B. Hatano, H. Tagaya / Tetrahedron Letters 44 (2003) 6331–6333
6333
4. Review for supercritical carbon dioxide, see: Leitner, W.
Acc. Chem. Res. 2002, 35, 746.
5. (a) Ikushima, Y.; Hatakeda, K.; Sato, O.; Yokoyama, T.;
Arai, M. Angew. Chem. Int. Ed. 2001, 40, 210; (b) Bro¨ll,
D.; Kaul, C.; Kra¨mer, A.; Krammer, P.; Richter, T.;
Jung, M.; Vogel, H.; Zehner, P. Angew. Chem. Int. Ed.
1999, 38, 2998; (c) Ikushima, Y.; Hatakeda, K.; Sato, O.;
Yokoyama, T.; Arai, M. Angew. Chem. Int. Ed. 1999, 38,
2910; (d) Sato, O.; Ikushima, Y.; Yokoyama, T. J. Org.
Chem. 1998, 63, 9100; (e) Junk, T.; Catallo, W. J. Tetra-
hedron Lett. 1996, 37, 3445; (f) Yao, J.; Evilia, R. F. J.
Am. Chem. Soc. 1994, 116, 11229.
6. (a) High-Temperature Aqueous Solution: Thermodynamic
Properties; Fernandes, P. R. J.; Corti, H. R.; Japer, M.
L., Eds.; CRC: Boca Ration, 1992; (b) Shaw, R. W.;
Brill, T. B.; Clifford, A. A.; Eckert, C. A.; Franck, E. U.
Chem. Eng. News 1991, 69, 26; (c) Haar, L.; Gallagher, J.
S.; Kell, G. S. NBC/NRC Wasserdampftafeln; Springer:
Heidelberg, 1988; pp. 19–214; (d) To¨dheide, K. In
Water—a Comprehensive Treatise Vol. 1; Franks, F., Ed.;
Plenum: New York, 1972; p. 514.
(3)
Table 3. Direct reduction of anthraquinone derivatives
using iPrOHa
1
Additive
Yield (%)b
2k
4k
5k
1k
1k
1l
–
29
–
–
8
–
–
60
90
88
Sulfur
Sulfur
7. Hatano, B.; Kadokawa, J.; Tagaya, H. Tetrahedoron
Lett. 2002, 43, 5859.
8. The reduction of ketones and aldehydes to alcohols using
2-propanol is well known as Meerwein–Ponndorf–Verley
reduction. Reference see: Wilds, A. L. Org. React. 1944,
2, 178.
a Reaction conditions: 1.0 mmol of 1, 5 mL of 2-propanol, at 400°C
under Ar.
b The product was isolated by recrystallization.
9. MPV-reduction using supercritical 2-propanol was
reported. Reference see: (a) Malwitz, V.-D.; Metzger, J.
O. Angew. Chem. 1998, 98, 747; (b) Malwitz, D.; Met-
zger, J. O. Chem. Ber. 1986, 119, 3558
10. To our knowledge, only two attempts have been reported
that 2-propanol in the presence of strong acids or
hydrous tin oxide at 300°C performed as a reductant of
ketones to alkanes. Reference, see: (a) Burton, H.;
Cheeseman, G. W. H. J. Chem. Soc. 1953, 986; (c)
Takahashi, K.; Shibagaki, M.; Kuno, H.; Matsushita, H.
Bull. Chem. Soc. Jpn. 1994, 67, 1107.
Scheme 2.
11. A typical procedure is as follows: in a tubular steel bomb
reactor (10 mL) were placed 1 (2.0 mmol) and 2-propanol
(5 mL) under argon atmosphere, and the reactor was
sealed with the steel cap, and kept at 350°C for 5 h in a
sand bath. After the reactor was cooled to room temper-
ature in a water bath, the resulting mixture was extracted
with ethyl acetate (10 mL) and concentrated. The residue
was purified by bulb-to-bulb distillation. The yields were
shown in Table 2.
12. Aromatization using sulfur is well known. Reference, see:
(a) Newman, M. S.; Din, Z. U. J. Org. Chem. 1971, 36,
966; (b) Crawford, M.; Supanekar, V. R. J. Org. Chem.
1964, 2380; (c) Blair, H. S.; Crawford, M.; Spence, J. M.;
Supanekar, V. R. J. Org. Chem. 1960, 3313.
synthetic utility of supercritical 2-propanol as well as
the simplicity and cleanliness of procedures. More
detailed studies on other synthetic applications in
supercritical fluids are now underway.
References
1. (a) Anastas, P. T.; Warner, J. Green Chemistry Theory
and Practice; Oxford University Press: Oxford, 1998; p.
160; (b) Anastas, P. T.; Warner, J. Green Chemistry:
Frontiers in Benign Chemical Syntheses and Processes;
Oxford University Press: Oxford, 1998; p. 364.
2. Recently reviews, see: Oakes, R. S.; Clifford, A. A.;
Rayner, C. M. J. Chem. Soc., Perkin Trans. 1 2001, 917.
3. Reviews for sub- and supercritical water, see: (a) Akiya,
N.; Savage, P. E. Chem. Rev. 2002, 102, 2725; (b)
Katritzky, A. R.; Nichols, D. A.; Siskin, M.; Murugan,
R.; Balasubramanian, M. Chem. Rev. 2001, 101, 837.
13. Acetone, which was probably formed in disproportiona-
tion of 6, was detected by GC-MS.
14. Using 2-propanol-d8 instead of 2-propanol-d0 under
supercritical conditions (350°C, 134 kg/cm2), the
diphenylmethane-d2 was obtained in 90% yield.