1.Chan-Evans-Lam Amination of Boronic Acid Pinacol (BPin) Esters: Overcoming the Aryl Amine Problem.
Vantourout JC1, Law RP2, Isidro-Llobet A2, Atkinson SJ2, Watson AJ1. J Org Chem. 2016 Apr 18. [Epub ahead of print]
The Chan-Evans-Lam reaction is a valuable C-N bond forming process. However, aryl boronic acid pinacol (BPin) ester reagents can be difficult coupling partners that often deliver low yields, in particular in reactions with aryl amines. Herein, we report effective reaction conditions for the Chan-Evans-Lam amination of aryl BPin with alkyl and aryl amines. A mixed MeCN/EtOH solvent system was found to enable effective C-N bond formation using aryl amines while EtOH is not required for the coupling of alkyl amines.
2.Ni/Cu-Catalyzed Defluoroborylation of Fluoroarenes for Diverse C-F Bond Functionalizations.
Niwa T1, Ochiai H1, Watanabe Y1, Hosoya T1. J Am Chem Soc. 2015 Nov 18;137(45):14313-8. doi: 10.1021/jacs.5b10119. Epub 2015 Nov 3.
Ni/Cu-catalyzed transformation of fluoroarenes to arylboronic acid pinacol esters via C-F bond cleavage has been achieved. Further versatile derivatization of an arylboronic ester has allowed for the facile two-step conversion of a fluoroarene to diverse functionalized arenes, demonstrating the synthetic utility of the method.
3.Preparing (Multi)Fluoroarenes as Building Blocks for Synthesis: Nickel-Catalyzed Borylation of Polyfluoroarenes via C-F Bond Cleavage.
Zhou J1,2, Kuntze-Fechner MW2, Bertermann R2, Paul US2, Berthel JH2, Friedrich A2, Du Z1, Marder TB2, Radius U2. J Am Chem Soc. 2016 Apr 18. [Epub ahead of print]
The [Ni(IMes)2]-catalyzed transformation of fluoroarenes into arylboronic acid pinacol esters via C-F bond activation and transmetalation with bis(pinacolato)diboron (B2pin2) is reported. Various partially fluorinated arenes with different degrees of fluorination were converted into their corresponding boronate esters.
4.Synthetic Reactions Using Low-valent Titanium Reagents Derived from Ti(OR)4 or CpTiX3 (X = O-i-Pr or Cl) in the Presence of Me3 SiCl and Mg.
Okamoto S1. Chem Rec. 2016 Mar 10. doi: 10.1002/tcr.201500277. [Epub ahead of print]
In the presence of Me3 SiCl, Ti(OR)4 or CpTiX3 (X = O-i-Pr or Cl) is reduced by Mg powder in THF to gradually generate a specific low-valent titanium (LVT) species that mediates several synthetic reactions. The LVT-catalyzed C-O bond-cleaving reactions of allyl and propargyl ethers and esters generate parent alcohols and carboxylic acids, respectively. O-allyl and propargyl carbamates are also readily deprotected by the LVT to afford parent amines. In addition, the respective reductive N-S or O-S bond cleavage of sulfonamides or sulfonyl esters mediated by the LVT was developed as a novel facile deprotection method. The reagent catalyzes intra- and intermolecular alkyne or alkyne/nitrile cycloaddition to produce substituted benzenes and pyridines, while epoxides and oxetanes are reduced to alcohols via an LVT-mediated homolytic ring opening. The McMurry coupling of aryl aldehydes and ketones proceeds with the LVT under homogeneous and mild reaction conditions and is effective for the polymerization of aromatic dialdehydes, generating conjugated polymers.