F. Zaccheria et al. / Tetrahedron Letters 46 (2005) 7743–7745
7745
tron donor substituents, give also some condensation
compounds (entry 5). The specific reduction of 9,10-
anthraquinone to 9,10-dihydro-anthracene is worth
highlighting as this reaction usually gives mixture of
products.11,12
Experimental conditions: A solution of the substrate
(100 mg) in toluene (8 mL) was transferred under N2
in the reaction vessel containing the catalyst previously
reduced (100 mg). Catalytic tests were carried out at
90 °C at atmospheric pressure of hydrogen under
magnetic stirring. Reaction mixtures were analyzed
by GC (5% phenyl–95% methylpolysiloxane capillary
Entry 1b shows that the catalyst/substrate ratio can
be conveniently reduced to 1/5 without loss in
productivity expressed as mmolprod/gcat h. However, a
further decrease in the ratio results in much slower
reactions.
1
column, 30 m), GC–MS and by H NMR.
References and notes
1. Baumann, K.; Knapp, H.; Strnadt, G.; Schulz, G.;
Grassberger, M. A. Tetrahedron Lett. 1999, 40, 7761–
7764.
2. Ketcha, D. M.; Lieurance, B. A.; Homan, D. F. J. J. Org.
Chem. 1989, 54, 4350–4356.
3. Lee, W. Y.; Park, C. H.; Kim, H. J.; Kim, S. J. Org. Chem.
1994, 59, 878–884.
4. Studer, M.; Burkhardt, S.; Indolese, A. F.; Blaser, H.-U.
Chem. Commun. 2000, 1327–1328.
5. Lau, C. K.; Tardif, S.; Dufresne, C.; Scheigetz, J. J. Org.
Chem. 1989, 54, 491–494, and references cited therein.
6. Wei, T.; Lan, Y.; Xu, J. Heteroatom Chem. 2005, 16, 2–5,
and references cited therein.
7. Nystrom, R. F.; Berger, C. R. A. J. Am. Chem. Soc. 1958,
80, 2896–2898.
This work shows that the use of Cu/Al2O3 or Cu/SiO2
represents a powerful catalytic switch in the reduction
of aromatic ketones. Thus, preparation of the material
using Al2O3 as the support and pre-reduction at
180 °C result in a very mild catalyst showing excellent
selectivity towards formation of the corresponding
alcohols without the need of any basic additive.13
On the other hand, by only changing the support
and rising the activation temperature to 270 °C it is
possible to obtain a catalyst that selectively converts
aromatic carbonyl groups into methylene ones under
very mild conditions and without the use of any acidic
additive.
8. West, C. T.; Donnelly, S. J.; Kooistra, D. A.; Doyle, M. P.
J. Org. Chem. 1973, 38, 2675–2681, and references cited
therein.
9. Chandrasekhar, S.; Raji Reddy, Ch.; Nagendra Babu, B.
J. Org. Chem. 2002, 67, 9080–9082, and references cited
therein.
10. Nishiyama, Y.; Hamanaka, S.; Ogawa, A.; Kambe, N.;
Sonoda, N. J. Org. Chem. 1988, 53, 1326–1329.
11. Kogan, V.; Aizenshtat, Z.; Neumann, R. Angew. Chem.,
Int. Ed. 1999, 38, 3331–3334.
12. Hatano, B.; Tagaya, H. Tetrahedron Lett. 2003, 44, 6331–
6333.
13. Zaccheria, F.; Ravasio, N.; Psaro, R.; Fusi, A. Tetrahe-
dron Lett. 2005, 46, 3695–3697.
14. Ravasio, N.; Zaccheria, F.; Guidotti, M.; Psaro, R. Top.
Catal. 2004, 27, 157–168.
15. Zaccheria, F.; Psaro, R.; Ravasio, N.; De Gioia, L.
Catalysis of organic reactions. In Chemical Industries
Series; Ford, M. E., Ed.; Marcel Dekker: New York, 2001;
pp 601–608.
16. Ravasio, N.; Antenori, M.; Babudri, F.; Gargano, M.
Tetrahedron Lett. 1997, 38, 7103–7106.
Both catalysts can be prepared in a simple way and
are not pyrophoric nor pyrogenic even in their
reduced form. Their heterogeneous nature and very high
selectivity avoid formation of inorganic and organic
wastes.
Catalyst preparation: 20 g of SiO2 (Grace Davison,
BET = 320 m2/g, PV = 1.79 mL/g) was added to a
[Cu(NH3)4]2+ solution prepared by adding NH4OH to
a Cu(NO3)2Æ3H2O solution (8 g in 50 ml) until pH = 9.
After 20 min under stirring, the slurry held in ice bath
was slowly diluted to allow hydrolysis of the copper
complex and deposition of the finely dispersed product
to occur. The solid was separated by filtration, washed
with water, dried overnight at 120 °C and calcined in
air at 350 °C for 4 h. Before reaction, the catalyst ob-
tained (Cu = 8% by weight) was reduced at 270 °C with
H2 (1 atm) before use, removing water formed under re-
duced pressure.