Water as a Hydroxy Source in a Rh^III‐Catalyzed Directed C−H Hydroxylation of 2‐Arylpyridines

Abstract

A[ Rh III Cp*]-catalyzed directed CÀHh ydroxylation of 2-arylpyridines is described (Cp* = 1,2,3,4,, in which the combinationo f [(RhCp*Cl 2 ) 2 ]/AgF,P hI(OPiv) 2 ,a nd water is used an effective catalytic system. According to our mechanistic studies,i n-cluding 18 O-labeling experiments and X-ray crystallographic analysis of an intermediate Rh complex,w ed emonstrate that water and PhI(OPiv) 2 are required for Rh catalysis as the hydroxy source and the oxidant, respectively. Results and DiscussionWe began our study by using 2-phenylpyridine (1)a samodel substrate in the presence of aR h III catalysta nd hypervalent iodine as an oxidant( Ta ble 1). When [(RhCp*Cl 2 ) 2 ]( 3mol %), PhI(OPiv) 2 (2.0 equiv), AgF (12 mol %), and water (10 equiv) were added to 2-phenylpyridine (1)i nM eCN (0.1 m), 2-(pyridin-2-yl)phenol( 2)w as obtained with high conversion (> 99 %) after heating at 120 8Cf or 15 h( Table 1, entry 1). However,t he reactiond id not proceed at all in the absence of [(RhCp*Cl 2 ) 2 ] or when Pd(OAc) 2 or [{RuCl 2 (p-cymene)} 2 ]w as used instead of [(RhCp*Cl 2 ) 2 ], thus indicating the criticalrole of the Rh III catalyst Scheme1.DirectedCsp 2 ÀHb ond hydroxylation of 2-arylpyridine.

Organometallic Ru(ii), Rh(iii) and Re(i) complexes of sterane-based bidentate ligands: synthesis, solution speciation, interaction with biomolecules and anticancer activity

“…In general, ligands that exhibit the ( N , O ) binding mode, such as 8-hydroxyquinolines or 2-picolinates, tend to form highly stable half-sandwich Ru or Rh complexes; 39–41 however, the 2-(pyridin-2-yl)phenolate-type ligands form a six-membered chelate ring, which is not favored. The crystal structures of Pd( ii ), Cu( ii ) and half-sandwich Rh( iii ) complexes with similar ligands showed rotation around the C–C bond connecting the two aromatic rings, resulting in a significant deviation from a planar structure; 42–45 this most probably contributes to the decreased stability compared to the complexes formed with bpy-type ligands.…”

Synthesis of 2-(Pyridin-2-yl)phenols and 2-(Pyridin-2-yl)anilines

“…Yellow solid (1.42 g, 61% yield); R f = 0.70 and 0.24 (EtOAc/hexane = 1:2); mp 79.0−79.3 °C; IR (neat): 2945,2865,1710,1590,1488,1431,1383,1264,1216,1111,1022,888,781, 730 cm −1 ; 1 H NMR (400 MHz, CDCl 3 ): δ = 15.7 (brs, 1H), 8.92 (dd, J = 2.4, 0.8 Hz, 1H), 8.22 (dd, J = 8.8, 2.4 Hz, 1H), 7.12 (dd, J = 8.8, 0.8 Hz, 1H), 3.93 (s, 3H), 2.43−2.35 (m, 4H), 1.81−1.73 (m, 4H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ): δ = 167. 7,165.6,162.8,146.6,137.7,120.2,116.1,101.0,52.2,30.6,24.6,23.0,cyclohexan-1-one (2q). Orange solid (1.02 g, 31% yield); R f = 0.70 (EtOAc/hexane = 1:2); mp 126.8−127.8 °C; IR (neat): 3029,2883,2827,2536,2165,1632,1593,1533,1480,1449,1356,1199,1097,909,871,761,699, 625 cm −1 ; 1 H NMR (400 MHz, CDCl 3 ): δ = 15.7 (brs, 1H), 8.62−8.61 (m, 1H), 8.39 (d,J = 5.6 Hz,1H),4H),17H),3H), 4.12 (dd, J = 10.8, 6.0 Hz, 1H), 3.37−3.26 (m, 1H), 3.02−2.93 (m, 1H), 2.76 (dd, J = 14.4, 5.6 Hz, 1H), 2.73− 2.60 (m, 3H), 2.58−2.42 (m, 4H), 2.41−2.12 (m, 2H), 2.11−1.97 (m, 2H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ): δ = 208.9, 163.…”

Microwave‐Assisted and Base‐Promoted Domino Reaction of Cyclic N‐Sulfonyl Ketimines with α,β‐Disubstituted Nitroalkenes: A Green Access to 2‐Hydroxyarylpyridines

“…On the other hand, the synthesis of functionalized 2‐pyridylphenol derivatives is rapidly growing interest in recent times due to their valuable applications in light‐emitting materials and bioactive molecules . In this context, the direct C−H hydroxylation of 2‐arylpyridines catalyzed by several expensive transition‐metal‐salts (e. g. Pd(II),– Rh(III),– Ru(II) etc) has been greatly followed for preparing those compounds. However, this process requires high temperature, a large amount of oxidants (K 2 S 2 O 8 , TBHP, H 2 O 2 , oxone, NHPI, PIDA etc) and longer reaction time.…”