Radical deoxygenation of alcohols via their trifluoroacetate derivatives with diphenylsilane

Article abstract of DOI:10.1016/S0040-4039(00)02184-5

Trifluoroacetate derivatives of alcohols can be used as precursors for the radical deoxygenation of alcohols with diphenylsilane. The reaction afforded high isolated yields of the deoxygenated products and neutral reaction conditions.

Full text of DOI:10.1016/S0040-4039(00)02184-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 1073–1075
Radical deoxygenation of alcohols via their trifluoroacetate
derivatives with diphenylsilane
a,
b
a
a
Doo Ok Jang, * Joonggon Kim, Dae Hyan Cho and Chan-Moon Chung
a
Department of Chemistry, Yonsei University, Wonju 220-710, South Korea
b
Hanwha Group Research & Engineering Center, Taejon 305-345, South Korea
Received 10 October 2000; revised 21 November 2000; accepted 24 November 2000
Abstract—Trifluoroacetate derivatives of alcohols can be used as precursors for the radical deoxygenation of alcohols with
diphenylsilane. The reaction afforded high isolated yields of the deoxygenated products and neutral reaction conditions. © 2001
Elsevier Science Ltd. All rights reserved.
Reactions for the selective deoxygenation of alcohols
are very important processes in organic synthesis, espe-
cially for the synthesis of biologically important
molecules. Among various methods reported for the
deoxygenation of alcohols, the radical deoxygenation of
alcohols (Barton–McCombie reaction) is the most fre-
strong bases and the derivatizing reagents for the
thionocarbonates such as phenyl chlorothionocarbon-
ate, p-fluorophenyl chlorothionocarbonate and diimi-
dazolyl thioketone are relatively expensive and unstable
in moisture. Although carbonyl derivatives of alcohols
can be prepared more readily, they are rarely used in
1
quently used. The Barton–McCombie reaction offers
10
the radical deoxygenation of alcohols. We wish to
suitable reaction conditions that sensitive polyfunction-
alized compounds can tolerate. The Barton–McCombie
reaction has been a protocol for the selective deoxy-
Table 1. Radical deoxygenation of carbonyl derivatives of
a
2
cyclododecanol with diphenylsilane
genation of alcohols since it was reported.
O
X
H
Although organotin hydrides are used commonly as
radical hydrogen sources in the radical deoxygenation
of alcohols, they have several drawbacks including tox-
icity and difficulty of removing the tin by-product from
the desired products. There have been several research
efforts to find alternatives to organotin hydrides such as
t
Ph SiH , ( BuO)
2
2
2
O
o
1
40 C, 20 h
3
4
5
Entry
X
Yield (GC, %)
silanes, hypophosphorous acid, dialkyl phosphites,
6
7
dialkylphosphine oxides and phosphine-boranes.
1
2
3
4
5
6
7
Ph
68
75
65
69
3
CH
3
The radical deoxygenation of alcohols was accom-
plished via the reduction of their various thionocar-
t
Bu
Imidazolyl
OCH3
bonyl
dithiocarbonate,
fluorophenyl
thionocarbonate derivatives of alcohols are widely
used due to their reactivity. However, the procedure for
the preparation of S-methyl dithionocarbonate requires
derivatives.
Among
phenyl thionocarbonate,
thionocarbonate
them,
S-methyl
2
8
p-
OCH CH
5
2
3
6
and
imidazolyl
CF
CF3
3
90
98
93
2
,9
b,c
8
9
b,d
CF3
a
A typical procedure was as follows unless noted otherwise: A
mixture of carbonyl derivative of cyclodecanol (1 equiv.), diphenyl-
silane (4 equiv.) and di-tert-butyl peroxide (1 equiv.) was heated at
140°C. After 20 h the mixture was analyzed by GC.
5 Equiv. of diphenylsilane was used.
Keywords: radical reactions; alcohols; deoxygenation; esters; reduc-
tions.
b
c
*
Corresponding author. Fax: 82 33 760 2182; e-mail: dojang@
The reaction time was 15 h.
d
dragon.yonsei.ac.kr
At 130°C.
0
040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)02184-5

1
074
D. O. Jang et al. / Tetrahedron Letters 42 (2001) 1073–1075
a
Table 2. Radical deoxygenation of various alcohols via their trifluoroacetate derivatives with diphenysilane
Isolated
Yield (%)
Entry
Substrate
Product
O
1
2
85
83
C10H21
O
CF3
C10H21
Ph
H
Ph
O
Ph
O
CF3
CF3
Ph
H
O
H
8
7
1
3
C H
C H
6 13
6
13
3
4
O
O
CF3
H
Ph
Ph
O
O
CF3
O
H
5
6
65
87
C H
8
17
C H
8
17
O
F3C
O
H
O
O
O
O
CF3
O
O
O
O
7
8
83
82
H
O
O
O
O
O
O
O
H
CF3
O
O
O
O
O
O
O
O
O
aA mixture of trifluoroacetate of alcohol (0.4 mmol, 1 equiv.), diphenylsilane
(2.0 mmol, 5 equiv.) and di-tert-butyl peroxide (0.4 mmol, 1 equiv.) was sealed
o
in an ampule under argon. After heating at 140 C for 15 h, the deoxygenated
product was isolated by column chromatography on silica gel.
report herein that the deoxygenation of alcohols can be
accomplished efficiently via their trifluoroacetate
derivatives with diphenylsilane.
The yields of cyclodecane were measured by GLC
analysis and the results are summarized in Table 1.
Ester derivatives of cyclododecanol afforded cyclodode-
cane in moderate yields (entries 1–4), while the carbon-
ate derivatives of alcohols gave a trace amount of
cyclododecane along with the recovered starting mate-
rial (entries 5 and 6). Among the carbonyl derivatives
Initially, the reaction of various carbonyl derivatives of
cyclododecane with diphenylsilane in the presence of
di-tert-butyl peroxide as the initiator was examined.

D. O. Jang et al. / Tetrahedron Letters 42 (2001) 1073–1075
1075
we investigated, the trifluoroacetate of alcohol showed
the most promising results. When the reaction of trifl-
uoroacetate of cyclododecanol with diphenylsilane was
carried out at 140°C in the presence of di-tert-butyl
peroxide as the initiator in a sealed tube, cyclododecane
was obtained in 90% yield with a small amount of the
recovered starting material (entry 7). Finally, the reac-
tion could be optimized to give 98% yield of cyclodode-
cane (entry 8). Although a longer reaction time was
required, the reaction was proceeded at 130°C (entry 9).
M. Tetrahedron 1987, 43, 3541; (d) Hartig, W. Tetra-
hedron 1983, 39, 2609.
2. Barton, D. H. R.; McCombie, S. W. J. Chem. Soc.,
Perkin Trans. 1 1975, 1574.
3. (a) Oba, M.; Nishiyama, K. Synthesis 1994, 624; (b)
Nishiyama, K.; Oba, M.; Oshimi, M.; Sugawara, T.;
Ueno, R. Tetrahedron Lett. 1993, 23, 3745; (c) Barton, D.
H. R.; Jang, D. O.; Jaszberenyi, J. Cs. Tetrahedron 1993,
49, 7193; (d) Barton, D. H. R.; Jang, D. O.; Jaszberenyi,
J. Cs. Tetrahedron 1993, 49, 2793; (e) Barton, D. H. R.;
Jang, D. O.; Jaszberenyi, J. Cs. Tetrahedron Lett. 1992,
33, 6629; (f) Chatgilialoglu, C. Acc. Chem. Res. 1992, 25,
188; (g) Barton, D. H. R.; Jang, D. O.; Jaszberenyi, J. Cs.
Synlett 1991, 435; (h) Barton, D. H. R.; Jang, D. O.;
Jaszberenyi, J. Cs. Tetrahedron Lett. 1991, 32, 7187; (i)
Cole, S. J.; Kirwan, J. N.; Roberts, B. P.; Wills, C. R. J.
Chem. Soc., Perkin Trans. 1 1991, 103; (j) Kirwan, J. N.;
Roberts, B. P.; Willis, C. R. Tetrahedron Lett. 1990, 31,
5093; (k) Barton, D. H. R.; Jang, D. O.; Jaszberenyi, J.
Cs. Tetrahedron Lett. 1990, 31, 4681.
The reaction was applied to the deoxygenation of vari-
ous alcohols. The results are summarized in Table 2.
Secondary alcohols and even the primary alcohols were
efficiently transformed into the corresponding hydro-
carbons (entries 1–4). Tertiary alcohols afforded some-
what lower yields of the deoxygenated products (entry
5
). The process could be used for the deoxygenation of
steroids. Dihydrocholesteryl trifluoroacetate was con-
verted into the corresponding hydrocarbon in 87% yield
(
entry 6). Selective deoxygenation of sugars is a very
4. (a) Jang, D. O. Tetrahedron Lett. 1996, 37, 5367; (b)
Barton, D. H. R.; Jang, D. O.; Jaszberenyi, J. Cs. J. Org.
Chem. 1993, 58, 6838; (c) Barton, D. H. R.; Jang, D. O.;
Jaszberenyi, J. Cs. Tetrahedron Lett. 1992, 33, 5709.
5. Barton, D. H. R.; Jang, D. O.; Jaszberenyi, J. Cs. Tetra-
hedron Lett. 1992, 33, 2311.
6. (a) Jang, D. O.; Cho, D. Y.; Barton, D. H. R. Synlett
1998, 39; (b) Jang, D. O.; Cho, D. Y.; Kim, J. Synth.
Commun. 1998, 28, 3559.
7. Barton, D. H. R.; Jacob, M. Tetrahedron Lett. 1998, 39,
1331.
8. Robins, M. J.; Wilson, J. S.; Hansske, F. J. Am. Chem.
Soc. 1983, 105, 4059.
important tool for the modification of sugars that are
widely used as antibiotics and chiral building blocks in
organic synthesis. The trifluoroacetates could be uti-
lized for the preparation of deoxysugars. Trifluoroac-
etates of secondary alcohol of 1,2:5,6-di-O-isopropyli-
dene-a-
di-O-isopropylidene-a-
deoxygenated product in 83 and 82% yield, respectively,
under the conditions (entries 7 and 8). In summary,
trifluoroacetate derivatives of alcohols can be used as
precursors for the radical deoxygenation of various
alcohols. They can be prepared without using toxic,
expensive derivatizing reagents.
1
1
D
-glucofuranose and primary alcohol of 1,2:3,4-
-galactopyranose produced the
D
9. Carney, R. E.; McAlpine, J. B.; Jackson, M.; Stanaszek,
R. S.; Washburn, M.; Cirovic, M.; Mueller, S. L. J.
Antibiot. 1978, 31, 441.
Acknowledgements
10. (a) Sano, H.; Taketa, T.; Migita, T. Synthesis 1988, 402;
(
b) Saito, I.; Ikehira, H.; Kasatani, R.; Watanabe, M.;
Matsuura, T. J. Am. Chem. Soc. 1986, 108, 3115; (c)
Boar, R. B.; Joukhadar, L.; McGhie, J. F.; Misra, S. C.;
Barrett, A. G. M.; Barton, D. H. R.; Prokopiou, P. A. J.
Chem. Soc., Chem. Commun. 1978, 68; (d) Dashayes, H.;
Pete, J. P.; Portella, C. Tetrahedron Lett. 1976, 2019; (e)
Baldwin, S. W.; Haut, S. A. J. Org. Chem. 1975, 40, 3885;
This work was supported by Korea Research Founda-
tion Grant (1999-015-DP0219).
References
(
f) Khoo, L. E.; Lee, H. H. Tetrahedron Lett. 1968, 4351.
1
. (a) Motherwell, W. B.; Crich, D. Free Radical Chain
Reactions in Organic Synthesis; Academic Press: London,
11. Williams, N. R.; Wander, J. D. In The Carbohydrates;
Pigman, W.; Horton, D., Eds.; Academic Press: London,
1980; Vol. IB, p. 761.
1
992; (b) Curran, D. P. Synthesis 1988, 417; (c) Ramaiah,
.