BINAP ligand imines

Iridium(III) hydride forms complexes with DIOP, BDPP (2,4-bis(diphenyl-phosphino)pentane), NORPHOS, and BINAP ligands to produce amines in 11 -80% ee.679 Similar modest results are obtained in the reduction of N-arylketimines with an iridium(HI) complex with (2S,3 S) -C HIRA PHOS as the chiral ligand.680 The indium complexes with chiral phosphinodihydrooxazoles catalyze the enantioselective hydrogenation of imines in supercritical carbon dioxide with up to 80% ee, but generally lower ee values are observed in... 

Kobayashi and co-workers successfully achieved the asymmetric 1,3-dipolar cycloaddition reaction of azomethine imines with terminal alkynes catalyzed by CuHMDS and DIP-BINAP ligand to provide N,N-bicyclic pyrazolidinone derivatives in high yields with exclusive regioselectivity and excellent enantioselectivity (Scheme 26) [46]. Mechanistic studies elucidated a stepwise reaction pathway and revealed that the steric character of the ligand determines the regioselectivity. Arai and co-workers applied chiral bis(imidazolidine)pyridine-CuOAc complex to the [3+2]cycloaddition of azomethine imines with propiolates for the construction of bicyclic pyrazolo[l,2-a]pyrazolone derivatives with up to 74% ee [47]. 

In asymmetric reactions, chiral phosphine ligands such as BINAP derivatives are used as effective chiral ligands in silver complexes. In particular, an Agr-BINAP complex activates aldehydes and imines effectively and asymmetric allylations,220-222 aldol reactions 223 and Mannich-type reactions224 proceed in high yield with high selectivity (Scheme 51). 

Fig. 1 DIOP, BINAP, and BDPP diphosphine ligands. Summary of the best results obtained in the Ir-catalyzed hydrogenation of several imines...

Asymmetric hydrogenation of imines derived from trifluoropyruvate, in the presence of a chiral complex of palladium (ligand = (R)-BINAP), affords ethyl (/f)-trifluoroalaninate with ca. 90% The ee values strongly depend on the solvent,... 

The N-aryl imines 412 as protected anilines can be prepared by Pd-catalysed arylation of benzophenone imine with aryl halides using DPPF and BINAP as ligands, and aniline derivatives are obtained by deprotection [204a],... 

Presumably, the use of a bidentate ligand such as ( )-BINAP or DPPF results in the occupation of a vacant coordination site, preventing -hydride elimination of the Pd (II) amide intermediate [53]. Dissociation of the imine and C-H bond reductive elimination results in formation of the reduced aryl bromide. If this -hydride elimination is rapid relative to reductive elimination and reversible, then significant erosion of the enantiomeric excess of optically active a-substituted amines maybe observed during the reaction (Scheme 3). 

J0rgensen [105] and Lectka [106] have reported the ene reactions of imines. Both used BINAP as ligands, and a variety of copper salts (Sch. 58). The ee of 266 depended on the counter ion on the copper—PFf, and CIO4 anions gave the highest selectivity. It is also important to note that CuPFs is safer to use than the perchlorate. 

BINAP was first introduced by Noyori [80]. It has been particularly explored for reduction with ruthenium catalysts. BINAP is an atropisomeric ligand because rotation aroimd the central C-C bond is blocked. Accordingly BINAP exists in two enantiomers. Complexes of Ru(II) with BINAP are extremely powerful catalysts for enantioselective hydrogenations of prochiral a,p- and P,Y-unsaturated carboxylic acids, enamides, allylic and homoallylic alcohols, imines etc. [83]. In many cases, the hydrogenation is quantitative with enantiomeric excesses of over 95%. A wide variety of vitamins, terpenes, P-lactam antibiotics, etc. are accessible by the use of catalysts containing the BINAP stereogenic element. An example for 3-oxo carboxylic esters is shown in reaction (1) of Fig. 6.32. 

Another sulfonated derivative of BINAP was mentioned in a patent of Takasago International Corporation [8]. Cationic complexes of ruthenium and or iridium with this ligand - sulfonated on the 5- and 5 -positions of the naphthyl rings - are claimed to affect asymmetric hydrogenation of olefins, ketones, and imines. 

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