Metal-Free Intermolecular C-H Borylation of N-Heterocycles at B-B Multiple Bonds

Tobias Brückner; Benedikt Ritschel; J Oscar C Jiménez-Halla; Felipe Fantuzzi; Dario Duwe; Christian Markl; Rian D Dewhurst; Maximilian Dietz; Holger Braunschweig

doi:10.1002/anie.202213284

Metal-Free Intermolecular C-H Borylation of N-Heterocycles at B-B Multiple Bonds

Angew Chem Int Ed Engl. 2023 Jan 26;62(5):e202213284. doi: 10.1002/anie.202213284. Epub 2022 Dec 22.

Authors

Tobias Brückner^{1

2}, Benedikt Ritschel^{1

2}, J Oscar C Jiménez-Halla³, Felipe Fantuzzi⁴, Dario Duwe^{1

2}, Christian Markl^{1

2}, Rian D Dewhurst^{1

2}, Maximilian Dietz^{1

2}, Holger Braunschweig^{1

2}

Affiliations

¹ Institute for Inorganic Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
² Institute for Sustainable Chemistry & Catalysis with Boron, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
³ Department of Chemistry, Division of Natural and Exact, 36050, Guanajuato, Mexico.
⁴ School of Chemistry and Forensic Science, University of Kent, Park Wood Rd, Canterbury, CT2 7NH, UK.

Abstract

Carbene-stabilized diborynes of the form LBBL (L=N-heterocyclic carbene (NHC) or cyclic alkyl(amino)carbene (CAAC)) induce rapid, high yielding, intermolecular ortho-C-H borylation at N-heterocycles at room temperature. A simple pyridyldiborene is formed when an NHC-stabilized diboryne is combined with pyridine, while a CAAC-stabilized diboryne leads to activation of two pyridine molecules to give a tricyclic alkylideneborane, which can be forced to undergo a further H-shift resulting in a zwitterionic, doubly benzo-fused 1,3,2,5-diazadiborinine by heating. Use of the extended N-heteroaromatic quinoline leads to a borylmethyleneborane under mild conditions via an unprecedented boron-carbon exchange process.

Keywords: Boron; Borylation; Carbene; Diboryne; Hydroarylation.

Abstract

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