Imines phosphine catalyzed arylation

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

The palladium-phosphine-catalyzed cycloaddition reactions of vinyloxetanes 530 with aryl isocyanates or diaryl-carbodiimides led to 4-vinyl-l,3-oxazin-2-ones 531 or l,3-oxazin-2-imines 532, respectively (Scheme 101). In the absence of phosphine ligands (PPhs, bis(diphenylphosphino)ethane (DPPE), l,3-bis(diphenylphosphino)propane (dppp), no conversion of heterocumulenes was observed. Starting from fused-bicyclic vinyloxetanes, both types of cycloadditions proceeded in a highly stereoselective fashion, affording only the r-isomers of alicycle-condensed 1,3-oxazine derivatives <1999JOC4152>. 

In 2001, Oi et al. [54] reported on the ruthenium(II) phosphine catalyzed re-gioselective arylation of 2-arylpyridines using aryl halides (Eq. 29). C-C bond formation occurs predominantly at the position ortho to the pyridyl group. The same catalyst system is also effective for the arylation of aromatic imines (Eq. 30) [55]. Although the reaction mechanism has not been elucidated, it was proposed that a tetravalent arylruthenium complex,for example,Ru(Ph)(Br)(Cl)2(I) ,reacts electrophilically with the arylimines. Therefore, C-H bond cleavage is believed to proceed via an electrophilic substitution pathway. 

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. 

The peptidic phosphine ligands that had been introduced by Hoveyda and co-workers271 for enantioselective copper-catalyzed Michael additions (see Section 9.12.2.2.1) were also employed successfully in silver-catalyzed asymmetric Mannich reactions.3 Thus, the aryl-substituted imines 372 reacted with various silyl enol ethers in the presence of stoichiometric amounts of isopropanol, as well as catalytic amounts of silver acetate and ligand 373 to... 

The Buchwald series of bulky phosphines containing the tunable bi-aryl moiety have also been shown to allow for the efficient animation of aryl chlorides as well.57 In particular, Pd/L3 catalyzed the reaction between secondary cyclic amines and most aryl chlorides at 80 °C, Secondary acyclic amines and anilines tend to couple best with neutral to electron rich aryl chlorides. Primary aliphatic amines are quite limited to either the amination of o-tolyl chlorides, or more activated primary amines such as benzyl amine. A better ligand for this transformation was reported to be L4 as the amination could be conducted at room temperature in many cases.58 Base sensitive R1 required the use of K3PO4 rather than NaOf-Bu. Most amines work well with this catalyst system, except for unactivated primary aliphatic amines (e.g., n-hexyl amine). Allyl amine, hydrazines, imines, benzyl amine, and (EtO)2CH2NH2 all couple well with aryl chlorides under the... 

Chelating ferrocene phosphine L18 was reported by Hartwig to efficiently catalyze the amination of most aryl chlorides with any type of primary aliphatic amine, imine, or hydrazine at 80-100 °C with NaOf-Bu in DME. Base sensitive aryl chlorides, or those containing acidic protons, may be aminated using LiHMDS as the stoichiometric base. Impressively, catalyst loadings as low as 0.005 mol% can be used. 

On the basis of the same working hypothesis, Sasai et al. have functionalized the 3-position of BINOL with a series of aryl phosphines. Catalyst CP42 was found to catalyze effectively the asymmetric aza-MBH reaction of A-tosyl-imines with vinyl ketones (Scheme 2.132). ... 

The asymmetric addition of phosphorus nucleophiles to imines provides direct access to phosphorus-containing chiral amines. While this chemistry is dominated by the use of phosphites and related compounds, a report by Duan outlines a successful protocol for the asymmetric addition of secondary phosphines to imines (Scheme 4.30) [81]. The reaction was catalyzed by a chiral palladium compound comprised of a palladium(II) center Ugated by a resolved pincer compound. A range of aryl and heteroaryl imines as well as several secondary phosphines were successfully used in this reaction. To aid in the isolation of the phosphines, the authors added elanental sulfur at the end of the P—C bond-fomung reaction. This chenustry provides access to a range of chiral N,P Ugands for metal centers that were previously challenging to prepare and isolate. 

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