5868
(Entry 4). In the case of naphthalenes, the corresponding tetrahydronaphthalenes were obtained
(Entries 5±8). Reduction of 2-naphthol was more dicult than that of 1-naphthol. Furthermore,
acenaphthene and acenaphthylene were also reduced, respectively (Entries 9 and 10). In the case
of phenol, reduction took place easily at a lower temperature (60ꢀC) to give cyclohexanol in high
yield. Ultrasonication accelerated the reaction (Entries 12 and 13).
The greatest advantage of our method compared with other methods is that the reaction is
operationally simple and safe in aqueous media under mild conditions (90ꢀC and atmospheric
pressure) and hydrogen gas is not necessary because the proton source is water. Furthermore, the
Raney Ni±Al alloy is inexpensive. Recently, in view of environmental concerns, organic reactions
in water without any organic solvents have been receiving attention.22 Therefore, our method is
quite interesting and provides a simple and eective procedure for reduction of aromatic rings.
References
1. For Part 1 and Part 2, see: (a) Tsukinoki, T.; Mitoma, Y.; Nagashima, S.; Kawaji, T.; Hashimoto, I.; Tashiro, M.
Tetrahedron Lett. 1998, 39, 8873±8876. (b) Liu, G.-B.; Tsukinoki, T.; Kanda, T.; Mitoma, Y.; Tashiro, M.
Tetrahedron Lett. 1998, 39, 5991±5994.
2. (a) House, H. O. Modern Synthetic Reactions; Benjamin: Menlo Park, 1972; pp. 1±227. (b) March, J. Advanced
Organic Chemistry; John Wiley & Sons: New York, 1992; pp. 780±783. (c) Olah, G. A.; Molnar, A. Hydrocarbon
Chemistry; John Wiley & Sons: New York, 1995; pp. 446±480.
3. Augustine, R. L. Heterogeneous Catalysis for the Synthetic Chemist; Marcel Dekker: New York, 1996, pp. 403±
437.
4. Minabe, M.; Watanabe, K.; Ayabe, Y.; Yoshida, M.; Toda, T. J. Org. Chem. 1987, 52, 1745±1748.
5. Columbus, I.; Biali, S. E.; Ito, T. J. Am. Chem. Soc. 1999, 3060±3067.
6. Choren, E.; El-Chaar, L.; Hernandez, J. O.; Arteaga, G.; Arteaga, A.; Sanchez, J. J. Mol. Catal. 1992, 72, 85±95.
7. Meister, A.; Meister, G.; Suss-Fink, G. J. Mol. Catal. 1994, 92, 123±126.
8. Okano, T.; Tsukiyama, K.; Konishi, H.; Kiji, J. Chem. Lett. 1982, 603±606.
9. Rothwell, I. P. Chem. Commun. 1997, 1331±1338.
10. Yalpani, M.; Lunow, T.; Koster, R. Chem. Ber. 1989, 122, 687±693.
11. Yalpani, M. Chem. Ber. 1990, 123, 983±987.
12. Marcinow, Z.; Rabideau, P. J. Org. Chem. 1990, 55, 3812±3816.
13. Adams, C. J.; Earle, M. J.; Seddon, K. R. Chem. Commun. 1999, 1043±1044.
14. Raney Ni±Al alloy (Ni: 50%) was purchased from the Kishida Chemical Company.
15. A typical procedure is described as follows: 1% aq. KOH solution (10 ml) was gradually dropped into a mixture of
1 (5 mmol, 650 mg), Raney Ni±Al alloy (3.5 g) and water (10 ml) for 1.5 h at 90ꢀC under atmospheric pressure.
After the reaction mixture was stirred for 4.5 h, the mixture was cooled to room temperature. The insoluble
materials were ®ltered o with Celite and the residue was washed with ethyl acetate. The ®ltrate was extracted with
ethyl acetate and the organic layer was dried over anhydrous magnesium sulfate. The solvent was evaporated in
vacuo to aord 2 (639 mg, 94%) (Run 6).
16. When using a 5% aq. KOH solution under the same conditions as Run 4 in Table 1, the yield of 2 was 40%, but 1
was recovered (55%).
17. Keefer, L. K.; Lunn, G. Chem. Rev. 1989, 89, 459±502.
18. Papa, D.; Schwenk, E.; Whitman, B. J. Org. Chem. 1942, 7, 587±590.
19. When the reduction was undertaken by adding a Raney Ni±Al alloy over 1.5 h to a mixture of 10% aq. NaOH (10
ml) without any organic solvents and 1 (5 mmol) at 90ꢀC, 1 was recovered (95%) (2: 2%). Furthermore, although
the reaction was carried out by adding the Raney Ni±Al alloy at 60ꢀC and then heating up the mixture to 90ꢀC,
the reaction did not proceed (1 was recovered quantitatively).
20. Ungnade, H. E. J. Org. Chem. 1948, 13, 361±370.
21. Wilds, A. L.; Shunk, C. H.; Homan, C. H. J. Am. Chem. Soc. 1954, 76, 1733±1736.
22. (a) Li, C.-J.; Chan, T.-H. Organic Reactions in Aqueous Media; John Wiley & Sons: New York, 1997. (b) Organic
Synthesis in Water; Grieco, P., Ed.; Blackie Academic and Professional: London, 1998.