Dialkylzinc diphenylphosphinoyl imines

Asymmetric addition to ketimine in a reagent controlled manner has seldom been reported, even by 2008. When we investigated the potential for tbis asymmetric addition around 1992, there were no known examples. In 1990, Tomioka et al., reported the first asymmetric addition of alkyl lithium to N-p-methoxyphenyl aldo-imines in the presence ofa chiral (3-amino ether with 40-64% ee [8] (Scheme 1.11). In 1992, Katritzky reported the asymmetric addition of Et2Zn to in situ prepared N-acyl imine in the presence of a chiral (3-amino alcohol with 21-70% ee [15] (Scheme 1.12). In the same year, Soai et al., reported the asymmetric addition of dialkylzinc to diphenylphosphinoyl imines in the presence of chiral (3-amino alcohols with 85-87% ee [16] (Scheme 1.13). These three reports were, to the best of... 

Chiral amines, ArCH(R)NH2, can be prepared by addition of a dialkylzinc to A-(diphenylphosphinoyl)imines, ArCH=N—P(=0)Ph2, using a suitable auxiliary, followed by acid hydrolysis to cleave the phosphorus moiety. A series of 2-azanorbornylmethanols (65) give ee% up to 92%, and they also induce some enantioselectivity in additions to benzaldehyde. A highly organized transition state with two zincs is proposed one coordinates the nitrogens of substrate and catalyst and the other coordinates the oxygens. 

A-diphenylphosphinoyl imines also react with dialkylzinc in the presence of stoichiometric or catalytic amounts of different chiral (see Chiral) ligands (Scheme 24). Acid hydrolysis of the resulting phosphinamides occms without racemization and gives enantiomerically enriched primary amines. The allylation of various cyclic imines was obtained with high enantioselectivity (see Electrophile), 77 to 99% e.e., in the presence of lithiated bis-oxazoline ligands (Scheme 25). 

High enantioselectivity has been achieved on addition of diethylzinc to benzaldehyde catalysed by a chiral diamine, (5)-2-(A/,A/-disubstituted aminomethyl)pyrrolidine," and by chiral helical titanate complexes of tetradentate ligands." Enantioselective additions of dialkylzinc reagents to A/-(diphenylphosphinoyl)imines, promoted by aziridino alcohols," and to the carbon-nitrogen double bond of the nitrone 3,4-dihydroisoquinoline A/-oxide, promoted by dicyclopentyl(i ,i )-tartrate," have also been reported. 

Chiral amines, ArCH(R)NH2, can be prepared by addition of a dialkylzinc to A-(diphenylphosphinoyl)imines, ArCH=N—P(=0)Ph2, using a suitable auxiliary, followed by acid hydrolysis to cleave the phosphorus moiety. A series of... 

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See also in sourсe #XX -- [ ]

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