First Enantio-Flexible Fluorination Reaction Using Metal-Bis(oxazoline) Complexes

Abstract

The first examples of an elective sense of enantioselectivity in enantioselective fluorination reaction using (S,S)-bis(oxazoline)-Ph complexed with Cu(II) or Ni(II) are described.

Key words

fluorine - halogenation - nickel - copper - asymmetric catalysis

References

• 1 Asymmetric Fluoroorganic Chemistry: Synthesis, Application, and Future Directions   Ramachandran PV. ACS Symposium Series 746, American Chemical Society; Washington DC: 2000. 
• 2a Differding E. Lang RW. Tetrahedron Lett.  1988,  29:  6087 
• 2b Davis FA. Han W. Tetrahedron Lett.  1991,  32:  1631 
• 2c Davis FA. Zhou P. Murphy CK. Sundarababu G. Qi H. Han W. Przeslawski RM. Chen B.-C. Carroll PJ. J. Org. Chem.  1998,  63:  2273 
• 2d Takeuchi Y. Suzuki T. Satoh A. Shiragami T. Shibata N. J. Org. Chem.  1999,  64:  5708 
• 2e Shibata N. Liu Z. Takeuchi Y. Chem. Pharm. Bull.  2000,  48:  1954 
• 2f Liu Z. Shibata N. Takeuchi Y. J. Org. Chem.  2000,  65:  7583 
• 3a Muniz K. Angew. Chem. Int. Ed.  2001,  40:  1653 
• 3b Hintermann L. Togni A. Angew. Chem. Int. Ed.  2000,  39:  4359 
• 3c Piana S. Devillers I. Togni A. Rothlisberger U. Angew. Chem. Int. Ed.  2002,  41:  979 
• 3d Togni A. Mezzetti A. Barthazy P. Becker C. Devillers I. Frantz R. Hintermann L. Perseghini M. Sanna M. Chimia  2000,  55:  801 
• 3e Cahard D. Audouard C. Plaquevent J.-C. Roques N. Org. Lett.  2000,  2:  3699 
• 3f Mohar B. Baudoux J. Plaquevent J.-C. Cahard D. Angew. Chem. Int. Ed.  2001,  40:  4214 
• 3g Kim DY. Park EJ. Org. Lett.  2002,  4:  545 
• 3h Hamashima Y. Yagi K. Takano H. Tamas L. Sodeoka M. J. Am. Chem. Soc.  2002,  124:  14530 
• 4a Shibata N. Suzuki E. Takeuchi Y. J. Am. Chem. Soc.  2000,  122:  10728 
• 4b Shibata N. Suzuki E. Asahi T. Shiro M. J. Am. Chem. Soc.  2001,  123:  7001 
• 4c Shibata N. Ishimaru T. Suzuki E. Kirk KL. J. Org. Chem.  2003,  68:  2494 
• 4d Shibata N. Pharmacia  2003,  39:  666 
• 5 Bruns S. Haufe G. J. Fluorine Chem.  2000,  104:  247 
• 6a Kim YH. Acc. Chem. Res.  2001,  34:  955 
• 6b Sibi MP. Liu M. Curr. Org. Chem.  2001,  5:  719 
• 7 Comprehensive Asymmetric Catalysis   Jacobsen EN. Pfaltz A. Yamamoto H. Springer-Verlag; Berlin: 1999. 
• For reviews of C ₂-bis(oxazoline) metal complexes as catalysts, see for example:
• 8a Ghosh AK. Mathivanen P. Cappiello J. Tetrahedron: Asymmetry  1998,  9:  1 
• 8b Jørgensen KA. Johannsen M. Yao S. Audrain H. Thorhauge J. Acc. Chem. Res.  1999,  32:  605 
• 8c Evans DA. Rovis T. Johnson JS. Pure Appl. Chem.  1999,  71:  1407 
• 8d Jørgensen KA. Angew. Chem. Int. Ed.  2000,  39:  3558 
• 8e Johnson JS. Evans DA. Acc. Chem. Res.  2000,  33:  325 
• 9a Nakamura S. Nakagawa R. Watanabe Y. Toru T. Angew. Chem. Int. Ed.  2000,  39:  353 
• 9b Nakamura S. Nakagawa R. Watanabe Y. Toru T. J. Am. Chem. Soc.  2000,  122:  11340 
• Just before the submission of this manuscript, Cu(II)-bis(oxazoline)-catalyzed halogenations have been reported:
• 10a Enantioselective fluorination reaction using Cu(II)-bis(oxazoline): Ma J.-A. Cahard D. Tetrahedron: Asymmetry  2004,  15:  1007 
• 10b Enantioselective bromination and chlorination reactions using Cu(II)-bis(oxazoline): Marigo M. Kumaragurubaran N. Jørgensen KA. Chem.-Eur. J.  2004,  10:  2133 
• 11a Evans DA. Downey CW. Hubbs JL. J. Am. Chem. Soc.  2003,  125:  8706 
• 11b Itoh K. Kanemasa S. J. Am. Chem. Soc.  2002,  124:  13394 
• 11c Kanemasa S. Oderaotoshi Y. Tanaka J. Wada E. J. Am. Chem. Soc.  1998,  120:  12355 
• 12a Evans DA. Johnson JS. Burgey CS. Campos CR. Tetrahedron Lett.  1999,  40:  2879 
• 12b Evans DA. Johnson JS. Olhava EJ. J. Am. Chem. Soc.  2000,  122:  1635 
• 12c Thorhauge J. Roberson M. Hazell RG. Jørgensen KA. Chem.-Eur. J.  2002,  8:  1888 
• 15 After this work was submitted the Ru(II)-catalyzed asymmetric fluorination of β-ketoesters with NFSI using N,N′-bis{o-[bis(phenyl)phosphino]benzylidene}-(1S,2S)-diaminocyclohexane was briefly reported in the review. See: Ibrahim H. Togni A. Chem. Commun.  2004,  1147 

13

Although we tentatively speculate the geometry of the metal centers as shown in Figure [2] , they can be changed depending on the conditions, counter anions and substrates. Geometry optimizations are under being performed by MO calculations and X-ray crystallographic studies of the intermediates.

14

General Procedure: Metal salt (10 mol%) and the (S,S)-bis(oxazoline)-Ph (10 mol%) were stirred under vacuum for 2 h at r.t. Dry solvent (1 mL, and 4 Å molecular sieves) was added under nitrogen atmosphere and stirred for 1 h. Then a solution of substrate 1 (0.10-0.20 mmol) in dry solvent (2 mL) was added to the catalyst solution. After stirring for another 30 min, the reaction vessel was dipped into a temperature-controlled bath as indicated in Table [1] , N-fluorobenzenesulfonimide (1.2 equiv) was added directly to the mixture. The reaction was stirred at the temperature for 1 h to overnight with monitoring by TLC; it was stopped by the addition of H₂O (note; when NFSI was added at -10 °C, the resulting mixture was allowed to warm to r.t. overnight). The reaction mixture was then diluted with CH₂Cl₂, washed with sat. aq Na₂CO₃ solution and brine, dried over MgSO₄ and the solvent was evaporated under reduced pressure. The residue was purified by column chromatography on silica gel eluting with hexane-EtOAc to give the fluorinated product. The ee of the product was determined by chiral HPLC on CHIRALPAK AD-H column.