Catalytic enantioselective Strecker reaction of ketoimines using catalytic amount of TMSCN and stoichiometric amount of HCN

Tetrahedron Letters

Volumn 45, Issue 15, 2004, Pages 3153-3155

  Kato, Nobuki ^a   Suzuki, Masato ^a   Kanai, Motomu ^a   Shibasaki, Masakatsu ^a  

^a UNIVERSITY OF TOKYO   (Japan)

Author keywords

Asymmetric catalysis; Atom economy; Disubstituted amino acids; Ketoimines; Strecker reaction

Indexed keywords

IMINE;

ARTICLE; CATALYSIS; CATALYST; CHEMICAL REACTION; CHIRALITY; ENANTIOSELECTIVITY; REACTION ANALYSIS; REDUCTION; STOICHIOMETRY; STRECKER SYNTHESIS; SYNTHESIS;

EID: 1642348583     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.tetlet.2004.02.077     Document Type: Article

References (16)

1. See the preceding paper Tetrahedron Lett. 2004, 45, 3147-3151.
2. For previous examples for catalytic enantioselective Strecker reaction of ketoimines, see: Vachal P., Jacobsen E.N. Org. Lett. 2:2000;867.
3. Vachal P., Jacobsen E.N. J. Am. Chem. Soc. 124:2002;10012.
4. Chavarot M., Byrne J.J., Chavant P.Y., Vallée Y. Tetrahedron: Asymmetry. 12:2001;1147.
5. Masumoto S., Usuda H., Suzuki M., Kanai M., Shibasaki M. J. Am. Chem. Soc. 125:2003;5634.
6. For an excellent review, see: Gröger H. Chem. Rev. 103:2003;2795.
7. Catalytic asymmetric alkylation is another powerful methodology for disubstituted α-amino acid synthesis. For recent examples, see: Ooi T., Takeuchi M., Kameda M., Maruoka K. J. Am. Chem. Soc. 122:2000;5228.
8. Trost B.M., Dogra K. J. Am. Chem. Soc. 124:2002;7256.
9. Trost B.M. Science. 254:1991;1471.
10. The gadolinium cyanide, not TMSCN itself, is the actual nucleophile in the catalytic cyanosilylation of ketones, confirmed by labeling studies: Yabu K., Masumoto S., Yamasaki S., Hamashima Y., Kanai M., Du W., Curran D.P., Shibasaki M. J. Am. Chem. Soc. 123:2001;9908. See also the proposed catalytic cycle in Ref. 8 (Scheme 2).
11. For the reactivity and enantioselectivity differences between in the absence and presence of protic additive, see Tetrahedron Lett. 2004, 45, 3147-3151.
12. Other factors such as the fact that the substrates are more readily soluble to the reaction media under the TMSCN (cat.)-HCN conditions than under TMSCN-DMP conditions, and/or the retardation effect of the trimethylsilylated DMP, cannot be excluded as origins of the reactivity difference.
13. Lack of reactivity using only HCN is also important from the mechanistic point of view, that is, the pre-catalyst 6 cannot be directly converted to the active catalyst 3 (Scheme 2). Working hypothesis for the catalytic cycle is postulated in Scheme 2, based on these new experimental results and previous mechanistic studies (Ref. 5). The catalytic cycle should always proceed through the intermediary of silylated 2. Thus, TMSCN produced in the active catalyst ( 3 ) formation step functions as a catalyst re-generator (from 6 to 3 through 2 ).
14. High purity of the substrate N-phosphinoylketoimines is very important especially when catalyst loading was reduced. Substrate purification through flash column chromatography followed by recrystallization using anhydrous solvents under argon atmosphere was effective to obtain the substrates with high purity.
15. iPrOH (1:1) in propionitrile (1.1 M) under ice bath for 2 h.
16. Slatta K.H. Ber. 67:1934;1028.