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

Carbene-stabilized diborynes of the form LBBL (L = NHC or 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

Metallfreie intermolekulare C-H-Borylierung von N-Heterocyclen an B-B-Mehrfachbindungen

Carbenstabilisierte Diborine der Form LBBL (L=N-heterocyclisches Carben (NHC) oder cyclisches Alkyl(amino)carben (CAAC)) induzieren bei Raumtemperatur eine schnelle, ertragreiche, intermolekulare ortho-C-H-Borylierung an N-Heterocyclen. Ein einfaches Pyridyldiboren wird gebildet, wenn ein NHC-stabilisiertes Diborin mit Pyridin kombiniert wird, während ein CAAC-stabilisiertes Diborin zur Aktivierung von zwei Pyridinmolekülen führt, um ein tricyclisches Alkylidenboran zu bilden, das durch Erhitzen zu einem zwitterionischen, zweifach benzokondensierten 1,3,2,5-Diazadiborinin mittels einer weiteren H-Verschiebung umgelagert werden kann. Die Verwendung des verlängerten N-heteroaromatischen Chinolins führt unter milden Bedingungen über einen bisher unbekannten Bor-Kohlenstoff-Austauschprozess zu einem Borylmethylenboran

Suzuki-Miyaura Cross-Coupling of Bromotryptophan Derivatives at Ambient Temperature.

Dachwitz S, Duwe DH, Hong Wang Y, et al. Suzuki-Miyaura Cross-Coupling of Bromotryptophan Derivatives at Ambient Temperature. Chemistry - A European Journal. 2020;26(69):16357-16364.Mild reaction conditions are highly desirable for bio-orthogonal side chain derivatizations of amino acids, peptides or proteins due to the sensitivity of these substrates. Transition metal catalyzed cross-couplings such as Suzuki-Miyaura reactions are highly versatile, but usually require unfavourable reaction conditions, in particular, when applied with aryl bromides. Ligand-free solvent-stabilized Pd-nanoparticles represent an efficient and sustainable alternative to conventional phosphine-based catalysts, because the cross-coupling can be performed at considerably lower temperature. We report on the application of such a highly reactive heterogeneous catalyst for the Suzuki-Miyaura cross-coupling of brominated tryptophan derivatives. The solvent-stabilized Pd-nanoparticles are even more efficient than the literature-known ADHP-Pd precatalyst. Interestingly, the latter also leads to the formation of quasi-homogeneous Pd-nanoparticles as the catalytic species. One advantage of our approach is the compatibility with aqueous and aerobic conditions at near-ambient temperatures and short reaction times of only 2 hours. The influence of different N alpha -protecting groups, boronic acids as well as the impact of different amino acid side chains in bromotryptophan-containing peptides has been studied. Notably, a surprising acceleration of the catalysis was observed when palladium-coordinating side chains were present in proximal positions. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Hydrosilylation of B≡B triple bonds: catalyst- and reductant-free construction of B–Si bonds and B2Si heterocycles

Hydrosilanes undergo mild, uncatalyzed single and double 1,2-addition across the B–B triple bonds of diborynes, leading to an unsymmetrical silyldiborene and compounds with novel non-cluster three-membered B2Si rings. The reactions are a new addition to the very few catalyst- and alkali-metal-free methods available for the construction of B–Si bonds

Stepwise and selective synthesis of chelating, multimetallic and mixed-metal π-diborene complexes

The reaction of a pyridyl-substituted, doubly Lewis base-stabilised diborene with different amounts of copper(I) precursors led to the formation of the first chelating π-diborene complexes, the first π-diborene complexes in which metals are bound to both faces of the B=B bond, and the first mixed-metal π-diborene species