The effects of sulfur substitution in chiral amino thiols on the enantioselective addition of organozinc reagents to aldehydes: a novel method for estimation of free energies of dimerization in monomer–dimer equilibria

Abstract

Differences between the thiol ligand 1 and the corresponding alcohol ligand 2 were observed in the catalytic asymmetric alkylation of benzaldehyde with diethylzinc. The thiol ligand 1 was superior for reaction rate, enantioselectivity and asymmetric amplification. The effects of chiral amino thiols are discussed and compared with the results of chiral amino alcohol counterparts. The quantitative and thermodynamic aspects of the monomer–dimer equilibria involved in thiazazincolidine or oxazazincolidine catalysts have also been studied on the basis of colligative properties.

References

1. (a) For reviews on catalytic addition of organozinc reagents to carbonyl compounds, see R. Noyori and M. Kitamura, Angew. Chem., Int. Ed. Engl., 1991, 30, 49 and K. Soai and S. Niwa, Chem. Rev., 1992, 92, 833; (b) N. Oguni and T. Kanecko, J. Am. Chem. Soc., 1988, 110, 7877; (c) G. B. Hones and S. B. Heaton, Tetrahedron: Asymmetry, 1993, 4, 649; (d) M. Kitamura, S. Suga, K. Kawai and R. Noyori, J. Am. Chem. Soc., 1986, 108, 6071; (e) K. Soai, A. Okawa, T. Kaba and K. Ogawa, J. Am. Chem. Soc., 1987, 109, 7111.
2. (a) J. Kang, J. W. Lee and J. I. Kim, J. Chem. Soc., Chem. Commun., 1994, 2009; (b) J. Kang, D. S. Kim and J. I. Kim, Synlett, 1994, 842.
3. J. Kang, J. W. Kim, J. W. Lee, D. S. Kim and J. I. Kim, submitted.
4. (a) M. Kitamura, S. Okada, S. Suga and R. Noyori, J. Am. Chem. Soc., 1989, 111, 4028; (b) M. Kimtamur, S. Suga, M. Niwa, R. Noyori, Z.-X. Zhai and H. Suga, J. Phys. Chem., 1994, 98, 12776; (c) M. Kitamura, S. Suga, M. Niwa and R. Noyori, J. Am. Chem. Soc., 1995, 117, 4832.
5. K. Soai, S. Yokoyama and T. Hayasaka, J. Org. Chem., 1991, 56, 4264.
6. D. Guillaneus, S. H. Zhao, O. Samuel, D. Rainford and H. B. Kagan, J. Am. Chem. Soc., 1994, 116, 9430 and references cited therein.
7. K. Mikami and M. Terada, Tetrahedron, 1992, 48, 5671.
8. K. Fitzpatrick, R. Hulst and R. M. Kellogg., Tetrahedron: Asymmetry, 1995, 6, 1861.