referred to as BISBI, can be prepared from 2,2′-dimethyl-1,1’-biphenyl by preparation of the dianion [1] of the biaryl and subsequent reaction with chlorodiphenylphosphine (Eq. 1). BISBI, in combination with rhodium has been shown to serve as an effective hydroformylation catalyst [2] which is capable of producing aldehyde products with a normal-to-branched product ratio of greater that 30 to 1 (Eq. 2).
General Princlpes
Published in Martin B., S.Z., of Industrial Hygiene, 2018
Organohalide compounds have halogen-substituted hydrocarbon molecules. This means that each compound has fluorine, chloride, bromine, or iodine atoms in its structure. Alkyl halides in this group include dichlo-romethane (found in paint strippers), carbon tetrachloride (refrigerants), and 1,2-dibromoethane (an insecticide). The alkenyl or olefinic organohalides include: vinyl chloride (used to produce polyvinyl chloride, PVC), a known carcinogen, trichlorethylene (used for degreasing and as a drycleaning solvent), tetrachloroethylene, and hexachlorobutadiene (used as a hydraulic fluid). Aryl halides are used in chemical synthesis and as pesticides and solvents. They are derivatives of benzene and toluene. Polychlorinated bi-phenyls (PCBs), highly toxic materials, are an example of a halogenated biphenyl. Chlorofluorocarbons (CFCs), halons, and hydrogen-containing chlorofluorocarbons are of significant importance to the environment. CFCs, once used primarily as refrigerants and aerosol propellents, are believed to have caused the breakdown of the ozone layer and have been banned from production. Halogens used in fire extinguishers as halon have also been implicated in the depletion of the ozone layer and are being phased out. Hydrogen containing chlorofluorocarbons (HFCs) are being touted as the substitute for CFCs as refrigerants and plastic foam blowing agents. Chlorinated phenyls such as pentachlorophenol, are used to treat wood against fungi and insect infestation. The byproduct of that process causes hazardous waste, which has been known to cause liver damage and dermatitis.
Benzene, Aromaticity, and Benzene Derivatives
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Aryl halides are benzene derivatives, Ar–X, where the X group is Cl, Br, I, and sometimes F. Aryl halides are common reaction partners in nucleophilic reactions of benzene derivatives.Can a nucleophile displace halogen of an aryl halide in a substitution reaction?
Copper-assisted synthesis of five-membered O-heterocycles
Published in Inorganic and Nano-Metal Chemistry, 2020
Navjeet Kaur, Yamini Verma, Neha Ahlawat, Pooja Grewal, Pranshu Bhardwaj, Nirmala Kumari Jangid
Glorius and Altenhoff[168] reported this two-component protocol where o-haloacetanilide precursor was produced in situ by a domino intramolecular carbon–oxygen and intermolecular carbon–nitrogen bond-forming process with Cu catalyst to transform primary amide into benzoxazoles directly (Scheme 74). A highly regioselective reaction was developed with judicious choice of o-dihaloarene precursor. On the contrary to tandem reaction initiated by single C–X coupling in the presence of copper catalyst, reactions that involved double C–X coupling were more manipulable theoretically because the consistency of reactions conditions were favored by different C–X coupling transformations. These reactions were designed employing o-dihaloarenes to introduce proper nucleophiles twice. The limited use of this protocol was due to scarce availability of o-halogenated aryl halides or analogous reactants. Glorius and coworkers[172] synthesized benzoxazoles by copper-catalyzed tandem reaction primary amides and dihalobenzenes. The reaction involved a carbon–nitrogen coupling and a carbon-oxygen coupling. Halo atoms Br, Cl, I all were applicable in these reactions, while when both X1 and X2 were chloride no product was formed. This approach was then extended to vinyl 1,2-bromides and primary amides to afford oxazoles products via a double coupling tandem process.[30,98]