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.
Key words
green-chemistry - radical reactions - titanium - water - zinc
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
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
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
11 In the absence of Zn, the red-brown color of a Cp2 TiCl2 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.
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
16 Cp2 TiCl2 is not too expensive (10 g = 28.50, Aldrich catalogue), but Zn dust is considerably cheaper (1 Kg = 21.70).
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
20 Mediterranean Sea water was taken from ‘Las Acacias’ beach, Málaga (Spain), in August 2004.
