Synthesis 2005(15): 2619-2622  
DOI: 10.1055/s-2005-872163
SPECIALTOPIC
© Georg Thieme Verlag Stuttgart · New York

Aromatic Carbonyl Compound Reduction and Pinacol Coupling Processes Mediated by Titanocene(III)/Zn in Water

Juan L. Oller-López, Araceli G. Campaña, Juan M. Cuerva*, J. Enrique Oltra*
Department of Organic Chemistry, Faculty of Sciences, University of Granada, Campus Fuentenueva s/n, 18071 Granada, Spain
Fax: +34(958)248437; e-Mail: [email protected]; e-Mail: [email protected];
Further Information

Publication History

Received 7 July 2005
Publication Date:
12 August 2005 (online)

Abstract

A novel procedure for the reduction and pinacol coupling of aromatic aldehydes and ketones mediated by titanocene(III)/Zn in water is described. The titanocene-catalyzed version in sea water proved to be especially convenient for the reduction of aryl ketones. Mechanistically, the reaction presumably proceeds via free-radical chemistry.

    References

  • 1a Engberts JBFN. Blandamer MJ. Chem. Commun.  2001,  1701 
  • 1b Ribe S. Wipf P. Chem. Commun.  2001,  299 
  • 1c Lindström UM. Chem. Rev.  2002,  102:  2751 
  • For excellent overviews on contemporary free-radical chemistry, see:
  • 2a Curran DP. Porter NA. Giese B. Stereochemistry of Radical Reactions   VCH; Weinheim: 1996. 
  • 2b Radicals in Organic Synthesis   Vol. 1,2:  Renaud P. Sibi MP. Wiley-VCH; Weinheim: 2001. 
  • 3 RajanBabu TV. Nugent WA. J. Am. Chem. Soc.  1994,  116:  986 
  • 4 Barrero AF. Oltra JE. Cuerva JM. Rosales A. J. Org. Chem.  2002,  67:  2566 
  • 5 Enemærke RJ. Larsen J. Skrydstrup T. Daasbjerg K. J. Am. Chem. Soc.  2004,  126:  7853 
  • 6a Gansäuer A. Chem. Commun.  1997,  457 
  • 6b Gansäuer A. Bauer D. J. Org. Chem.  1998,  63:  2070 
  • For exhaustive reviews on the chemistry of bis(cyclopentadienyl)titanium(III) chloride in organic solvents, see:
  • 7a Gansäuer A. Bluhm H. Chem. Rev.  2000,  100:  2771 
  • 7b Gansäuer A. Pierobon M. In Radicals in Organic Synthesis   Vol. 2:  Renaud P. Sibi MP. Wiley-VCH; Weinheim: 2001.  p.207-220  
  • 7c Gansäuer A. Rinker B. Tetrahedron  2002,  58:  7017 
  • 7d Gansäuer A. Narayan S. Adv. Synth. Catal.  2002,  344:  465 
  • 7e Gansäuer A. Rinker B. In Titanium and Zirconium in Organic Synthesis   Marek I. Wiley-VCH; Weinheim: 2002.  p.435-450  
  • 7f Gansäuer A. Lauterbach T. Narayan S. Angew. Chem. Int. Ed.  2003,  42:  5556 
  • 8 Barden MC. Schwartz J. J. Am. Chem. Soc.  1996,  118:  5484 
  • 9 Barrero AF. Rosales A. Cuerva JM. Gansäuer A. Oltra JE. Tetrahedron Lett.  2003,  44:  1079 
  • 10 Fürstner A. Csuk R. Rohrer C. Weidmann H. J. Chem. Soc., Perkin Trans. 1  1988,  1729 
  • 12a Sekutowski DG. Stucky GD. Inorg. Chem.  1975,  14:  2192 
  • 12b Sekutowski D. Jungst R. Stucky GD. Inorg. Chem.  1978,  17:  1848 
  • 12c Stephan DW. Organometallics  1992,  11:  996 
  • 13 Tsuzuki S. Honda K. Uchimaru T. Mikami M. Tanabe K. J. Am. Chem. Soc.  2002,  124:  104 
  • 14 Ganguly B. Fuchs B. J. Org. Chem.  2000,  65:  558 
  • 15 Enemærke RJ. Larsen J. Hjøllund GH. Skrydstrup T. Daasbjerg K. Organometallics  2005,  24:  1252 
  • 17 Gansäuer A. Bluhm H. Pierobon M. J. Am. Chem. Soc.  1998,  120:  12849 
  • 18 Tanaka K. Kishigami S. Toda F. J. Org. Chem.  1990,  55:  2981 
  • 19 McDonough W. Braungart M. Anastas PT. Zimmerman JB. Environ. Sci. Technol.  2003,  435A 
11

In the absence of Zn, the red-brown color of a Cp2TiCl2 solution in deoxygenated water became only yellow after ten hours stirring. When we added Zn, however, the color of the solution immediately changed to green and, after a couple of minutes, to blue.

16

Cp2TiCl2 is not too expensive (10 g = 28.50, Aldrich catalogue), but Zn dust is considerably cheaper (1 Kg = 21.70).

20

Mediterranean Sea water was taken from ‘Las Acacias’ beach, Málaga (Spain), in August 2004.