8018
M. Al-Hashimi et al. / Tetrahedron Letters 47 (2006) 8017–8019
Table 1.
selectivity for sulfoxide prevailed under these conditions
in the other cases including heptyl methyl sulfide. The
VO1–TBHB catalyst was recycled three times without
loss in activity using methyl 3-methylsulfinylmethylpro-
pionate. With the VO1–H2O2 system, all five substrates
had ꢀ99% selectivity for the sulfoxide. The VO1–H2O2
catalyst was successfully recycled three times with thio-
anisole as the substrate.
O
S
Immobilised vanadyl alkyl phosphonate
S
R
R'
R
R'
NaBrO3/ TBHP/ H2O2
Substratea
% Sulfoxideb % Sulfoxide
% Sulfoxide
(Cat)NaBrO3 (VO1)hTBHP (VO1)kH2O2
99c,d
70e,f
99i
99l
S
Ph
The VO1 catalyst has generally shown an impressive
activity (with no detectable leaching of metal)19 for the
selective oxidation of sulfides with the three co-oxidants
used and the results with environmentally clean 30%
aqueous hydrogen peroxide are particularly noteworthy.
S
99
99
Me
6
99e
99
99
S
99e,g
99e
99j
99
99
99
99
99
S
S
Me
Me
CO2Me
OH
References and notes
99e,g
99e
99
S
CN
S
1. Sato, K.; Hyodo, M.; Aoki, M.; Zheng, X. Q.; Noyori, R.
Tetrahedron 2001, 57, 2469–2476, See composite refer-
ences 1 and 2 therein.
2. Wang, Y.; Lente, B.; Espenson, J. H. Inorg. Chem. 2002,
41, 1272–1280.
3. Reddy, T. I.; Varma, R. S. Chem. Commun. 1997, 471–472.
4. Corma, A.; Iglesias, M.; Sanchez, F. Catal. Lett. 1996, 39,
153–156.
5. Fraile, M. J.; Garcia, J. I.; Lazaro, B.; Mayoral, J. A.
Chem. Commun. 1998, 1807–1808.
6. Ayala, V.; Corma, A.; Iglesias, M.; Sanchez, F. J. Mol.
Catal. A. 2004, 221, 201–208.
7. Karimi, B.; Ghoreishi-Nezhad, M.; Clark, J. H. Org. Lett.
2005, 4, 625–628.
8. Kantam, M. L.; Neelima, B.; Reddy, Ch. V.; Chaudhury,
M. K.; Dehury, S. K. Catal. Lett. 2004, 95, 19–22.
9. Maayan, G.; Popovitz-Biro, R.; Neumann, R. J. Am.
Chem. Soc. 2006, 128, 4968–4969.
70f
a See Ref. 14 for Ce1–NaBrO3 and Ce1–TBHP systems.
b Conversions were ꢀ99% by proton NMR; only trace amounts of
residual sulfide were observed and oxidations were generally selective
with only trace amounts of sulfone seen in most cases. Run time was
1 h at room temperature unless otherwise stated.
c
0.03 g catalyst, 1 mmol substrate, 1.5 mmol NaBrO3 in CH3CN
(3 mL), H2O (0.5 mL), room temperature, 1 h (VO1), 4 h (Ni1), 1 h
40 °C (Co1); inactive in the absence of sodium bromate.
d Recycled three times, VO1, 4% over-oxidation in the second recycle.
e
Catalyst is VO1.
f
30% over-oxidation to sulfone observed.
g Reaction time 2 h.
h 0.03 g VO catalyst, 1 mmol substrate, 5 mL acetonitrile, 2 equiv
TBHP 70% in water, 1 h, room temperature.
i
Recycled three times without change; no conversion in the absence of
10. Jurado-Gonzalez, M.; Sullivan, A. C.; Wilson, J. R. H.
Tetrahedron Lett. 2003, 44, 4283–4286.
11. Al-Haq, N.; Sullivan, A. C.; Wilson, J. R. H. Tetrahedron
Lett. 2003, 44, 769–771.
12. Jurado-Gonzalez, M.; Sullivan, A. C.; Wilson, J. R. H. J.
Mater. Chem. 2002, 12, 3605–3609.
TBHP.
j
2 h, recycled three times without change.
k 0.03 g VO1 catalyst, 1 mmol substrate, 5 mL acetonitrile, 2 equiv
H2O2 (30% in water) at room temperature, 1 h.
Recycled three times without change.
l
13. Jurado-Gonzalez, M.; Sullivan, A. C.; Wilson, J. R. H.
Tetrahedron Lett. 2004, 45, 4465–4468.
14. Al-Hashimi, M.; Roy, G.; Sullivan, A. C.; Wilson, J. R. H.
Tetrahedron Lett. 2005, 46, 4365–4368.
the oxidation of thioanisole. For the Co1 catalyst, the
conversion of sulfide to sulfoxide at room temperature
was 80% after 17 h but a complete conversion to the
sulfoxide was achieved in 1 h at 40 °C. It is noteworthy
that the related Ce1–NaBrO3 system was generally less
active at room temperature and heating at 30–50 °C
was required. The vanadyl catalyst VO1 showed ꢀ4%
over-oxidation on the second and third recycles. The
Metal1 catalysts were found to be inactive if the reoxi-
dant bromate was excluded. On the basis of perfor-
mance in this initial study, the VO1–NaBrO3 system
was screened further with a wider range of substrates
and VO1 itself with 70% aqueous TBHP and 30% aque-
ous H2O2 as oxidants. For the other sulfide substrates
examined with VO1–NaBrO3, selective oxidation to
the sulfoxide was observed, except for heptyl methylsul-
fide where there was substantial over-oxidation to the
sulfone. In contrast, the analogous cerium catalysed
reaction run at 40 °C was ꢀ96% selective for the sulfox-
ide.13 For the VO1–TBHB catalyst at room temperature
substantial over-oxidation to the sulfone was observed
for 3-methylthio-1-propene, (no epoxide formed) but
15. Preparation of Metal1 materials. The metal was intro-
duced as VOSO4Æ5H2O, M(NO3)2Æ6H2O, M = Co, Ni;
Cu(NO3)2Æ5H2O. Metal1, was prepared by treating an
aqueous suspension of the disodium phosphonate mate-
rial, Na1, with an aqueous solution of metal compound
(such that phosphonate: metal complex = 1:2). The solids
obtained were filtered, washed with copious amounts of
water and then with ether and finally dried at 100 °C/
0.01 Torr. Metal loading (mmol gÀ1) V 1.08, Co, 1.2 Ni,
1.3 was measured by determining the quantity of metal
released from a known weight of material treated with
conc. nitric acid using atomic absorption spectroscopy.
16. Typical procedures using the Meta11–NaBrO3 system.
The catalyst and sulfide (see Table 1 for quantities) were
added to acetonitrile (3 mL) and then sodium bromate
(0.23 g) and water (0.5 mL) were then added. This mixture
was stirred at the temperature and for the time indicated in
Table 1. The reaction was followed by TLC. The catalyst
was separated by filtration and washed with ethyl acetate.
The combined filtrate and ethyl acetate washings were
then washed with water and the organic phase was