Highly Chemoselective Crossed Imino Pinacol Coupling Reaction Using the Synergetic Effect of Boron Trifluoride Etherate and Trichloromethylsilane

Abstract

Use of boron trifluoride etherate and trichloromethyl­silane in the presence of zinc-copper couple effects a crossed imino pinacol coupling reaction to give 1,2-diamines in good yields with high diastereoselectivities.

Key words

crossed imino pinacol coupling - boron trifluoride etherate - trichloromethylsilane - 1,2-diamines - zinc-copper couple

References

• 1 Lucet D. Gall TL. Mioskowski C. Angew. Chem. Int. Ed.  1998,  37:  2580 
• 2a Reetz MT. Jaeger R. Drewlies R. Hübel M. Angew. Chem., Int. Ed. Engl.  1991,  30:  103 
• 2b Enders D. Schiffers R. Synthesis  1996,  53 
• 2c Tanner D. Birgersson C. Dhaliwal HK. Tetrahedron Lett.  1990,  31:  1903 
• 2d Meguro M. Asao N. Yamamoto Y. Tetrahedron Lett.  1994,  35:  7395 
• 2e Chong A. Oshima K. Sharpless KB. J. Am. Chem. Soc.  1977,  99:  3420 
• 2f Shimizu M. Kamei M. Fujisawa T. Tetrahedron Lett.  1995,  36:  8607 
• 3a Shono T. Kise N. Oike H. Yoshimoto M. Okazaki E. Tetrahedron Lett.  1992,  33:  5559 
• 3b Shimizu M. Iida T. Fujisawa T. Chem. Lett.  1995,  609 
• 3c Taniguchi N. Uemura M. Synlett  1997,  51 
• 3d Kise N. Kashiwagi K. Watanabe M. Yoshida J. J. Org. Chem.  1996,  61:  428 
• 3e Viso A. Fernández de la Pradilla R. Guerrero-Strachan C. Alonso M. Martínez-Ripoll M. André I. J. Org. Chem.  1997,  62:  2316 
• 3f Alvarez-Ibarra C. Csák AG. Colmenero B. Quiroga ML. J. Org. Chem.  1997,  62:  2478 
• 3g Adams H. Anderson JC. Peace S. Pennell AMK. J. Org. Chem.  1998,  63:  9932 
• 4a Corey EJ. Pyne SG. Tetrahedron Lett.  1983,  24:  2821 
• 4b Roskamp EJ. Pedersen SF. J. Am. Chem. Soc.  1987,  109:  6551 
• 4c Shono T. Kise N. Kunimi N. Nomura R. Chem. Lett.  1991,  2191 
• 4d Hanamoto T. Inanaga J. Tetrahedron Lett.  1991,  32:  3555 
• 4e Ito H. Taguchi T. Hanzawa Y. Tetrahedron Lett.  1992,  33:  4469 
• 4f Takai K. Ishiyama T. Yasue H. Nobunaka T. Itoh M. Oshiki T. Mashima K. Tani K. Organometallics  1998,  17:  5128 
• 4g Machrouchi F. Namy J.-L. Tetrahedron Lett.  1999,  40:  1315 
• 4h Ma Y. Zhang Y. Zhou L. J. Chem. Res.  2000,  250 
• 4i Taniguchi N. Uemura M. J. Am. Chem. Soc.  2000,  122:  8301 
• 4j Liu Y.-K. Zhang Y.-M. Liu X. Chin. J. Chem.  2001,  19:  500 
• 5 Shimizu M. Iwata A. Makino H. Synlett  2002,  1538 
• 8 Shimizu M. Makino H. Tetrahedron Lett.  2001,  42:  8865 

6

A typical experimental procedure is as follows: To a suspension of Zn-Cu (32.7 mg, 0.50 mmol) in MeCN (0.25 mL) was added a mixture of BF₃·OEt₂ (78.1 mg, 0.55 mmol) and MeSiCl₃ (0.147 mL, 1.25 mmol) in MeCN (1.0 mL) at 0 °C under an argon atmosphere. To the resulting mixture was added a solution of N-benzylidene-p-anisidine (52.8 mg, 0.25 mmol) and N-benzylidene-p-chlorophenyl aniline (53.9 mg, 0.25 mmol) in acetonitrile (1.25 mL) at 0 °C. After being stirred at room temperature for 1 h, the reaction was quenched with sat. aqueous NaHCO₃. Usual work-up followed by purification on preparative silica gel TLC⁹ deactivated with phosphate buffer gave 1-(4-chloro-phenylamino)-2-(4-methoxyphenylamino)-1,2-diphenyl-ethane (76.2 mg, 71%) as a yellow amorphous.

7

The relative stereochemistry of the product was determined using ¹H NMR (NOE) after transforming into the corresponding imidazolidinone as in the following examples (Scheme [6] ).

Scheme 6

9

The buffered silica gel TLC was used for the purification. The buffered silica gel was prepared by suspending 93 g of silica gel (Merck 60F₂₅₄) in 230 mL of phosphate buffer solution (pH 7.0) for 2 h and dried.