NaIO4/LiBr-mediated diastereoselective dihydroxylation of olefins: A catalytic approach to the prevost-woodward reaction

Article abstract of DOI:10.1021/ol052080n

(Chemical Equation Presented) LiBr catalyzes efficiently the dihydroxylation of alkenes to afford syn and anti diols with excellent diastereoselectivity depending upon the use of NaIO₄ (30 mol %) or PhI(OAc)₂ (1 equiv), respectively, as the oxidants. The oxidation of non-benzylic halides has been achieved for the first time to afford the corresponding diols in excellent yields.

Full text of DOI:10.1021/ol052080n

ORGANIC
LETTERS
2005
Vol. 7, No. 22
5071-5074
NaIO4/LiBr-mediated Diastereoselective
Dihydroxylation of Olefins: A Catalytic
Approach to the Prevost−Woodward
Reaction
Lourdusamy Emmanuvel, Tanveer Mahammad Ali Shaikh, and
Arumugam Sudalai*
Chemical Engineering and Process DeVelopment DiVision,
National Chemical Laboratory, Pashan Road, Pune 411008, India
a.sudalai@ncl.res.in
Received August 29, 2005
ABSTRACT
LiBr catalyzes efficiently the dihydroxylation of alkenes to afford syn and anti diols with excellent diastereoselectivity depending upon the use
of NaIO4 (30 mol %) or PhI(OAc)2 (1 equiv), respectively, as the oxidants. The oxidation of non-benzylic halides has been achieved for the first
time to afford the corresponding diols in excellent yields.
The catalytic dihydroxylation of alkenes represents a unique
method for the preparation of 1,2-diols with defined relative
configuration, and several oxidants are now used for this
purpose both in the laboratory and industry.1 The syn
dihydroxylation of alkenes is most often achieved2 using
OsO4, KMnO4 or RuO4 as catalysts, which add from the less
hindered diastereotopic π-face of alkene. Despite the syn-
thetic utility, the toxicity and high cost of OsO4 and poor
product-selectivity of KMnO4 and RuO4/H2O2 systems have
prevented a successful application of these reagents on
industrial scale. The syn dihydroxylation from the more
hindered π-face can be effected using Woodward’s proce-
dure3 in which alkenes are treated with I2-AgOAc in AcOH
containing water. On the other hand, anti dihydroxylation
of an alkene is generally achieved using certain peroxy acids4
as well as I2-silver benzoate in the absence of water (Prevost
reaction).5 The use of expensive silver salts, a stoichiometric
amount of molecular halogen, and formation of large amount
of organic and inorganic wastes resulted in a search for
simpler systems.6
* Corresponding author. Phone: +91-020-25902174. Fax: +91-20-
25893359.
(1) (a) Hudlicky, M. Oxidations in Organic Chemistry; ACS Monograph
Series 186; American Chemical Society: Washington, DC, 1990; pp 174.
(b) Johnson, R. A.; Sharpless, K. B. In Catalytic Asymmetric Synthesis,
2nd ed.; Ojima, I., Ed.; Wiley-VCH: New York, WeinHein, 2000; p 357.
(c) Haines, A. H. ComprehensiVe Organic Synthesis, 1st ed.; Trost, B. M.,
Fleming, I., Eds.; Pergamon: Oxford, 1991; Vol. 7, p 437.
(2) (a) Criegee, R. Justus Liebigs Ann. Chem. 1936, 522, 75. (b) Criegee,
R.; Marchand, B.; Wannowius, H. Justus Liebigs Ann. Chem. 1942, 550,
99. (c) Schroder, M. Chem. ReV. 1980, 80, 187. (d) Hentges, S. G.;
Sharpless, K. B. J. Am. Chem. Soc. 1980, 102, 4263. (e) Nomura, K.;
Okazaki, K.; Hori, K.; Yoshii, E. J. Am. Chem. Soc. 1987, 109, 3402. (f)
Coleman, J. E.; Ricciuti, C.; Swern, D. J. Am. Chem. Soc. 1956, 78, 5342.
(g) Ogino, T. Tetrahedron Lett. 1980, 21, 177. (h) Weber, W, P.; Shepherd,
J, P. Tetrahedron Lett. 1972, 13, 4907. (i) Ogino, T.; Mochizuki, K. Chem.
Lett. 1979, 4. (j) Plietker, B.; Niggemann, M. J. Org. Chem. 2005, 70, 2402
and references therein. (k) Ho, C. M.; Yu, W.-Y.; Che, C.-M. Angew. Chem.,
Int. Ed. 2004, 43, 3303.
The development of a catalytic version of the Prevost-
Woodward reaction is both challenging and useful to
synthetic chemists. We report herein a new “transition-metal-
free” procedure for the dihydroxylation of alkenes catalyzed
by LiBr and mediated by either NaIO4 or (diacetoxyiodo)-
(3) (a) Woodward, R. B.; Brutcher, F. V. J. Am. Chem. Soc. 1958, 80,
209. (b) Woodward, R. B. U.S. Patent, 2,687,435, 1954. (c) House, H. E.
Modern Synthetic Reactions, 2nd ed.; Benjamin: Menlo Park, CA, 1972;
p 439.
(4) Plesnicar, B. Oxidations in Organic Chemistry; Trahanovsky, W. S.,
Ed.; Academic Press: New York, 1978; Part C, p 211.
(5) (a) Prevost, C. Compt. Rend. 1933, 196, 1129. Prevost, C. Compt.
Rend. 1933, 197, 1661. (b) Prevost, C.; Wiemann, J. Compt. Rend. 1937,
204, 700. (c) Cambie, R. C.; Rutledge, P. S. Org. Synth. 59, 169.
10.1021/ol052080n CCC: $30.25
© 2005 American Chemical Society
Published on Web 09/30/2005

diacetates (3) with the ratio 87:5 in 92% combined yield.
This mixture was subjected to basic hydrolysis (K2CO3,
MeOH, 25 °C) without separation to furnish 1-phenyl-1,2-
ethanediol in 87% yield (Scheme 1). Control experiments
indicated that no dihydroxylation occurred in the absence
of either LiBr or NaIO4.
Scheme 1
To identify a suitable catalytic system, we screened several
halogen sources (KI, NaCl, LiBr, NaBr, Br2, NBS, and
pyHBr3) and found that LiBr had shown remarkable en-
hancement in rate and yield of diol (Table 1). Among other
oxidants screened (entries 8-14), KIO3, Na2S2O8, and
PhI(OAc)2 have exhibited comparable activity as that of
NaIO4. Lowering the amount of LiBr below 20 mol % led
to a sharp decline in the yield of the diol (entry 4). We
determined that 30 mol % of NaIO4, acting both as oxidant
and as a source of water (thus providing “wet” Woodward
condition), is sufficient to convert 1 equiv of styrene to the
corresponding diol.
benzene [PhI(OAc)2], which are quite stable at the reaction
temperature.
Recently, we have reported that the NaIO4/LiBr combina-
tion oxidizes toluene under acidic conditions to benzyl acetate
in excellent yield.7 During our mechanistic investigation, we
further observed that the reaction proceeded through benzyl
bromide and that its rate of solvolysis was enhanced by the
addition of a catalytic amount of NaIO4. Surprisingly, when
(1,2-dibromoethyl)benzene was subjected to this solvolysis,
bromides at benzylic as well as homobenzylic positions
underwent solvolysis to give regioisomers of diol derivative
2a and 2b in excellent yield. Although oxidation of benzylic
bromides by TeO2 has been reported,8 the present protocol
constitutes the first report on the oxidation of non-benzylic
halides, anchimerically assisted by acetyl groups present at
the 2-positions.
Several alkenes (aliphatic, styrenic, allylic, disubstituted
alkenes, R,â-unsaturated alkenes, etc.) with electron-donating
and -withdrawing groups underwent dihydroxylation (Table
2) and produced the corresponding diols in excellent
Table 2. LiBr-Catalyzed Dihydroxylation9 of Olefins Using
a
NaIO4
Encouraged by this result, we envisioned to prepare diol
directly from styrene using a catalytic amount of LiBr (20
mol %) and NaIO4 (30 mol %) in AcOH at 95 °C and indeed
obtained regioisomers of styrene mono- (2a, 2b) and
product
(5)
drb
diol
no.
olefin (4)
syn:anti yield (%)c
1
2
3
4
5
6
7
8
styrene
5a
5b
5c
5d
5e
5f
5g
5h
5i
87
89
90
78d
4-methylstyrene
4-bromostyrene
4-acetoxystyrene
â-methylstyrene
cis-stilbene
Table 1. Effect of Oxidant and Halogen Sources on Catalytic
Dihydroxylation of Styrenea
88:12
99:1
100: 0
98:2
84
87j
79
trans-stilbene
entry
oxidantb
halogen sourcec
yield of diol (%)d
indene
87
79
77
80
1
2
3
4
5
6
7
8
NaIO4
NaIO4
NaIO4
NaIO4
NaIO4
NaIO4
NaIO4
KIO3
NaCl
KI
NaBr
LiBr
NBS
Br2
PyHBr3
LiBr
LiBr
LiBr
LiBr
LiBr
LiBr
LiBr
22
65
84
9
1,2-dihydronaphthalene
cinnamyl alcohol
allyl phenyl ether
methyl trans-cinnamate
4-Cl-R-methylstyrene
vinylcyclohexane
3-buten-1-ol
cis-2-butene-1,4-diol
allyl alcohol
allyl bromide
98:2
10
11
12
13
14
15
16
17
18
19
20
21
5j
5k
5l
85:15i
87 (53)f
79
80:20
92:8
65e
82g
85
5m
5n
5o
5p
5q
5r
5s
5t
82
78
84
42
36
85
77
trace
85
91d
83d,j
86d
79d,h
86f
83
9
V2O5
WO3
10
11
12
13
14
Na2S2O8
oxone
cyclohexene
cyclooctene
1-octene
90:10
85:15
mCPBAe
PhI(OAc)2
5u
84
a Reactions were carried out following ref 9. b Diastereomeric ratios were
determined from 13C NMR and GC. c Isolated yield after chromatographic
purification. d Product was isolated as acetate after acetylation (Ac2O, py).
e Time ) 36 h. f At 80 °C for 36 h. g Hydrolyzed using KOH, MeOH. h 50
mol % of NaIO4 employed. i 1 equiv of water was used (diastereoselectivity
in the absence of water was syn:anti ) 77:23). j Corresponding syn-diol
was formed.
a Reaction conditions: (i) styrene (3 mmol), oxidant (30 mol % to 1
equiv), halogen source (20 mol %), AcOH (5 mL), 95 °C, 18 h; (ii) K2CO3
(4.5 mmol), MeOH (15 mL), 25 °C, 24 h. b NaIO4 ) 30 mol %; KIO3 or
V2O5 or WO3 or Na2S2O8 ) 50 mol %; oxone or mCPBA or PhI(OAc)2 )
1 equiv. c Halogen source ) 20 mol %. d Isolated yield. e m-Chloroper-
benzoic acid. f 10 mol % LiBr employed.
5072
Org. Lett., Vol. 7, No. 22, 2005

yields with syn diastereoselectivity. The syn selectivity is
controlled by water, formed in situ from NaIO4 and AcOH,
which attacks 1,3-dioxolon-2-ylium ion (C) at C-2 position
(Scheme 3).
the LiBr catalyzed dihydroxylation is shown in Scheme 3.
The halogens (X ) I, Br, Cl), generated in situ from alkali
As expected, allyl bromide gave triol due to successive
solvolysis of 1,3-dibromide. Lower yield in the case of R,â-
unsaturated ester may be ascribed to the slower rate of
bromoacetoxylation. However, attempts to obtain anti diols,
by removing water formed in situ using either molecular
sieves (4 Å) or anhydrous MgSO4 were not successful.
Interestingly, anti diols were obtained when PhI(OAc)2 was
employed as the oxidant in stoichiometric amounts under
the same reaction condition. Since no water is formed, acetic
acid acts as the nucleophile and opens up the intermediate
C at C-4 position to result in trans-diastereoselectivity. The
lower selectivity observed in the case of cyclohexene and
â-methylstyrene can be explained in terms of SN2 displace-
ment of bromide in B by LiOAc (Table 3).
Scheme 3. Proposed Catalytic Cycle for Dihydroxylation
Process
Table 3. LiBr-Catalyzed anti-Dihydroxylation of Olefins Using
a
PhI(OAc)2
metal halides by oxidation with NaIO4 or PhI(OAc)2 rapidly
undergo bromoacetoxylation with alkenes via bromonium
ion A to produce trans-1,2-bromoacetate derivative B, which
was isolated and characterized. The intermediate species C,
formed from B in the presence of NaIO4, assisted anchi-
merically11 by the acetate group, is opened either by water
to give cis-hydroxy acetate or by acetic acid to give the trans-
diacetate with concomitant liberation of Br2.
product
(6)
yield of
drc
(anti:syn)
entry
olefin (4)
indene
cis-stilbene
trans-stilbene
cyclohexene
diol (%)b
1
2
3
4
5
6a
6b
6c
6d
6e
79
84
87
82
85
100:0
100:0d
100:0
77:23
33:67
In conclusion, we have developed for the first time a new,
practical, and “metal-free” procedure for the dihydroxylation
(6) (a) Uemura, S.; Ohe, K.; Fukuzawa, S.; Patil, S.; Sugita, N. J.
Organomet. Chem. 1986, 316, 67. (b) Georgoulis, C.; Valery, J. Bull. Soc.
Chim. Fr. 1975, 1431. (c) Georgoulis, C.; Valery, J. Synthesis 1978, 402.
(d) Horiuchi, C. A.; Satoh, J, Y. Bull. Chem. Soc. Jpn. 1987, 60, 426. (e)
Cambie, R. C.; Hayward, R. C.; Roberts, J. L.; Rutledge, P. S. J. Chem.
Soc., Perkin Trans. 1 1974, 1858. (f) Buddrus, J. Angew. Chem., Int. Ed.
Engl. 1973, 12, 163. (g) Corey, E. J.; Das, J. Tetrahedron Lett. 1982, 23,
4217.
â-methylstyrene
a Reactions were carried out following ref 9 but with 1 equiv of
PhI(OAc)2. b Isolated yield after chromatographic purification. c Diastereo-
meric ratios were determined from GC. d The corresponding anti-diol was
formed.
(7) (a) Dewkar, G. K.; Narina, S. V.; Sudalai, A. Org. Lett. 2003, 5,
4501. (b) Shaikh, T. M.; Sudalai, A. Tetrahedron. Lett. 2005, 46, 5589.
(8) Bergman, J.; Engman, L. J. Org. Chem. 1982, 47, 5191.
Our earlier studies7 had shown that 1 equiv of NaIO4 was
sufficient to oxidize 8 equiv of Br- ions, as can be seen from
Scheme 2. Hence, only 30 mol % of NaIO4 was required to
bring about 100% conversion.
From the above facts and the evidence provided by the
cyclic voltammetry10 study, the proposed catalytic cycle for
(9) General Experimental Procedure. A mixture of olefin (3 mmol),
NaIO4 (30 mol %), and LiBr (20 mol %) was taken in a 25 mL round-
bottomed flask, and glacial acetic acid (5 mL) was added. The reaction
mixture was heated at 95 °C (using an oil bath) for 18 h. The light yellow
colored reaction mixture turned purple after completion of the reaction.
The reaction mixture was cooled and then extracted with EtOAc (30 mL ×
3), and the combined organic phase was washed with saturated sodium
thiosulfate solution, water, and aqueous NaHCO3. The organic layer was
dried over anhydrous Na2SO4 and concentrated under reduced pressure to
give crude product, which was subjected to basic hydrolysis without
purification. The hydrolysis was carried out by stirring the reaction mixture
with K2CO3 (1.5 equiv) in methanol (20 mL) at 25 °C for 24 h. After
completion of the reaction, methanol was removed under reduced pressure,
and the reaction mixture was extracted with EtOAc (30 mL × 3). The
combined organic phase was washed with water and brine. The organic
layer was then dried over anhydrous Na2SO4 and concentrated under reduced
pressure to give crude diol, which was purified by column chromatography
packed with silica gel using pet ether and EtOAc (7:3) as eluents to afford
pure diol.
Scheme 2
(10) Cyclic voltammogram is given in Supporting Information.
(11) Only organic halides with acetyl groups at the 2-positions were
oxidized by NaIO4 or PhI(OAc)2. Octyl bromide failed to undergo oxidation
under the same reaction condition. Hence, we believe that neighboring group
participation by the acetate group makes the C-Br bond more polar and
thus facilitating the oxidation process.
Org. Lett., Vol. 7, No. 22, 2005
5073

of alkenes catalyzed by LiBr using commercially available
NaIO4 or PhI(OAc)2 as oxidants in acetic acid to produce
syn or anti diols, respectively. The simplicity, environmental
friendliness and readily accessible reagents make this system
superior to other expensive and toxic Tl(I), Ag(I), Bi(III),
and Hg(II) reagents.6b-d
fellowship, respectively. Authors are thankful to Dr. B. D.
Kulkarni, Head, CE-PD Division, for his constant encourage-
ment.
Supporting Information Available: Experimental pro-
cedures and spectral data for all the compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. L.E. and T.M.S. thank CSIR, New
Delhi and DST, New Delhi for the award of research
OL052080N
5074
Org. Lett., Vol. 7, No. 22, 2005