H. Matsunaga et al. / Tetrahedron Letters 42 (2001) 8857–8859
8859
Table 3. The hydrogen-transfer reduction of propiophe-
2. For reviews, see: de Graauw, C. F.; Peters, J. A.; van
Bekkum, H.; Huskens, J. Synthesis 1994, 1007–1017 and
references cited therein. Also see: Node, M.; Nishide, K.;
Shigeta, Y.; Shiraki, H.; Obata, K. J. Am. Chem. Soc.
2000, 122, 1927–1936.
a
none with RhCl(PPh3)
3
O
OH
Ph
Ph
3
. For reviews, see: (a) Zassinovic, G.; Mestroni, G. Chem.
Rev. 1992, 92, 1051–1069; (b) Naota, T.; Takaya, H.;
Murahashi, S.-I. Chem. Rev. 1998, 98, 2599–2660 and
references cited therein.
Entry
RhCl(PPh3)3 Temp (°C)
mol%)
Yield (%)b
(
Yb(OTf)3
Without
4
5
6
. Yamakawa, M.; Ito, H.; Noyori, R. J. Am. Chem. Soc.
Yb(OTf)3
2000, 122, 1466–1478 and references cited therein.
. Chowdhury, R. L.; B a¨ ckvall, J.-E. J. Chem. Soc., Chem.
Commun. 1991, 1063–1064.
1
2
3
0.1
35
35
25
89
85
34
67
65
35
0.05
0.05
. The use of Y(OTf) (0.4 mol%) instead of RuCl (PPh )
3
2
3 3
gave only 6% yield of 1-phenyl-1-propanol.
a
Performed with RhCl(PPh3)3 and t-BuOK in the presence of
Yb(OTf)3 in isopropanol for 2 h. For a typical procedure, see Ref.
7. (a) Tsuruta, H.; Yamaguchi, K.; Imamoto, T. J. Chem.
Soc., Chem. Commun. 1999, 1703–1704; (b) Yamanaka,
M.; Nishida, A.; Nakagawa, M. Org. Chem. 2000, 2,
1
2.
b
Isolated yields.
159–161.
8
. Typical procedure for the hydrogen-transfer reaction cat-
alyzed by RuCl (PPh ) : A suspension of RuCl (PPh )
3 3
2
3 3
2
(
19 mg, 0.02 mmol) and Yb(OTf) (0.04 mmol) in isopro-
3
pyl alcohol (IPA) (5 ml) was refluxed for 5 min under an
argon atmosphere followed by dropwise addition of an
isopropanol solution of propiophenone (1.34 g, 10
mmol). After refluxing for 10 min, to this mixture was
added a 1% NaOH solution (0.24 mmol) in IPA, followed
by refluxing for another 2 h. The reaction was quenched
by passing the solution through a silica gel pad and the
usual work-up, followed by chromatographic purification
on a silica gel column (hexane–EtOAc: 19:1–7:3) gave
1-phenyl-1-propanol in 86% yield.
9
. 4-tert-Butylcyclohexanone was readily reduced to give a
mixture of cis- and trans-cyclohexanols in 90–92% yield
with and without Yb(OTf)3.
Scheme 2.
1
1
0. Spogliarich, R.; Zassinovich, G.; Mestroni, G.; Graziani,
M. J. Organomet. Chem. 1980, 198, 81–86.
isopropanol to give Ru(i-PrO) L3 complexes, which
2
would generate the active dihydride species, RuH L ,
2
3
1. The 1:1 and 1:4 ratios of RhCl(PPh ) and Yb(OTf) gave
3
3
3
by b-elimination. Thus, an equimolar mixture of
33 and 12% yields of the corresponding alcohol, respec-
RuCl (PPh ) and Yb(OTf)3 is effective enough to
2
3 3
tively.
accelerate the reaction, though to a moderate extent
Table 1, entry 2). The mechanistic role of Yb(OTf) in
1
2. Typical procedure for the hydrogen-transfer reaction cat-
(
3
alyzed by RhCl(PPh ) : A suspension of RhCl(PPh ) (9
3
3
3 3
accelerating the hydrogen-transfer reaction is not clear
1
4
mg, 0.01 mmol) in isopropyl alcohol (IPA) (5 ml) was
stirred for 5 min under an argon atmosphere at 35°C and
an isopropanol solution of propiophenone (1.34 g, 10
mmol) was added dropwise. After stirring for 10 min at
at present.
In conclusion, the RuCl (PPh ) - and RhCl(PPh ) -cat-
2
3 3
3 3
alyzed hydrogen-transfer reactions reinforced with
3
5°C, Yb(OTf) (0.02 mmol) and a 1% t-BuOK solution
3
Yb(OTf) provide a highly efficient procedure for the
3
(
0.12 mmol) in IPA was added and it was stirred for
reduction of ketones, in which the molar ratio of Ru
another 2 h. The reaction was quenched by passing the
solution through a silica gel pad and the usual work-up,
followed by chromatographic purification on a silica gel
column (hexane–EtOAc: 19:1–7:3) gave 1-phenyl-1-
propanol in 89% yield.
(
Rh) and Yb is critical. This simple and promising
method is of practical use and is readily applicable to
the bulk-scale reduction of ketones.
1
1
3. Aranyos, A.; Csjernyik, G.; Szabo, K. J.; B a¨ ckvall, J.-E.
J. Chem. Soc., Chem. Commun. 1999, 351–352.
References
4. Reduction of propiophenone with RuH (PPh ) and
2
3 4
1
. (a) Meerwein, H.; Schmid, R. Liebigs Ann. Chem. 1925,
RuH (PPh ) –Yb(OTf) (1:2) under identical conditions
gave 63 and 60% yields of the alcohol, respectively, while
the reduction with RhH(PPh3)4 and RhH(PPh3)4–
2 3 4 3
4
8
1
44, 221–238; (b) Verley, A. Bull. Soc. Chim. Fr. 1925, 37,
71–874; (c) Ponndorf, W. Angew. Chem. 1926, 39, 138–
43.
Yb(OTf) (1:2) was unsuccessful.
3