Rhodium imine arylation

Synthesis of diarylmethylamine derivatives, Ar1 -CH( Ar2 )-NHS02-C(dl4-p-N02, has been achieved enantioselectively using rhodium-catalysed arylation of imines with arylboroxines.56... 

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.

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]. 

For these rhodium-cattilyzed arylations, once again Hayashi s group [26] studied other azomethine imines as substrates for this reaction type. The application of sodium tetraarylborate as nucleophile and a chirtil diene ligand similar to the one used previously (see Scheme 6.20) resulted in the preparation of a family of chirtil l-(diarylmethyl)-pyrtizolidin-3-ones in excellent yields and enantioselec-tivities (Scheme 6.21). 

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

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. 

A three-component reaction of aryl diazoacetates, alcohols, and araldehydes (or araldimines) has been investigated, using a rhodium(II) catalyst.283 The first two components combine in the presence of catalyst to produce a zwitterion (72a). Evidence for equilibration with an alcoholic oxonium ylide intermediate (72b) is presented. It is proposed that this species is trapped by electron-deficient araldehyde (or imine) to give new C-C bond formation. 

The addition of arylboronic acids to imines in an aqueous solvent gave a mixture of amine (Eq. 6) and alcohol (Eq. 4) because the imines were partially hydrolyzed to the aldehyde during the reaction. The use of Ph4BNa in place of phenylboronic acid allowed the catalytic addition to various N-sulfonyl imines in the absence of water (Eq. 6). The representative results are summarized in Table 5. The cationic rhodium complexes such as [Rh(cod)(MeCN)2]BF4 was found to be the most efficient catalyst for both aromatic and aliphatic N-sulfonyl imines whereas no reactions were observed for N-alkyl and N-aryl imine derivatives. 

Other organometallic compounds, including aUylic stannanes, allylic samarium, allylic germanium, and allylic indium compounds add to aldi-mines in the same manner. Aryltrialkylstannanes also add the aryl group to Al-tosyl imines using a rhodium catalyst and sonication. Catalytic enantioselective addition reactions are well known, including reactions in an ionic liquid.Allylic... 

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]. 

Scheme 1.21). This catalyst provides the addition product derived from the N tosyl imines of aryl substituted aldehydes in high yield and enantiocontrol. It is believed that the addition proceeds via the formation of a methylrhodium species obtained by the reaction between the rhodium catalyst and dimethylzinc. 

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. 

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). 

A brief comparison of the advantages and disadvantages of titanium, ruthenium, rhodium, iridium, and gold catalysts for the asymmetric hydrogenation of alkyl and aryl substituted imines is given in Table 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. 

The mechanism of this transformation was not investigated, however a possible mechanism was proposed (Scheme 32). Transmetalation of the organoboron reagent to a rhodium(I) center could be followed by coordination of the imine, oxidative addition of the ortho C-H bond and reductive elimination to afford the ortho arylated product and a rhodium(I) hydride. Reoxidation would then follow through insertion of the imine in to the Rh-H bond followed by protonation with NH4C1. 

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. 

Coordination-assisted aromatic arylation reactions using ruthenium [122-125] and rhodium [125, 126] catalysts have been reported. In the reactions, substrates having a neutral heteroatom such as pyridines and aromatic imines are usually employed and are reacted with aryl halides or arylmetal reagents. The palladium(II)-promoted arylation reaction of pyridines and imines having a tert-hutyl group with arylsilanes is also known (Eq. 51) [127]. The reaction proceeds via initial transmetalation to form a PhPd(II) species, which is coordinated by the substrate, and then one of the aliphatic C-H bonds is activated. 

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. 

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