D. J. Harrison et al. / Tetrahedron Letters 45 (2004) 8493–8496
8495
[HBcat]
tallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK. Supplementary data associated with
this article can be found, in the online version, at
R2SO
[Rh(III)]
Bcat
[Rh(I)]
H
[Rh(III)]
Bcat
R2S
O
H
R2S + HOBcat
[Rh(III)]
H
[Rh(III)]
H
R2S
R2S
References and notes
O
O
Bcat
1. (a) Madesclaire, M. Tetrahedron 1988, 44, 6537; (b)
Nicolas, E.; Vilaseca, M.; Giralt, E. Tetrahedron 1995,
51, 5701; (c) Kukushkin, V. Y. Coord. Chem. Rev. 1995,
139, 375; (d) Fujiki, K.; Kurita, S.; Yoshida, E. Synth.
Commun. 1996, 19, 3619; (e) Wang, Y.; Koreeda, M.
Synlett 1996, 885; (f) Shimizu, M.; Shibuya, K.; Hay-
akawa, R. Synlett 2000, 1437; (g) Abo, M.; Dejima, M.;
Asano, F.; Okubo, A.; Yamazaki, S. Tetrahedron: Asym-
metry 2000, 11, 823; (h) Nicolau, K. C.; Kuombis, A. E.;
Synder, S. A.; Simonsen, K. B. Angew. Chem., Int. Ed.
2000, 39, 2529; (i) Karimi, B.; Zareyee, D. Synthesis 2003,
335; (j) Boyd, D. R.; Sharma, N. D.; Haughey, S. A.;
Kennedy, M. A.; Malone, J. F.; Shepherd, S. D.; Allen, C.
C. R.; Dalton, H. Tetrahedron 2004, 60, 549.
catB
Figure 2. Rhodium-catalyzed deoxygenation of sulfoxides using
HBcat.
dppe = 1,2-bis(diphenylphosphino)ethane) can be used
to facilitate this addition using only 2equiv of HBcat.17
Reactions proceed cleanly at room temperature to give
the desired product and are usually complete within
1h. Unfortunately, reactions with phenyl vinyl sulfoxide
are also complicated by a competing catalyzed hydro-
boration of the vinyl group.
2. Black, S.; Harte, E. M.; Hudson, B.; Wartofsky, L. J. Biol.
Chem. 1960, 235, 2910.
3. Iranpoor, N.; Firauzabadi, H.; Reza Shaterian, H. J. Org.
Chem. 2002, 67, 2826.
4. Miller, S. J.; Collier, T. R.; Wu, W. Tetrahedron Lett.
2000, 41, 3781.
5. Cha, J. S.; Kim, J. E.; Kim, J. D. Tetrahedron Lett. 1985,
26, 6453.
6. Guidon, Y.; Atkinson, J. G.; Morton, H. E. J. Org. Chem.
1984, 49, 4538.
7. Pelter, A.; Smith, K.; Brown, H. C. Borane Reagents;
Academic: New York, 1988.
8. Sulfoxides were available commercially or prepared by an
established procedure. Langler, R. F.; Ryan, D. A.;
Verma, S. D. Sulfur Lett. 2000, 24, 51.
The proposed reaction pathway for these rhodium-cata-
lyzed deoxygenations involves initial oxidative addition
of HBcat to the metal center,18,19 followed by insertion
of the basic oxygen into the rhodium boron bond (Fig.
2). Reductive extrusion would afford the transient cat-
BOH species, which would react with another equivalent
of HBcat to give dihydrogen and catBOBcat. Unfortu-
nately, we were not able to observe the formation of
HOBcat in these reactions using multinuclear NMR
spectroscopy, even at ꢀ80°C. Further work in this area
will examine the use of HBcat for the deoxygenation of
other heteroatom oxides and will be reported in due
course.
9. In a typical experiment, 3equiv of HBcat in 0.5mL of
C6D6 were added dropwise to a 0.5mL solution of the
appropriate sulfoxide in C6D6 under an atmosphere of
dinitrogen. Reactions were monitored by multinuclear
NMR spectroscopy and products were compared with
known sulfides using GC–MS.
10. (a) Lewis, S. P.; Taylor, N. J.; Piers, W. E.; Collins, S. J.
Am. Chem. Soc. 2003, 125, 14686; (b) Tian, J.; Wang, S.;
Feng, Y.; Li, J.; Collins, S. J. Mol. Catal. A 1999, 144, 137;
(c) Williams, V. C.; Irvine, G. J.; Piers, W. E.; Li, Z.;
Collins, S.; Clegg, W.; Elsegood, M. R. J.; Marder, T. B.
Organometallics 2000, 19, 1619; (d) Stender, M.; Phillips,
A. D.; Power, P. P. Inorg. Chem. 2001, 40, 5314; (e)
Priego, J. L.; Doerrer, L. H.; Rees, L. H.; Green, M. L. H.
Chem. Commun. 2000, 779; (f) Henderson, L. D.; Piers, W.
E.; Irvine, G. J.; McDonald, R. Organometallics 2002, 21,
340.
In summary, catecholborane can be used as a gentle,
efficient, and selective reagent for the deoxygenation of
a wide range of sulfoxides. Although excess HBcat is re-
quired for bulky sulfoxides or sulfoxides containing elec-
tron withdrawing groups, the use of a rhodium catalyst
greatly accelerates these reactions while allowing a min-
imal loading of borane.
Acknowledgements
Thanks are extended to the American Chemical Society-
Petroleum Research Fund (Grant #37824-B1; SAW),
Mount Allison University, the Natural Science and
Engineering Research Council (Canada), the Canada
Research Chairs Program, the Canadian Foundation
for Innovation/Atlantic Innovation Fund, and the Los
Alamos National Laboratory for financial support. We
also thank Dan Durant (MAU), Roger Smith (MAU),
and John Marcone (DuPont) for expert technical assist-
ance and an anonymous reviewer for helpful comments.
11. Carter, C. A. G.; John, K. D.; Mann, G.; Martin, R. L.;
Cameron, T. M.; Baker, R. T.; Bishop, K. L.; Broene, R.
D.; Westcott, S. A. In Group 13 Elements: ACS Sympo-
sium Series; Oxford University Press: Washington, 2002;
p 70.
12. X-ray diffraction data were collected on a Bruker AXS P4/
SMART 1000 diffractometer using x and / scans with a
scan width of 0.3° and 30s exposure times. The detector
distance was 5cm. The data were reduced and corrected
for absorption. The structure was solved by direct
methods and refined by full-matrix least squares on F2.
All nonhydrogen atoms were refined anisotropically.
C14H14B2O6S; Mw = 331.93; monoclinic, space group
Supplementary data
Further details of the crystal structure investigation may
be obtained from the Director of the Cambridge Crys-
˚
P2(1)/c, a = 7.5684(8), b = 8.9369(9), c = 22.318(2) A;