Bromamine-T as an efficient amine source for Sharpless asymmetric aminohydroxylation of olefins

Article abstract of DOI:10.1016/j.tetlet.2013.12.002

Asymmetric aminohydroxylation of various olefins was carried out using bromamine-T as nitrogen source in the presence of (DHQ)₂PHAL ligand. The new nitrogen source has been found to be effective in terms of yield and reaction time. The optical purities of the products could be obtained with up to 99% ee.

Full text of DOI:10.1016/j.tetlet.2013.12.002

Tetrahedron Letters 55 (2014) 713–715
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Bromamine-T as an efficient amine source for Sharpless asymmetric
aminohydroxylation of olefins
⇑
Arun Jyoti Borah, Prodeep Phukan
Department of Chemistry, Gauhati University, Guwahati 781014, Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Asymmetric aminohydroxylation of various olefins was carried out using bromamine-T as nitrogen
source in the presence of (DHQ)2PHAL ligand. The new nitrogen source has been found to be effective
in terms of yield and reaction time. The optical purities of the products could be obtained with up to
99% ee.
Received 16 September 2013
Revised 29 November 2013
Accepted 2 December 2013
Available online 8 December 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Sharpless asymmetric aminohydroxylation
Bromamine-T
Potassium osmate
(DHQ)2PHAL
Olefin
Vicinal amino alcohols are very important structural motif in
synthetic chemistry due to its occurrence in natural products, chiral
reagents, and asymmetric catalysts. While there are a wide variety
of synthetic routes to this functional group,1 Sharpless asymmetric
aminohydroxylation (AA) reaction remains the most powerful
method for the stereospecific generation of vicinal amino alcohols
from alkenes.2 Since the discovery of the AA method by Sharpless
and co-workers,3 there have been a number of reports for improve-
ment of the procedure,2 The AA process has been successfully per-
Although development of tethered aminohydroxylation (TA)11
gives secure regiochemistry, this reaction occurs without apprecia-
ble influence of chiral ligands and hence failed to give the same lev-
els of enantioselectivity. Development of new nitrogen sources,
new ligands, improved reaction conditions, and understanding of
catalyst–substrate interactions have increased the scope and syn-
thetic utility of the AA process. N-Bromo,N-sodio-p-toluenesulfon-
amide (bromamine-T) has been found to be superior to
chloramines-T as nitrogen source for various organic transforma-
tions.12 However, no study has been reported so far, on the use of
bromamine-T for AA process. As a continuation of our work on
asymmetric aminohydroxylation,13 we report herein our experi-
mental results on the use of bromamine-T as nitrogen source for
the Sharpless’s protocol (Scheme 1).
formed with
a
variety of nitrogen sources, including
6
sulfonamides,3,4 amides,5 carbamates, and aminoheterocycles.7
Most N-halogenated oxidants used in the AA are prepared in situ
by N-chlorination with tert-butyl hypochlorite in the presence of
a base, however some of them are commercially unavailable. Re-
cently Luxenburger and co-workers8 and Castle group9 had re-
ported
a base-free aminohydroxylation of substituted and
functionalized alkene using benzoyloxycarbamates as the nitrogen
source. Although it is possible to achieve excellent enantioselectiv-
ity in aminohydroxylation process by suitable choice of ligands, set-
ting of a particular regioselectivity remains a challenging task,
particularly for unsymmetrical alkene. The problem of regioselec-
tivity is a complex one and many factors have been invoked to ex-
plain observed trends, such as alkene substitution, alkene
polarization, ligand–substrate interactions, steric and electronic
contributions of the ligand, and hydrophobic effects due to the sol-
vent etc.10 These are often mutually dependent on each other.
O
S
Na
N
O
NHTs
R/
Br
R/
R
R
K2OsO2(OH)4 (4 mol%)
(DHQ)2PHAL (5 mol%)
BuOH:H2O (1:1)
OH
R, R/= aryl,
alkyl
t
N
N
N
H
N
H
O
O
H
H
MeO
OMe
N
N
(DHQ)2PHAL
⇑
Corresponding author.
E-mail address: pphukan@yahoo.com (P. Phukan).
Scheme 1. Sharpless asymmetric aminohydroxylation using bromanine-T.
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.12.002

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A. J. Borah, P. Phukan / Tetrahedron Letters 55 (2014) 713–715
Bromamine-T was prepared from chloramine-T following the
After gaining success in case of trans-stilbene, the process was
extended to a variety of olefins which are summarized in Table 1.
Cyclohexene (Table 1, 2a) also responded very well under the reac-
literature procedure.12a,14 We have evaluated the potential of the
reagent using (DHQ)2PHAL ligand which is most widely used for
AA process. Initially we have chosen trans-stilbene (Table 1, 1a)
as the model substrate to carry out the AA process following the
experimental procedure identical to the original catalytic AA pro-
cess.3 When trans-stilbene was subjected to aminohydroxylation
at room temperature,15 occurrence of the reaction was indicated
by a distinct color change from dark green to light yellow. The
reaction was carried out by adding bromanine-T and K2OsO2(OH)4
successively to a solution of (DHQ)2PHAL and trans-stilbene in a
tion condition.
a,b-Unsaturated esters such as cinnamates and
acrylates underwent aminohydoxylation with excellent regioselec-
tivity. These compounds produced b-amino regiomer predomi-
nantly with good yield and with high optical purity (up to 99%
ee). However, ee of the aminohydroxylation product of ethyl-4-
fluoro-cinnamate was found to be low (61%). Styrene (Table 1, 8a)
produced low optical yield (38% ee) under this reaction condition.
Literature search revealed that aminohydroxylation of styrene
using chloramine-T in the presence of cinchona alkaloid ligand
has not been reported before. However, the use of N-sulfonyl-
t
1:1 mixture of BuOH and H2O at room temperature. After 2 h of
reaction at room temperature, the reaction mixture was subjected
to usual work-up procedure. Our preliminary analysis using TLC
indicated the formation of single product. However, further analy-
sis of the crude reaction mixture was not carried out using spec-
troscopy or HPLC. Finally, the crude product was purified using
flash chromatography to get the pure amino alcohol. The reaction
time (2 h) was found to be far better in comparison to that with
chloramine-T (14 h).3 Enantiomeric purity of the recrystallized
product 1b (Table 1) was found to be 62%, which was determined
by HPLC method.
a,b-hydroxyamino acid based ligands and chloramine-T for
aminohydroxylation of styrene resulted in poor yield as well as
ee values.4c Later, Sharpless et al. found that the use of N-halo
carbamates for similar substrates could produce aminoalcohols
with high ee values.6a However yields were found to be low
(ꢀ60%) in this case.
We have further extended the process to 1-octene (Table 1, 9a).
Enantiomeric purity of the resulting product was found to be poor
(40% ee) as determined by chiral HPLC analysis. The time
requirement for the reaction in all cases was found to be better
Table 1
Catalytic asymmetric aminohydroxylation reaction with bromamine-T as the nitrogen sourcea
Yieldb (%)
eec
62
½ ꢁ
a 2D6
d
Entry
Substrate
Product
T (h)
NHTs
1
2
60
ꢂ14.3
OH
1b
1a
NHTs
2
3
1
2
70
60
99
99
+ 2.1
2a
OH
NHTsO
2b
O
ꢂ22.0
OEt
OEt
3a
OH
3b
EtO
O
OH
EtO
NHTs
4
5
1.5
2
75
70
99
99
ꢂ3.1
4a
O
4b
O
NHTsO
OEt
5a
OEt
ꢂ26.7
OH
5b
NHTsO
O
OEt
OEt
6
7
0.5
1
75
72
99
61
+28.5
+16.4
OH
MeO
MeO
F
6b
6a
O
NHTsO
OH
OEt
OEt
F
7b
9b
OH
7a
NHTs
8
9
1
62
72
38
40
+28.6
+7.5
8a
8b
NHTs
1.5
OH
9a
a
b
c
Reactions were carried out in tBuOH/H2O (1:1) using 4 mol % K2OsO2(OH)4 and 5 mol % (DHQ)2PHAL ligand.
Isolated yield.
Enatiomeric excess of the recrystallized product was determined by HPLC.
Specific rotation values with respect to recrystallized product except entry 9.
d

A. J. Borah, P. Phukan / Tetrahedron Letters 55 (2014) 713–715
715
6. (a) Li, G.; Angert, H. H.; Sharpless, K. B. Angew. Chem., Int. Ed. 1996, 35, 2813; (b)
O’Brien, P.; Osborne, S. A.; Parker, D. D. Tetrahedron Lett. 1998, 39, 4099; (c)
O’Brien, P.; Osborne, S. A.; Parker, D. D. J. Chem. Soc. Perkin Trans. 1 1998, 2519;
(d) Reddy, K. L.; Sharpless, K. B. J. Am. Chem. Soc. 1998, 120, 1207; (e) Reddy, K.
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Dress, K. R.; Goossen, L. J.; Liu, H.; Jerina, D. M.; Sharpless, K. B. Tetrahedron Lett.
1998, 39, 7669.
in comparison to the chloramine-T mediated aminohydroxylation
process.3 All the products were isolated with good yields
(60–75%). All the products were recrystallized (except entry 9,
Table 1) and enantiomeric purity was determined via HPLC
analysis. Optical purities of corresponding aminoalcohols are
comparable to those reported earlier.
In conclusion we have examined the suitability of bromamine-T
for Sharpless asymmetric aminohydroxylation of olefins. The new
nitrogen source is effective in terms of yield and reaction time of
the process. The present method is highly regioselective and
products are obtained with moderate to high optical purities. The
present work had shown potentiality as new nitrogen source for
the catalytic AA process.
8. Harris, L.; Mee, S. P. H.; Furneaux, R. H.; Gainsford, G. J.; Luxenburger, A. J. Org.
Chem. 2011, 76, 358.
9. Ma, Z.; Naylor, B. C.; Loertscher, B. M.; Hafen, D. D.; Li, J. M.; Castle, S. L. J. Org.
Chem. 2012, 77, 1208.
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Han, H.; Cho, C.-W.; Janda, K. D. Chem. Eur. J. 1999, 5, 1565; (c) Morgan, A. J.;
Masse, C. E.; Panek, J. S. Org. Lett. 1999, 1, 1949; (d) Harding, M.; Bodkin, J. A.;
Issa, F.; Hutton, C. A.; Willis, A. C.; McLeod, M. D. Tetrahedron 2009, 65, 831; (e)
Bodkin, J. A.; Bacskay, G. B.; McLeod, M. D. Org. Biomol. Chem. 2006, 6, 2544.
11. (a) Donohoe, T. J.; Johnson, P. D.; Cowley, A.; Keenan, M. J. Am. Chem. Soc. 2002,
124, 12934; (b) Donohoe, T. J.; Johnson, P. D.; Pye, R. J. Org. Biomol. Chem. 2003,
1, 2025; (c) Donohoe, T. J.; Johnson, P. D.; Pye, R. J.; Keenan, M. Org. Lett. 2004, 6,
2583; (d) Kenworthy, M. N.; McAllister, G. D.; Taylor, R. J. K. Tetrahedron Lett.
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Acknowledgments
Financial Support from DST (Grant No. SR/S1/OC-43/ 2011),
India is gratefully acknowledged. A.J.B. thanks CSIR for senior
research fellowship.
Supplementary data
12. (a) Vyas, R.; Chanda, B. M.; Bedekar, A. V. Tetrahedron Lett. 1998, 39, 4715; (b)
Antunes, A. M. M.; Marto, S. J. L.; Branco, P. S.; Prabhakar, S.; Lobo, A. M. Chem.
Commun. 2001, 405; (c) Chanda, B. M.; Vyas, R.; Bedekar, A. V. J. Org. Chem.
2001, 66, 30; (d) Vyas, R.; Gao, G.-Y.; Harden, J. D.; Zhang, X. P. Org. Lett. 2004, 6,
1907; (e) Gao, G.-Y.; Harden, J. D.; Zhang, X. P. Org. Lett. 2005, 7, 3191.
13. (a) Phukan, P.; Sudalai, A. Tetrahedron: Asymmetry 1998, 9, 1001; (b) Nandanan,
E.; Phukan, P.; Pais, G. C. G.; Sudalai, A. Indian J. Chem. 1999, 38B, 287; (c)
Phukan, P.; Sudalai, A. Indian J. Chem. 2000, 39B, 291; (d) Phukan, P. Indian J.
Chem. 2002, 41B, 1015; (e) Phukan, P. Indian J. Chem. 2003, 42B, 921.
14. Nair, C. G. R.; Lalithakumari, R.; Senan, P. I. Talanta 1978, 25, 525.
15. General experimental procedure for AA: To a solution of (DHQ)2PHAL (0.039 g,
0.05 mmol, 5 mol %) in tBuOH (2 mL) and water (2 mL) in a round-bottomed
flask were added alkene (1 mmol), bromamine-T (0.816 g, 3 mmol, 3 equiv),
and K2OsO2(OH)4 (0.014 g, 0.04 mmol, 4 mol %). Over the course of the
reaction, the color changed from brown to deep green and then to yellow.
After addition of aqueous sodium sulfite, the phases were separated and the
aqueous phase was extracted with ethyl acetate. The extracts were washed
with brine and dried over anhydrous sodium sulfate and concentrated to
dryness to give the crude product. In some cases (entries 1, 2 and 6), the
reaction became slurry, the products were isolated by filtration. Otherwise, the
crude products were purified by flash column chromatography using
petroleum ether and ethyl acetate as eluent.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.1
2.002.
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