Asymmetric Michael additions with nitrogen-based

The asymmetric addition of glycine enolates to acrylates was also achieved by use of the tartaric acid-derived phase-transfer catalysts 27 and 28 (Scheme 4.9). Arai, Nishida and Tsuji [13] showed that the C2-symmetric ammonium cations 27a,b afford up to 77% ee when t-butyl acrylate is used as acceptor. The cations 28 are the most effective/selective PTC identified by broad variation of the substituents present on both the acetal moiety and nitrogen atoms [14], In this study by Shibasaki et al. enantiomeric excesses up to 82% were achieved by use of the catalyst 28a (Scheme 4.9) [14], Scheme 4.9 also shows the structure of the guanidine 29 prepared by Ma and Cheng in the absence of additional base this also catalyzes the Michael addition of the glycine derivative 22 to ethyl acrylate, albeit with modest ee of 30% [15],... 

Based on the finding that ruthenium complexes catalyzed the Michael addition of cyanoesters, Ito developed a system of RhH(CO)(PPh3)3 and chiral bi-dentated phosphine, (S,S)-(P,P)-TRAP. The catalyst promoted the asymmetric addition of 66 to 7 giving R)-67 [64, 65, 66]. In the case of a reactive acceptor, acrolein, even 0.1 mol % of the complex effectively catalyzed the reaction. An enantiomeric excess of up to 93% was attained with the diisopropylmethyl ester. Since BINAP, DIOP, CHIRAPHOS, etc., did not induce such high stereoselectivities, the frans-coordinated structure constructed by the TRAP was considered to be critical. The structure of the ruthenium complex obtained by X-ray analysis indicated the interaction of the metal with the nitrile nitrogen atom. The frans-coordinated ligand might be required to affect the remote reaction site. 

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