Stereoselective preparation of quaternary benzylic centres using chiral imidazolines†

Abstract

Dianions derived from C₂ symmetric chiral imidazolines provide good to excellent stereocontrol in alkylation reactions affording fully substituted benzylic centres.

References

1. Recent reviews on stereoselective alkylation using organometallic intermediates alkyl halides: (a) P. Beak, A. Basu, D. J. Gallagher, Y. S. Park and S. Thayumanavan, Acc. Chem. Res., 1996, 29, 552; (b) D. Seebach, A. R. Sting and M. Hoffmann, Angew. Chem., Int. Ed. Engl., 1996, 35, 2708; (c) Stereoselective Synthesis, in Houben-Weyl-Methods of Organic Chemistry, ed. G. Helmchen, R. W. Hoffmann, J. Mulzer and E. Schaumann, Thieme, Stuttgart, 1995, vol. E21a, pp. 762–881; (d) D. Hoppe, F. Hinze, P. Tebben, M. Paetow, H. Ahrens, J. Schwerdtfeger, P. Sommerfeld, J. Haller, W. Guarnieri, S. Kolczewski, T. Hense and I. Hoppe, Pure Appl. Chem., 1994, 66, 1479.
2. E. Lorthiois, I. Marek and J.-F. Normant, Bull. Soc. Chim. Fr., 1997, 134, 333; L. Micoulin, V. Jullian, J. C. Quirion and H. P. Husson, Tetrahedron: Asymmetry, 1996, 7, 2839; T. L. Elworthy and A. I. Meyers, Tetrahedron, 1994, 50, 6089; A. I. Meyers, Tetrahedron, 1992, 48, 2589; D. Romo and A. I. Meyers, Tetrahedron, 1991, 47, 9503; H.-J. Gais, G. Hellmann, H. Günther, F. Lopez, H. J. Lindner and S. Braun, Angew. Chem., Int. Ed. Engl., 1989, 28, 1025.
3. A. I. Meyers and G. P. Brengel, Chem. Commun., 1997, 1; A. I. Meyers, M. A. Seefeld, B. A. Lefker and J. F. Blake, J. Am. Chem. Soc., 1997, 119, 4564; I. Hoppe, M. Marsch, K. Harms, G. Boche and D. Hoppe, Angew. Chem., Int. Ed. Engl., 1995, 34, 2158.
4. (a) C. Kouklovsky, A. Pouilhès and Y. Langlois, J. Am. Chem. Soc., 1990, 112, 6672; (b) T. Berranger and Y. Langlois, J. Org. Chem., 1995, 60, 1720; (c) P. I. Dalko and Y. Langlois, Tetrahedron Lett., 1992, 33, 5213.
5. A. G. Myers, J. L. Gleason, T. Yoon and D. W. Kung, J. Am. Chem. Soc., 1997, 119, 656 and references cited therein.
6. For use of ¹³C NMR spectroscopy in investigating the structure of metalation products see G. Fraenkel and F. Qiu, J. Am. Chem. Soc., 1997, 119, 3571; H. J. Reich and J. E. Holladay, J. Am. Chem. Soc., 1995, 117, 8470; G. Fraenkel and K. V. Martin, J. Am. Chem. Soc., 1995, 117, 10 336; D. Croisat, J. Seyden-Penne, T. Strzalko and L. Wartski, J. Org. Chem., 1992, 57, 6435.
7. ¹J_C-H couplings are diagnostic, and were used routinely to provide structural information. In particular, these couplings have been shown to be directly proportional to the fraction of s-character in the given C-H bonds, and this has been used to investigate the hybridization of molecules. See J. R. Abraham, J. FisherP. LoftusIntroduction to NMR Spectroscopy, Wiley, Chichester, 1988, pp. 51–53; E. Breitmaier and W. Voelter, Carbon-13 NMR Spectroscopy, 3rd edn. VCH, New York, 1987, pp. 134–140.
8. S. Thayumanavan, A. Basu and P. Beak, J. Am. Chem. Soc., 1997, 119, 8209.
9. For a review concerning the creation of asymmetric quaternary centres see K. Fuji, Chem. Rev., 1993, 93, 2037.