Diaryl ketimine

Diaryl ketimines, Ar1C=NH. The patent literature has described the preparation of (C6H5)2C=NH by direct reaction of benzophenone with ammonia, but this route has not been investigated further. Actually, a number of diaryl ketimines can be obtained in >95% yield by reaction of a diaryl ketone with liquid ammonia and a catalytic amount of ammonium chloride in THF in a sealed tube at 120° (60 bar). 

Cl-OCR NHCOR. Diaryl ketimines Ar Ar C=NH react with diazodeoxybenzoin in... 

Taking imine activation as an example, the relative roles of proton transfer/ ion-pairing versus hydrogen bonding have been probed for Brpnsted acid catalysis. Taking simple diaryl ketimines and aldimines as model substrates and... 

Several factors other than conjugation and inductive effects have been found to affect the reactivity of the azomethine linkage. Ortho and para hydroxy-substituted diaryl ketimines are unusually stable to-... 

Diaryl ketimines are more stable than alkyl aryl ketimines which in turn are more stable than the purely aliphatic ketimines since conjugation increases the thermodynamic stability of the azomethine linkage Benzophenone imine (3), with a melting point of 48°c is quite stable . Although the monoimine of j>-benzoquinone is very unstable, the diimine (4) is sufficiently stable to be studied spectroscopically . V... 

Analog lieferten Diaryl- und Arylalkyl-ketimine optisch aktive primare Amine. 

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. 

N-Unsubstituierte Ketimine werden am besten mit Platin(IV)-oxid (2071 bar) in was-serfreien Losungsmitteln (Methanol, Athanol) zu prim. Aminen hydriert (Dialkyl-5,6, Alkyl-aryl-7,8, Diaryl-ketimine9). Auch a-Hydroxy- (Essigsaure-athylester, Normalbedingungen)10 und a-tert.-Amino-ketimine (Athanol, 50-5373,5 bar)11 lassen sich mit Platin(IV)-oxid zu den entsprechenden primaren Aminen hydrieren z.B. ... 

Maikov, Kocovsky, and co-workers have developed different L-valine-based Lewis basic catalysts such as 81 [176, 177], for the efficient asymmetric reduction of ketimines 76 with trichlorosilane 2, or catalyst 82 [178] with a fluorous tag, which allows an easy isolation of the product and can be used in the next cycles, while preserving high enantioselectivity in the process. Sigamide catalyst 83 [179, 180] and Lewis base 84 [181] were employed in a low amount (5 mol%) affording final chiral amines 80 with high enantioselectivity (Scheme 30) [182]. Interestingly, 83 was used for the enantioselective preparation of vicinal a-chloroamines and the subsequent synthesis of chiral 1,2-diaryl aziridines. In these developed approaches the same absolute enantiomer was observed in the processes. 

A range of cyclic ketimines (38, X = CH2, O, NR) undergo rhodium-catalysed asymmetric arylation to give gem-diaryl sulfamidates or sulfamides (39) in up to 99% ee. The products can be converted into a-tertiary chiral amine derivatives without loss of enantiomeric purity. 

Following the pioneering discovery by Oi and Inoue on the diarylation of imines [43], improved diarylation of imines was reached in NMP using a Ru(II)/KOAc/ PPhs catalytic system for aldimines and Ru(ll)/2 KOAc without PPhs but for longer time for ketimines. The diarylated imines could be reduced into bulky amines by catalytic hydrosilylation with the same Ru(ll) catalyst. Thus the overall reaction could be performed in two steps via sequential Ru(ll) catalysed C-H bond functionalization/hydrosilylation [(Eq. 19)] [84]. 

More importantly it was found that the ketimines could be more easily diarylated in water in basic medium (K2CO3) than in NMP using the Ru(II)/2KOAc/l PPh3 catalytic system [(Eq. 20a)] [85]. As ketones do not direct ortho C-H bond activation followed by arylation, this arylation of aldimines and ketimes can be used for the access to diarylated aldehydes and ketones that are thus obtained by acidification of their aqueous solution. Oxazoline can also efficiently direct ortho-arylation of aryl groups [(Eq. 20b)] [85]. 

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