Silylarenhydrierung – ein strategischer Ansatz für einen direkten Zugang zu silylierten gesättigten Carbo‐ und Heterocyclen

Abstract

Ein Verfahren zur Umwandlung leichtzugänglicher silylierter Arene in silylierte gesättigte Carbo-und Heterocyclen mittels Arenhydrierung wurde entwickelt. Die Substratbreite umfasst Alkoxy-und Halogensilylgruppen. Silylgruppen kçnnen in eine Vielzahl von funktionellen Gruppen umgewandelt werden und finden Anwendung in der Synthese, der Materialwissenschaft sowie der pharmazeutischen, agrochemischen und Duftstoff-Forschung. Silylierte gesättigte (Hetero)cyclen sind mit anderen Methoden nur schwer zugänglich. Die Ausbeute der Hydrierung hängt von der Menge des Kieselgel-Additivs ab.D ieser SiO 2 -Effekt ermçglicht ebenfalls eine signifikante Verbesserung des zuvor berichteten Verfahrens fürdie Hydrierung hochfluorierter Arene (z. B. zu all-cis-C 6 H 6 F 6 ).

Enantio‐ and Diastereoselective, Complete Hydrogenation of Benzofurans by Cascade Catalysis

“…Although the high chemoselectivity of catalyst 4 could be leveraged to preserve the sensitive fluoro moiety, defluorination levels were still comparatively high. The beneficial effect of silica gel as supporting material in these terms, which we observed in earlier studies, [13] could not be exploited in the dual catalytic system, since it deactivated catalyst 3 and yielded a racemic product mixture (similarly for acidic alumina, Table 1, entries 7 and 8). In the course of our optimization we observed that an elevated reaction temperature of 60 8C was necessary to activate the rhodium catalyst in the presence of 3, lower temperatures were not sufficient to achieve full conversion (Table 1, entry 10).…”

Access to Unexplored 3D Chemical Space: cis‐Selective Arene Hydrogenation for the Synthesis of Saturated Cyclic Boronic Acids

“…Employing 5 a (0.1 mmol), H 2 (50 bar), 40 °C, and dichloromethane as a solvent, a series of previously established organometallic arene‐hydrogenation pre‐catalysts such as [Rh‐CAAC(COD)Cl] (CAAC=cyclic (alkyl)(amino)carbene, COD=1,5‐cyclooctadiene) ( 1 ), [24] [Rh(COD)Cl] 2 ( 2 ), [( η 5 ‐C 5 Me 5 )Rh(ppy)H] ( 3 ), and [Ru( p ‐cymene)Cl 2 ] 2 ( 4 ) were chosen for hydrogenation. Our group, [21a, 22, 23, 25] Zeng, [20, 26] Bullock, [27] and others [28] have established several arene hydrogenation catalytic systems utilizing complex 1 and its analogs as pre‐catalysts. Lately, it is well‐established that complex 1 , in the presence of molecular sieves or silica and hydrogen, generates the supported Rh 0 ‐nanoparticles in situ which further catalyze the arene‐hydrogenation reaction [23, 25a] .…”

“…Under reductive conditions, such sensitive substituents can influence the reactivity and drive towards the reaction termination or defunctionalization. Encouraged by the recent reports on arene hydrogenation by the group of Zheng on chemo‐selective hydrogenation of aromatic ketones, [20] along with our group on cis ‐selective hydrogenation of fluoroarenes, [21] silylated [22] and borylated [23] arenes, we set to perform the hydrogenation of benzoxaborole, benzoxaborinin, and benzoxaboripin derivatives. The major challenge for the hydrogenation of these derivatives is to overcome the undesirable hydro‐defunctionalization, ring‐opening, or metal‐catalyzed homocoupling products.…”

Selective Arene Hydrogenation for Direct Access to Saturated Carbo‐ and Heterocycles

“…[71] Making use of the facile accessibility of silylated arenes (75), ageneral, cis-selective procedure to access such products was provided by an arene hydrogenation catalyzed by rhodium-CAAC 33 (Figure 18 A). [72] Notably,t he synthetically most useful alkoxy-and halosilyl substituents were welltolerated, thus generating the products (76 a,b)t hat can be used as building blocks in polymer chemistry or organic synthesis. [73] During optimization, as ignificant enhancement of the yield was observed when using increased amounts of the silica gel additive.T his positive effect was also applied to the previously low-yielding hydrogenation of very highly fluorinated arenes and facilitated almost quantitative yields (6;F igure 16).…”