Neue Substrate für Palladium‐katalysierte Kupplungsreaktionen von Aromaten

Abstract

Aromaten und Heteroaromaten sind allgegenwärtige Strukturelemente in Wirkstoffen und neuen Materialien. Die Funktionalisierung (“Veredelung”) von einfachen aromatischen Vorstufen ist deshalb nach wie vor von zentraler Bedeutung für die präparative Organische Chemie. In den letzten 20 Jahren haben vor allem Übergangsmetall‐katalysierte Kreuzkupplungen von Arylhalogeniden und ‐triflaten der Aromatenchemie neue Impulse gegeben, vor wenigen Jahren wurden auch erste technische Anwendungen realisiert. Seit kurzem ergänzen nun Carbonsäurederivate wie Anhydride und Ester das Substratspektrum derartiger Kupplungsreaktionen. Einige aktuelle Entwicklungen auf diesem Gebiet werden in diesem Aufsatz vorgestellt.

Palladium‐Catalyzed Intramolecular Decarboxylative Coupling of Arene Carboxylic Acids/Esters with Aryl Bromides

“…The residue was purified by column chromatography (ethyl acetate/petroleum ether), yielding 2 a (96 %) as a yellow oil. 1 H NMR (400 MHz, CDCl3) d = 5.02 (s, 2 H), 6.91 (dd, J = 8.1, 1.2 Hz, 1 H), 6.96 (dt, J = 7.5, 1.2 Hz, 1 H), 7.05 (d, J = 7.4 Hz, 1 H), 7.12-7.20 (m, 2 H), 7.28 (t, J = 7.6 Hz, 1 H), 7.60 (d, J = 7.7 Hz, 1 H), 7.64 ppm (dd, J = 7.7, 1.6 Hz, 1 H); IR (KBr): ñ = 3179, 1484, 1400, 1244, 1120, 1017, 755, 688 cm À1 ; MS (EI): m/z: 182 [M] + , 181, 152, 127, 115, 91, 76.…”

“…This process can provide unconventional alternatives to perform various types of C À C and C À heteroatom bond-forming reactions relative to typical organometallic reagents. [1] It is known that transition-metal-catalyzed cross-coupling reactions with organometallic reagents as coupling partners for the formation of unsymmetrical biaryl compounds, such as the Suzuki-Miyaura coupling reaction [Eq. ( 1)], have proven to be versatile and powerful methods.…”

“…(2)]. [1] Carboxylic acids are desirable cross-coupling partners owing to their prevalence in nature, ease of handling relative to organometallic reagents, high regioselectivity at the carboxylic acid position relative to that of CÀH functionalization, [3, 10c, 11] and the generation of CO 2 as the waste prod-uct. Since Nilsson reported the first example of transitionmetal-mediated decarboxylative biaryl coupling, [4] breakthroughs have been achieved by the groups of Goossen, [5] Myers, [6] and others [7][8][9][10][11] in the development of decarboxylative cross-coupling reactions.…”

Twisted Amides: From Obscurity to Broadly Useful Transition‐Metal‐Catalyzed Reactions by N−C Amide Bond Activation

“…N-glutarimide amides have been successfully utilized in two reaction manifolds:i )acyl-cross-coupling; [67] ii)decarbonylative cross-coupling. [68] In all reported examples, N-glutarimides un-derwentN ÀCa ctivation under milderc onditions than other amide substrates under given conditions.…”

Chemoselective Carbon‐Carbon Cross‐Coupling via Palladium‐Catalyzed Copper‐Mediated CS Cleavage of Disulfides

“…For example, aryl halides are not always easily available. Thus, the search for alternative electrophiles as novel substrates to organic halides for the cross‐coupling reactions has been the focus of much attention 4a. Among these, O‐ and S‐based electrophiles as alternatives for the halides are particularly attractive due to the ubiquitous presence of the O‐ and S‐based starting materials in both the natural world and synthetic systems 5.…”