NNN-Ruthenium Catalysts for the Synthesis of Pyridines, Quinolines, and Pyrroles by Acceptorless Dehydrogenative Condensation

Abstract

The bidentate ruthenium complex (HO-C 5 H 3 N-CO-C 5 H 3 N-C 5 H 4 N)Ru(CO) 2 Cl 2 (2) could transform to a tridentate product (HO-C 5 H 3 N-CO-C 5 H 3 N-C 5 H 4 N)Ru(CO)Cl 2 (3), which further reacted with CH 3 ONa in the presence of PPh 3 to convert to two complexes 5), via −OH deprotonation. The catalytic coupling cyclizations of secondary alcohols with amino alcohols were investigated, and complex 3 exhibited the highest activity. The coupling reactions proceeded in air with only 0.2 mol % catalyst loading and had a broad scope for the synthesis of pyridines, quinolones, and pyrroles. ■ RESULTS AND DISCUSSIONSynthesis and Characterization of the Ligand and Complexes. As shown in Scheme 1, ligand 1 was obtained by the reaction of HBr (40% in water) with (6-methoxypyridin-2yl)(6-(pyridin-2-yl)pyridin-2-yl)methanone at reflux for 3 h in

Phosphine Ligand‐Free Ruthenium Complexes as Efficient Catalysts for the Synthesis of Quinolines and Pyridines by Acceptorless Dehydrogenative Coupling Reactions

“…In the presence of KOtBu, the condensation of aminobenzaldehyde Taken previous reports [40][41][42][43][44]82,88] into account, we propose a possible mechanism for Ru catalyzed ADC reaction as depicted in…”

“…Catalyst 1 b showed better activity with higher TOFs than nonfunctionalized catalysts including RuCl(CO)(PPh 3 ) 2 (saz) (H 2 saz=salicylaldazine) and Ru( η 6 ‐ p ‐cymene)Cl(pad) (pad=pyrrole‐2‐aldehydehydrazones) . It was also superior to the functionalized phosphine‐containing complexes like RuClH(CO)(dpbp) (dpbp=6‐((di‐ tert ‐butylphosphanyl)methyl)‐2,2′‐bipyridine), Mn(CO) 3 (btpea)Br (btpea=2‐( tert ‐butylthio)‐ N ‐(pyridin‐2‐ylmethyl)ethan‐1‐amine), MnBr(CO) 2 (pehp) (pehp=( E )‐2‐(2‐(1‐(pyridin‐2‐yl)ethylidene)hydrazinyl)pyridine), but inferior to the more sophisticated complexes such as RuClH(CO)(dpmppa) (dpmppa= N ‐(di‐ tert ‐butylphosphanyl)‐6‐(1‐methyl‐1 H ‐pyrazol‐3‐yl)pyridin‐2‐amine), RuCl(PPh 3 ) 2 (phpy) (phpy=6‐(1,10‐phenanthrolin‐2‐yl)pyridin‐2‐ol) and RuCl 2 (CO)(bphm) (bphm=[2,2′‐bipyridin]‐6‐yl(6‐hydroxypyridin‐2‐yl)methanone) . The catalytic activity of 1 b for the synthesis of 2,6‐diphenylpyridine was slightly lower than the phosphine‐supported complexes such as RuH(CO)(PPh 3 )(dppeqa) (dppeqa= N ‐(2‐(diphenylphosphanyl)ethyl)‐5,6,7,8‐tetrahydroquinolin‐8‐amine), RuClH(CO)(dpbp), RuClH(CO)(dpmppa), and RuCl 2 (CO)(bphm) (Table S4 in the Supporting Information).…”

“…[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][60][61][62][63] Metal-ligand cooperative catalysis [64][65][66][67] can dramatically improve catalytic performance of ADC reactions using pincer ligands bearing NH, OH or CH 2 functionality. [40][41][42][43][44][68][69][70][71][72][73][74][75][76][77][78][79][80][81] Milstein, [40] Sun, [41] Yu, [42] Kundu [43] and Chen [44] have independently developed bifunctional Ru(II) catalysts for the synthesis of pyridine and quinoline derivatives (Scheme 1), but these catalysts were often air/water sensitive, involved a somewhat complicated synthesis, or required to...…”

Cycloamination strategies for renewable N-heterocycles

“…For instance, coupling cyclization of amino alcohols and alcohols with desired functionalities with suitable spatial distances is able to selectively afford pyrrole, pyridine, quinoline, pyrazine, carbazole, or acridine derivatives. [318][319][320][321][322] Chiral N-heterocyclic compounds have a privileged role in pharmaceuticals. 323 A specific chiral source of asymmetric induction (i.e., chiral catalyst) is typically required for the enantioselective synthesis of N-heterocycles, 324,325 through which stereoselective upgrading of thermodynamically stable CO 2 to optically pure azaheterocycles can be realized.…”

Bidentate Ru(II)‐NC Complexes as Catalysts for α‐Alkylation of Unactivated Amides and Esters

“…Recently, our group has reported several transition metal complexes for borrowing hydrogen reactions, [16] including αalkylation of ketones. [16c-d] As an extension, herein we present a bidentate Ru(II)-NC complex {(C 5 H 4 N)-(C 6 H 4 )}RuCl(CO)(PPh 3 ) 2 (1), which is active for the dehydrogenative reaction from primary alcohols to carboxylic acids, [17] for α-alkylation of unactivated amides and esters with alcohols (Scheme 1).…”