Imines rhodium catalyzed arylation

The mechanism of the rhodium catalyzed arylation of imines presumably occurs via an initial transmetallation to produce the arylrhodium species 59 (Figure 1.10). Aryl transfer followed by a second rhodium boron transmetallation (or protonation by water) completes the catalytic cycle. 

Scheme 1.36 Rhodium catalyzed arylation of N arenesulfonyl imines.

Figure 8.4 Examined ligands in the rhodium-catalyzed arylation of imines.

Scheme 6.21 Rhodium-catalyzed arylation of azomethine imines, as described by Hayashi and coworkers [26],...

Rhodium Phosphine-Catalyzed Arylation of Imines The asymmetric rho... 

Rhodium Diene-Catalyzed Arylation of Imines Hayashi has shown that the asymmetric synthesis of diarylmethylamines could be realized with high enantio control by the rhodium catalyzed arylboronic acid addition to N tosyl imines [119]. Ihe rhodium catalyst bears the C2 symmetrical bicyclo 2.2.1]heptadicne ligand 54. 

Rhodium-catalyzed chelation-assisted C—H bond functionalization reactions (enantioselective annulation of aryl imines, dihydropyridine synthesis from imines and ahcynes, one-pot synthesis of pyridines from imines and alkynes, 2-arylpyridine alkylation with imines) 12ACR814. Synthesis of pyridine and dihydropyridine derivatives by regjo- and stereoselective addition to N-activated pyridines 12CRV2642. 

Scheme 8.14 Rhodium-catalyzed enantioselective arylation of imines 42.

Since 2004, considerable progress has been achieved in the rhodium-catalyzed enantioselective addition of arylboronic acids or arylboroxines to various classes of aryl imines 42 (Scheme 8.14). 

Scheme 8.15 Rhodium-catalyzed diastereoselective arylation of imines 57.

Scheme 9.4 Rhodium-catalyzed direct arylation of imine 5 with boronate 6.

During studies on rhodium-catalyzed Suzuki-Miyaura cross-coupling reactions, Miura and coworkers reported more recently on the use of less-toxic tetraphenyl-borate 6 for the direct arylation of imines (Scheme 9.4) [16]. Unfortunately, rather low yields of mono- and di-arylated products were obtained, this being due to a reduction of the starting material via a sequence consisting of a rhodium hydride addition and subsequent protonation. The reduction of the imine is mandatory for the regeneration of a rhodium chloride species, and thereby for catalytic turnover. 

Chelation-assisted ortho arylation of aromatic imines with aryl halides was reported by Oi and Inoue [10b] and Ackermann [14b] (Scheme 17.5). In 2003, Bedford [15a,b] demonstrated the C-H arylation of phenol derivatives at their ortho position using various aryl halides in the presence of a rhodium catalyst. Subsequently, Oi [15c] also reported a similar rhodium-catalyzed C-H arylation of phenols. In 2008, Bedford [15d] reported conditions for the C-H/C-X couphng of simple phenol derivatives. 

Z. Guo, T. Shi, J. Jiang, L. Yang, W. Hu, Org. Biomol. Chem. 2009, 7, 5028-5033. Component match in rhodium catalyzed three-component reactions of ethyl diazoacetate, H O and aryl imines a highly diastereoselective one-step synthesis of 3-aryl isoserine derivatives. 

Since Wakamatsu serendipitously discovered amidocarbonylation while performing the cobalt-catalyzed hydroformyla-tion of olefins in 1971, this unique carbonylation reaction, affording a-amino acids directly from aldehydes, has been extensively studied.More recently, palladium-catalyzed processes have been developed to expand the scope of this reaction.The Pd-catalyzed amidocarbonylation has been applied to aldehydes,aryl halides, and imines. As a related reaction, lactamization " of aryl halides catalyzed by a rhodium complex has also been developed. 

Optically active alcohols, amines, and alkanes can be prepared by the metal catalyzed asymmetric hydrosilylation of ketones, imines, and olefins [77,94,95]. Several catalytic systems have been successfully demonstrated, such as the asymmetric silylation of aryl ketones with rhodium and Pybox ligands however, there are no industrial processes that use asymmetric hydrosilylation. The asymmetric hydrosilyation of olefins to alkylsilanes (and the corresponding alcohol) can be accomplished with palladium catalysts that contain chiral monophosphines with high enantioselectivities (up to 96% ee) and reasonably good turnovers (S/C = 1000) [96]. Unfortunately, high enantioselectivities are only limited to the asymmetric hydrosilylation of styrene derivatives [97]. Hydrosilylation of simple terminal olefins with palladium catalysts that contain the monophosphine, MeO-MOP (67), can be obtained with enantioselectivities in the range of 94-97% ee and regioselectivities of the branched to normal of the products of 66/43 to 94/ 6 (Scheme 26) [98.99]. 

Alkyl and aryl substituted imines have received the most attention as substrates for asymmetric hydrogenation, and the development of the field can therefore be outlined by examining their reductions. These are usually catalyzed by chiral complexes of titanium, ruthenium, rhodium, or iridium, though gold catalysts have also recently proven useful for this purpose [31]. New catalysts are generally tested for the reductions of substrates A-D (Scheme 6.1). 

There have been multiple efforts toward supported catalysts for asymmetric transfer hydrogenation, and the 4 position on the aryl sulfonate group of 26 has proven a convenient site for functionalization. Thus far, this ligand has been supported on dendrimers [181,182], polystyrenes [183], silica gel [184], mesoporous siliceous foam [185], and mesoporous siliceous foam modified with magnetic particles [186]. The resulting modified ligands have been used in combination with ruthenium, rhodium, and iridium to catalyze the asymmetric transfer of imines and, more commonly, ketones. 

Arylation reactions of aromatic ketimines were developed, and in many cases the products of the reaction were isolated after subsequent hydrolysis. Therefore, these arylations constitute an indirect method for the preparation of arylated aromatic ketones, the direct functionalizations of which are often more difficult. Thus, direct arylation of imine 42 with sodium tetraphenylborate catalyzed by [RhCl(cod)]2 afforded a mixture of mono- and diarylated benzophenone imines (44 and 45) (Scheme 9.16) [53]. The formation of the corresponding amine 46 clearly indicated that 42 also acted as a hydride acceptor in this transformation. Most likely, the reaction occurs via initial coordination by the benzophenone imine to a phenylrho-dium intermediate followed by orfho-rhodation to afford the five-membered rhoda-cyde intermediate 47 (Scheme 9.16). Subsequent reductive elimination generates the monophenylated product 44 and a rhodium hydride, which then reduces imine 42 in the presence of ammonium chloride as proton donor to regenerate the catalytically active speties. 

Pioneering studies of the catalytic, enantioselective arylation of imines date back to 2000, when Hayashi disclosed a rhodium/phosphine-catalyzed addition of arylstannanes to N-tosylarylimines (31). Whereas, the method gave rise to highly enantioenriched diarylmethylamines, five equivalents of the stannane were required to obtain high yields. 

Asymmetric Transfer Hydrogenation of Ketones. The first reports on asymmetric transfer hydrogenation (ATH) reactions catalyzed by chiral metallic compounds were published at the end of the seventies. Prochiral ketones were reduced using alcohols as the hydrogen source, and Ru (274,275) or Ir (276) complexes were used as catalysts. Since then, many chiral catalytic systems for homogeneous ATH of ketones, imines, and olefins have been developed (37,38,256,257,277-289). The catalytic systems are usually based on ruthenium, rhodium, or iridium, and the ATH of aryl ketones is by far the most studied. Because of the reversibility of this reaction, at high conversions, a gradual erosion of the ee of the product has been frequently reported. An azeotropic 5 2 mixture of formic acid/triethylamine can be used to overcome this limitation. 

With Rhodium In 2010, the groups of Ellman and Bergman [47] reported the Rh(III)-catalyzed aryla-tion of Boc-Imines (see Chapter 6, for imine arylation) via C-H bond functionalization (Figure 4.22). This in fact was a very interesting method for the synthesis of chiral amines, being complementary to the variety of aryl boronic acid methods that are currently known [48]. 

Scheme 6.3 Proposed mechanism for the catalytic asymmetric arylation of imines catalyzed by a rhodium complex with a phenyltitanium reagent [6],...

A variety of electrophiles are employed for carbonyl alkenylation and arylation that proceed through transmetalation from silicon to transition metal catalysts. For example, addition of alkenylsilanes and aryl(trimethoxy)si lanes to aldehydes is catalyzed by copper/DTBM-SEGPHOS, which mediates transmetalation from silicon to copper to give a wide variety of chiral alcohols with high degree of % ee (Scheme 3-144). The enantioselective alkenylation of imines using 2-(hydroxylmethyl)phenyl-substituted propen-2-ylsilane is catalyzed by a rhodium/chiral diene complex. ... 

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