Phosphinoylimines chiral, additions

Enantioselective Addition of Dialkylzincs to Imines. Enantioselective addition of dialkylzincs to N-diphenyl-phosphinoylimines in the presence of DBNE or its analog affords optically active phosphoramides. Subsequent hydrolysis affords optically active amines in up to 91% ee (eq 25). When the amount of DBNE is catalytic (10 mol %), the enantioselec-tivity is 75% ee. One of the advantages of this method over the alkyllithium method is the use of a lesser amount of chiral ligand. 

The tremendous success in the catalytic asymmetric addition of organozinc reagents to aldehydes spurred Itsuno and co-workers to examine the reactivity of diethylzinc with silyl imines in the presence of chiral amino alcohols and diols. Unfortunately, this type of azomethine function failed to react [23a]. The use of activated N-acyl- and iV-phosphinoylimines turned out to be crucial as evidenced by the following reports on the alkylation of these functions using di-... 

In 1992, Soai reported the synthesis of enantiomerically enriched amines by the reaction of organozinc reagents with M-diphenylphosphinoylimines [35a, 35b, 35c]. The diphenylphosphinoyl moiety provided the necessary activation of the C=N bond to observe dialkylzinc additions. The reactivity of a series of three N-diphenylphosphinoylimines 22a-c was examined in the presence of Et2Zn and a substoichiometric or a stoichiometric amount of the chiral 3-amino alcohols 18 or 21 (<0.1 g of phosphinoylimine, ca. 0.17 M) (Scheme 13). 

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