Generally, the reaction is completed very quickly within a
few minutes after the addition of TESOTf (or TMSOTf).9,10
Table 2. TESOTf-Catalyzed Reductive Cleavage of Trityl
Ether
We were interested in the chemoselectivity of this novel
reductive cleavage and prepared a variety of 1,10-decanediol
derivatives 8a-g. The acetyl group of 8a was entirely inert
against the reaction conditions, and the reaction of 8a was
completed within 2 min by treatment with 0.02 equiv of
TESOTf and 1.2 equiv of Et3SiH in CH2Cl2 at room
temperature. The crude extract was treated with 80% aqueous
acetic acid in THF at room temperature for 30 min and,
following column chromatography on silica gel, afforded diol
9a in 95% yield (entry 1 of Table 1).7 Using 0.01 or even
Table 1. TESOTf-Catalyzed Reductive Cleavage of Trityl
Ether
a TESOTf was employed as the catalyst. b Employed 3.6 equiv of Et3SiH.
c Employed 2.5 equiv of Et3SiH. d Employed 2.5 equiv of Et3SiH and 0.01
equiv of Et3SiOTf.
TESOTf
(equiv)
yield
(%)b
entry
R
temp
timea
1
2
3
4
5
6
7
8
9
Ac (8a )
Ac (8a )
Ac (8a )
Ac (8a )c
Piv (8b)c
Bz (8c)
0.02
0.01
0.005
0.005
0.02
0.01
0.01
0.01
0.01
0.01
25
25
25
25
25
25
25
25
25
1 min, 10 sec
2 min, 28 sec
13 min, 00 sec
4 min, 30 sec
2 min, 00 sec
3 min, 30 sec
1 min, 20 sec
1 min, 16 sec
4 min, 00 sec
24 min, 00 sec
95
98
91
96
99
95
93
93
89
93d
6). The trityl groups of 8d-f were also cleaved without
causing any damage to the benzyl, MPM, and TBDPS
protecting groups, respectively, under similar reaction condi-
tions. Selective cleavage of trityl ether in the presence of
the MOM group required lower reaction temperatures, and
the yellow color disappeared after 24 min at -48 °C.
Furthermore, TBAF/THF was required for selective cleavage
of the TES group to obtain alcohol 9g in excellent yield
(entry 10). The drying operation7 is critical for preparing
TES ethers 4 in excellent yield since significant quantities
of alcohols were detected by using an ordinary reaction
system.
Bn (8d )
MPM (8e)
TBDPS (8f)
MOM (8g)
10
-48
a Time until the disappearance of the yellow color. b Isolation yield after
acidic treatment using 80% AcOH and THF at room temperature for 30
min. c Reaction was carried out using TMSOTf instead of TESOTf.
d Isolation yield after hydrolysis of TES group by using TBAF in THF at
room temperature for 1 h.
Therefore, we applied our procedure to a variety of sugar
derivatives by using 0.01 equiv of TMSOTf and 1.2 equiv
of Et3SiH. Sugar derivatives generally required a rather
longer reaction period; however, 30 min is sufficient for most
cases. The trityl group of tribenzyl methyl glucoside 10 was
0.005 equiv of TESOTf completed the reaction within 3 or
13 min, respectively (entries 2 and 3). TMSOTf is also useful
for the cleavage of the trityl group and afforded alcohol 9a
in excellent yield (entry 4). The pivaloyl group of 8b and
the benzoyl group of 8c were also inert and afforded alcohols
9b and 9c, respectively, in excellent yields (entries 5 and
(9) General procedure is as follows. To the dried solution of trityl ether
(0.05 M in CH2Cl2) (see ref 8) were added triethylsilane (1.2 equiv) and
trimethylsilyl triflate (0.01 equiv) at room temperature. The resulting yellow
solution was stirred until the color disappeared, and the reaction was
quenched by the addition of water. The crude extract was dissolved in THF
and 80% aqueous acetic acid (1:1), and the solution was stirred for 30 min.
After neutralization, the organic extract was purified by column chroma-
tography on silica gel using hexane/ethyl acetate as an eluant.
(10) Nishizawa, M.; Garc´ıa, D. M.; Yamada, H. Synlett 1992, 797-
799.
(7) (a) Nishizawa, M.; Minagawa, R.; Garc´ıa, D. M.; Hatakeyama, S.
Tetrahedron Lett. 1994, 35, 5891-5894. (b) Nishizawa, M.; Garc´ıa, D.
M.; Minagawa, R.; Noguchi, Y.; Imagawa, H.; Yamada, H.; Watanabe, R.;
Yoo, Y. C.; Azuma, I. Synlett 1996, 452-454. (c) Watanabe, R.; Yoo, Y.
C.; Hata, K.; Mitobe, M.; Koike, Y.; Nishizawa, M.; Garcia, D. M.; Noguchi,
Y.; Imagawa, H.; Yamada, H.; Azuma, I. Vaccine 1999, 17, 1484-1492.
(8) Hatakeyama, S.; Mori, H.; Kitano, K.: Yamada, H.; Nishizawa, M.
Tetrahedron Lett. 1994, 35, 4367-437.
154
Org. Lett., Vol. 5, No. 2, 2003