An unusual endo-selective C-H hydroarylationof norbornene by the Rh(I)-catalyzed reactionof benzamides

Abstract

Hydroarylation is an environmentally attractive strategy which incorporates all of the atoms contained in the substrates into the desired products. Almost all the hydroarylations of norbornene reported to date involve an exo-selective reaction. Here we show the endo-selective hydroarylation of norbornene in the Rh(I)-catalyzed reaction of aromatic amides. The addition of sterically bulky carboxylic acids enhances the endo-selectivity of the reaction. The results of deuterium-labeling experiments show that both the ortho-carbon and the ortho-hydrogen atoms of aromatic amides were attached to the same carbon atom of the norbornane skeleton in the hydroarylation product. These results clearly suggest that hydrometalation or carbometalation, which are commonly accepted mechanisms for the catalytic hydroarylation of C–H bonds, are not involved as the key step in the present reaction, and suggest that the reaction involves a rhodium carbene complex generated from norbornene as the key intermediate.

Rhodium‐Catalyzed Alkylation of C−H Bonds in Aromatic Amides with Non‐activated 1‐Alkenes: The Possible Generation of Carbene Intermediates from Alkenes

“…We recently reported on the Rh‐catalyzed reaction of aromatic amides that contain an 8‐aminoquinoline directing group with activated alkenes, such as acrylic esters, styrenes, α,β‐unsaturated lactones, maleimide, norbornene and N ‐vinylphthalimide . In a different system employing a picolinamide auxiliary, we described the alkylation reaction at C8‐position of 1‐naphthylamide using various alkenes .…”

Rhodium‐Catalyzed C(sp2)‐ or C(sp3)−H Bond Functionalization Assisted by Removable Directing Groups

“…Bidentate Amide Directing Groups CÀHb ond activation assisted by ab identate directing group is awell-established procedure for the functionalization of amides because of its strong coordination ability towards am etal center.O ne of the most versatile and reliable bidentate directing groups developed to date is the 8-aminoquinoline amide moiety,w hich was introduced by Daugulis and co-workers in 2005 for use in Pd-catalyzed CÀHarylation reactions. [187][188][189][190][191][192][193] In 2014, the Rh I -catalyzed alkylation of 8-aminoquinoline amides was first reported in the reaction of a,b-unsaturated esters (Scheme 53 a). [173][174][175][176][177][178][179][180][181][182][183][184][185][186] Theu tility of an 8aminoquinoline moiety for the Rh-catalyzed functionalization of amides discussed here was mainly reported by Chatani and co-workers in terms of various alkylation and alkenylation reactions.…”

“…[187] Av ariety of a,bunsaturated esters can be used in this reaction, with the desired products being produced in good to excellent yields. [191] Theresults of deuterium-labeling experiments suggested that commonly accepted mechanisms,such as hydrometalation or carbometalation, do not appear to be applicable for this reaction and that an uncommon rhodium-carbene species is generated from the norbornene. [192] Control experiments suggested that bidentate coordination and the presence of an acidic proton on the amide were required for the success of the reaction.…”

Rhodiumkatalysierte sp2‐ und sp3‐C‐H‐Funktionalisierungen mit entfernbaren dirigierenden Gruppen

“…Der 8‐Aminochinolin‐Baustein kann leicht installiert und wieder entfernt werden, sodass sich viele Arbeitsgruppen auf diese dirigierende Gruppe konzentriert haben . Die hier diskutierte Anwendung des 8‐Aminochinolin‐Bausteins für die Rh‐katalysierte Funktionalisierung von Amiden geht hauptsächlich auf die von Chatani veröffentlichten Alkylierungs‐ und Alkenylierungsreaktionen zurück. Die Rh I ‐katalysierte Alkylierung von 8‐Aminochinolinamiden wurde erstmals 2014 bei der Reaktion von α,β‐ungesättigten Estern diskutiert (Schema a) .…”

“…Kontrollexperimente legten nahe, dass für den Erfolg der Reaktion eine zweizähnige Koordination und die Gegenwart eines acidischen Protons am Amid erforderlich sind. Kürzlich wurde berichtet, dass die Kupplung von Benzamiden mit Norbornen zur ungewöhnlichen Bildung des endo‐ selektiven Kupplungsprodukts 180 führt (Schema d) . Die Ergebnisse der Deuterium‐Markierungsexperimente führten zu der Annahme, dass die gewöhnlicherweise angenommenen Mechanismen, wie Hydrometallierung oder Carbometallierung, bei dieser Reaktion scheinbar nicht auftreten und dass aus dem Norbornen eine ungewöhnliche Rhodium‐Carben‐Spezies gebildet wird.…”