Copper-catalyzed diacetoxylation of olefins using PhI(OAc)2 as oxidant

Article abstract of DOI:10.1021/ol902813m

(Figure Presented) Copper(I) or -(II) salts with weakly coordinating anions catalyze the diacetoxylation of olefins efficiently In the presence of PhI(OAc)₂ as the oxidant under mild conditions. The reaction is effective for aryl, aryl alkyl, as well as aliphatic terminal and internal olefins forming the corresponding vicinal diacetoxy compounds In 70-85% yields and dr (syn/anti) of up to 5.2. Under these conditions, homoallylic alcohols formed the corresponding tetrahydrofuran derivatives in high yields.

Full text of DOI:10.1021/ol902813m

ORGANIC
LETTERS
2010
Vol. 12, No. 7
1412-1415
Copper-Catalyzed Diacetoxylation of
Olefins using PhI(OAc)2 as Oxidant
Jayasree Seayad,* Abdul Majeed Seayad, and Christina L. L. Chai*
Institute of Chemical and Engineering Sciences, 1 Pesek Road, Singapore 627833
jayasree_seayad@ices.a-star.edu.sg; christina_chai@ices.a-star.edu.sg
Received December 7, 2009
ABSTRACT
Copper(I) or -(II) salts with weakly coordinating anions catalyze the diacetoxylation of olefins efficiently in the presence of PhI(OAc)2 as the
oxidant under mild conditions. The reaction is effective for aryl, aryl alkyl, as well as aliphatic terminal and internal olefins forming the
corresponding vicinal diacetoxy compounds in 70-85% yields and dr (syn/anti) of up to 5.2. Under these conditions, homoallylic alcohols
formed the corresponding tetrahydrofuran derivatives in high yields.
Catalytic vicinal dioxygenation of olefins is an extremely
important reaction in the synthesis of high value intermedi-
ates for pharmaceuticals and fine chemicals.1 The OsO4-
catalyzed (or Upjohn) dihydroxylation2 and its enantiose-
lective version, the Sharpless dihydroxylation,3 are among
the most widely used dioxygenation reactions in organic
synthesis. However, the use of expensive and highly toxic
osmium catalysts has limited the use of this technology to
merely synthesis in a small scale. In recent years, there has
been substantial interest in the development of alternative
catalysts for alkene dioxygenations.4 Sudalai et al.5 reported
a metal-free catalytic version of the Woodward-Prevost6
reaction using LiBr as the catalyst. In this reaction, syn and
anti diols with excellent diastereoselectivities were obtained
when NaIO4 or PhI(OAc)2 was used as the oxidant, respec-
tively. Recently, Li et al.7 and Jiang et al.8 independently
reported a Pd-catalyzed diacetoxylation of alkenes to the syn-
1,2-diacetates using PhI(OAc)2 or molecular oxygen as the
oxidants, respectively. In the former case, a cationic pal-
ladium complex with electron-rich diphosphines as ligands
was essential for the reaction, while in the latter case,
Pd(OAc)2 was sufficient to catalyze the transformation
efficiently.
In recent years, the use of copper salts as catalysts has
gained much prominence in organic synthesis due to their
economic attractiveness, good functional group tolerance, and
scalability in large-scale synthetic procedures.9 The peroxy-
disulfate oxidation of aliphatic olefins10 and R- and ꢀ-
(4) Shing, T. K. M.; Tai, V-W. F.; Tam, E. K. W. Angew. Chem., Int.
Ed. 1994, 33, 2312. (b) Shing, T. K. M.; Tam, E. K. W.; Tai, V-W. F.;
Chung, I. H. F.; Jiang, Q. Chem.sEur. J. 1996, 2, 50. (c) Verboom, R. C.;
Plietker, B. J.; Ba¨ckvall, J. E. J. Organomet. Chem. 2003, 687, 508. (d)
Yoshisaki, H.; Ba¨ckvall, J. E. J. Org. Chem. 1998, 63, 9339. (e) Grennberg,
H.; Ba¨ckvall, J. E. J. Chem. Soc., Chem. Commun. 1993, 1331. (f)
Grennberg, H.; Fazon, S.; Ba¨ckvall, J. E. Angew. Chem., Int. Ed. Engl.
1993, 32, 263. (g) Ba¨ckvall, J. E.; Nordberg, R. E. J. Am. Chem. Soc. 1981,
103, 4959.
(1) Hudlicky, M. Oxidations in Organic Chemistry; ACS Monograph
Series 186; American Chemical Society: Washington, DC, 1990; p 174.
(b) Johnson, R. A.; Sharpless, K. B. In Catalytic Asymmetric Synthesis,
2nd ed.; Ojima, I., Ed.; Wiley-VCH: New York, 2000; p 357. (c) Haines,
A. H. In ComprehensiVe Organic Synthesis, 1st ed.; Trost, B. M., Fleming,
I., Eds.; Pergamon: Oxford, 1991; Vol. 7, p 437.
(2) (a) VanRheenen, V.; Kelly, R. C.; Cha, D. Y. Tetrahedron Lett. 1976,
1973. (b) Eames, J.; Mitchell, H.; Nelson, A.; O’Brien, P.; Warren, S.;
Wyatt, P. J. Chem. Soc., Perkin. Trans. 1 1999, 1095.
(5) Emmanuvel, L.; Ali Shaikh, T. M.; Sudalai, A. Org. Lett. 2005, 7,
5071.
(6) (a) Woodward, R. B.; Brutcher, F. V. J. Am. Chem. Soc. 1958, 80,
209. (b) Pre´vost, C. Compt. Rend. 1933, 196, 1129.
(3) (a) Jacobsen, E. N.; Marko, I.; Mungall, W. S.; Schroeder, G.;
Sharpless, K. B. J. Am. Chem. Soc. 1988, 110, 1968. (b) Kolb, H. C.; Van
Nieuwenhze, M. S.; Sharpless, K. B. Chem. ReV. 1994, 94, 2483. (c)
Gonzalez, J.; Aurigemma, C.; Truesdale, L. Organic Syntheses; Wiley: New
York, 2004; Collect. Vol. 10, p 603; Org. Synth. 2002, 79, 93. (d) Johnson,
R. A.; Sharpless, K. B. In Catalytic Asymmetric Synthesis, 2nd ed.; Ojima,
I., Ed.; VCH: New York, 2000.
(7) Li, Y.; Song, D.; Dong, V. M. J. Am. Chem. Soc. 2008, 130, 2962.
(8) Wang, A.; Jiang, H.; Chen, H. J. Am. Chem. Soc. 2009, 131, 3846.
(9) (a) Hideki, Y.; Koichiro, O. Angew. Chem., Int. Ed. 2005, 44, 4435.
(b) Ken-ichi, Y.; Kiyoshi, T. Chem. ReV. 2008, 108, 2874. (c) Punniya-
murthy, T.; Rout, L. Coord. Chem. ReV. 2008, 252, 134. (d) Olafs, D.;
Hien-Quang, D.; Dmitry, S. Acc. Chem. Res. 2009, 42, 1074.
10.1021/ol902813m  2010 American Chemical Society
Published on Web 03/11/2010

optimum CH2Cl2-AcOH ratio of 3:1 at 40 °C using 1.3
equiv of PhI(OAc)2 (entry 5, Table 1). Alternatively, a 3:1
mixture of acetonitrile-AcOH could also be used as solvent
without compromising the reaction yields. It is noted from
entry 4 in Table 1 that this reaction can also be carried out
at rt without significant variation in the yield of the desired
product 2a. Screening of other copper precursors showed
that both copper(I) and copper(II) salts with weakly coor-
dinating anions such as -OTf (entries 1-8, Table 1) and
-BF4 (entry 9, Table 1) were effective in the catalysis, while
Table 1. Copper-Catalyzed Diacetoxylation of Styrene:
Optimization Studies
entry
catalyst
Cu(OTf)2
solvent
CH2Cl2
yield of 2aa (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
68b
78c
traced
78e
85
80f
80
81
77
-
-
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
AcOH
those with strongly coordinating OAc (entries 10 and 11,
Table 1) and Cl- (entry 12, Table 1) ions were totally inactive
under these conditions. In control reactions without any
copper catalyst, but with the oxidant and vice versa, no
conversion of styrene was observed (entries 13 and 14, Table
1).
AcOH-H2O (1:1)
CH2Cl2-AcOH (3:1)
CH2Cl2-AcOH (3:1)
CH2Cl2
CH3CN-AcOH (3:1)
CH2Cl2-AcOH (3:1)
Cu(CH3CN)4BF4 CH2Cl2-AcOH (3:1)
Cu(OAc)2
CuOAc
CuCl
CH2Cl2-AcOH (31)
CH2Cl2-AcOH (3:1)
CH2Cl2-AcOH (3:1)
CH2Cl2-AcOH (3:1)
CH2Cl2-AcOH (3:1)
-
-
Scheme 1
.
Proposed Mechanism of Copper-Catalyzed
Diacetoxylation of Olefins
-
-
g
Cu(OTf)2
a GC yield, determined using dodecane as an internal standard. b Side
products such as 2-phenylethane-1,1-diyl diacetate and styrene dimers were
detected by GC-MS. c Small amount of benzaldehyde was detected by
GC-MS. d Hydroxyacetates 5a and 6a (Scheme 1) and a major amount of
benzaldehyde were detected by GC-MS. e At rt. f In the presence of 3 equiv
of acetic acid with respect to styrene. g Reaction without PhI(OAc)2.
alkenylbenzenes11 to the corresponding allylic acetates and
glycol diacetates, respectively, were known to be catalyzed
by cupric acetate in acetic acid under reflux conditions. It
was also reported that cupric nitrate, triflate,12 and binuclear
Cu(II) complexes can catalyze the oxidation of olefins to
epoxides in the presence of iodosylbenzene as the oxidant.13
To our knowledge, a general and efficient copper-catalyzed
methodology for the dioxygenation of olefins to the corre-
sponding diols or derivatives has not been developed to date.
We report herein a mild and efficient copper-catalyzed vicinal
diacetoxylation of olefins using PhI(OAc)214 as the oxidant.
In our initial experiments, we found that Cu(II) triflate
catalyzes the vicinal diacetoxylation of styrene in the
presence of PhI(OAc)2 as the oxidant to form 1-phenyle-
thane-1,2-diyl diacetate efficiently. Traces of geminal diac-
etoxylation product were also detected by GC-MS. Small
amounts of benzaldehyde15 were formed when the reaction
was carried out in acetic acid as solvent or in the presence
of acetic acid/water mixture (entries 2 and 3, Table 1). This
byproduct formation was minimized by adjusting the solvent
system and optimizing the reaction conditions. Thus, the best
yields of the 1,2-diacetoxylated product was obtained at an
The proposed mechanism for the copper-catalyzed diac-
etoxylation reaction is outlined in Scheme 1. When the
Cu(OTf)2-catalyzed diacetoxylation of styrene (1a) was
monitored by GC-MS, small amounts of hydroxyacetates
(5a and 6a in Scheme 1, R1, R2 ) Ph, H) along with the
1,2-diacetate 2a were observed as intermediates. These
hydroxyacetates 5a and 6a were completely converted to the
diacetate 2a after 16 h. The detection of 5a and 6a in the
reaction suggests the formation of an acetoxonium ion A as
the intermediate.7,11b This in turn could be formed via a
Cu(III)-Cu(I) catalytic cycle12,13,16 as shown in Scheme 1.17
The Cu(II)(OTf)2 is oxidized to the active Cu(III)(OAc)2-
(OTf) by the oxidant PhI(OAc)2 which then coordinates and
inserts olefin forming the intermediate species iii and iv.
Release of A from iv by a SN2-type reductive elimination
leads to Cu(I)OTf, which is oxidized back to the active
Cu(III) species ii by PhI(OAc)2. The reaction of the
intermediate A with acetic acid will then lead to the
(10) Arnodi, C.; Citterio, A.; Minisci, F. J. Chem. Soc., Perkin Trans.
2 1983, 531.
(11) (a) Citterio, A.; Arnodi, C. J. Chem. Soc., Perkin Trans. 1 1983,
891. (b) Dobson, P.; Norman, J. A.; Thomas, C. B. J. Chem. Soc., Perkin
Trans. 1 1986, 1209.
(12) (a) Franklin, C. C.; VanAtta, R. B.; Tai, A. F.; Valentine, J. S.
J. Am. Chem. Soc. 1984, 106, 814. (b) VanAtta, R. B.; Franklin, C. C.;
Valentine, J. S. Inorg. Chem. 1984, 23, 4121.
(15) Benzaldehyde could be formed by the oxidative cleavage of the
hydroxyacetate intermediates 5a and 6a (see ref 11b).
(16) (a) Chemler, S. R.; Fuller, P. H. Chem. Soc. ReV 2007, 36, 1153,
and references cited therein. (b) Zabawa, T. P.; Kasi, D.; Chemler, S. R.
J. Am. Chem. Soc. 2005, 127, 11250.
(13) Tai, A. F.; Margerum, L. D.; Valentine, J. S. J. Am. Chem. Soc.
1986, 108, 5006.
(14) Stang, P. J.; Zhdankin, V. V. Chem. ReV. 1996, 96, 3, 1123.
Org. Lett., Vol. 12, No. 7, 2010
1413

formation of the diacetoxylated product 2a while trace
amounts of extrinsic water that may be present in the solvent
give rise to the hydroxyacetates 5a and 6a which are
subsequently acylated in the presence of Cu(III) or any Cu(II)
species present in the reaction mixture, leading to 2a. The
acylation of alcohols by Cu(OTf)2 in acetic acid has been
reported previously.18
excellent yields. While the aryl olefins reacted efficiently at
40 °C, aryl alkyl and alkyl olefins required a slightly higher
temperature (80 °C) for the reaction to proceed. In the case
of 4-substituted styrene derivatives, i.e., 4-methylstyrene (1b),
4-chlorostyrene (1c), and 4-vinylbenzoic acid (1f), the yields
were 75%, 82%, and 70%, respectively. 2- and 3-bromosty-
renes (1d and 1e) and 2-vinylnaphthalene (1g) were also
reactive substrates giving rise to 75%, 79%, and 72% yields
of the desired products, respectively. It is noteworthy that,
under our conditions, allyl benzene (1h) and 1-octene (1i)
yielded the corresponding 1,2-diacetate products (2h and 2i)
in excellent yields (82% and 85% at 80 °C in acetic acid as
the solvent). This is in contrast to reports of the peroxydis-
ulfate oxidation which gave the corresponding allylic acetates
or 1,2,3-triacetates as the major products.10
Table 2. Copper-Catalyzed Diacetoxylaton of Terminal Olefins
Table 3. Copper-Catalyzed Diacetoxylation of Internal Olefins
a
Diastereomeric ratio detemined by H NMR spectroscopy. b Isolated
1
yield. c At 80 °C with AcOH as solvent.
The diacetoxylation of internal olefins was also investi-
gated, and to our delight, the reaction proceeded in good
yields albeit with moderate diastereoselectivities (Table 3).
The “best” conditions for these reactions were found to use
CH2Cl2-AcOH (1:1) as solvent at 40 °C. In the case of
trans-stilbene (3a), a yield of 71% and a syn/anti ratio of
5.2 were observed under these conditions. Indene (3b) and
1,2-dihydronaphthalene (3c) gave the corresponding 1,2-
diacetates 4b and 4c in 78% and 75% yields and a dr of 3
and 1, respectively. Methyl cinnamate (3d) only yielded trace
amounts of the diacetoxylation product at 40 °C; however,
at 80 °C in acetic acid as solvent the 1,2-diacetate product
(4d) was obtained in 70% yield with a dr of 1.8.
a Isolated yield. b At 80 °C in AcOH as solvent.
After achieving an optimized catalyst system, we studied
the generality of this method with other olefins. As shown
in the Table 2, this methodology can be extended to a number
of aryl (1a-g), aryl alkyl (1 h), and alkyl (1i) terminal olefins
to yield the corresponding 1,2-diacetates (2a-i) in good to
(17) The ESI-TOF-MS(+) analysis of a stoichiometric reaction of
Cu(OTf)2, PhI(OAc)2, and styrene in AcOH indicated the formation of the
species (iv-a + Na, m/z ) 457) and (iii-a + Na-HOTf, m/z ) 307). along
with (2a + Na, m/z ) 245) (R1, R2 ) Ph, H) (see the Supporting
Information).
(18) Chandra, K. L.; Saravanan, P.; Singh, R. K.; Singh, V. K.
Tetrahedron 2002, 58, 1369.
The reaction of homoallylic alcohol derivatives 7a-d with
PhI(OAc)2 in AcOH in the presence of Cu(OTf)2 at 80 °C
gave the corresponding tetrahydrofuran derivatives 9a-d
(Table 4), plausibly via the 5-exo-tet-cyclization of the
1414
Org. Lett., Vol. 12, No. 7, 2010

1,2,4-triyl triacetate (10a, R, R1 ) Ph, H) were also isolated
from the reaction with 1-phenylbut-3-en-1-ol (7a). This could
arise from the copper-catalyzed acylation of the intermediate
8a (R, R1 ) Ph, H) as shown in Scheme 2.
Table 4. Formation of Tetrahydrofuran Derivatives by
Copper-Catalyzed Oxidation of Homoallylic Alcohols using
PhI(OAc)2
Scheme 2
.
Proposed Formation of Tetrahydrofuran Derivatives
from Homoallylic Alcohols
In conclusion, we have developed a simple and efficient
copper-catalyzed diacetoxylation of olefins to the corre-
sponding vicinal diacetoxy compounds under mild condi-
tions. This methodology is applicable to aryl and aliphatic
olefins as well as terminal and internal olefins and provides
good yields and moderate diastereoselectivities. Under these
conditions, homoallylic alcohols formed the corresponding
tetrahydrofuran derivatives efficiently. Further studies di-
rected toward an enantioselective variant are underway.
a Diastereomeric ratio determined by GC analysis and 1H NMR
spectroscopy. b Isolated yield.
intermediate A′ or 8 as shown in Scheme 2.19 Thus, aryl
and alkyl secondary alcohols 7a (R, R1 ) Ph, H), 7b (R, R1
) 4-CF3Ph, H), and 7d (R, R1 ) Cy, H) gave the
tetrahydrofuran derivatives 9a, 9b, and 9d in 78-82% yield
and a dr of 1-1.3 (Table 4). The tertiary alcohol 2-phenyl-
pent-4-en-2-ol (7c) also reacted in a similar manner to form
9c in 78% yields (dr 1.4). Small amounts of 4-phenylbutane-
Acknowledgment. This work is funded by the Institute
of Chemical and Engineering Sciences (Science and Engi-
neering Research Council, Agency for Science, Technology
and Research, Singapore).
Supporting Information Available: Experimental pro-
cedures and compound characterization data; NMR spectra.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(19) Experiments using O-benzylated 8a (R ) Ph, R1 ) H; compound
S-2 in the Supporting Information) indicate the possibility of a copper-
catalyzed cyclization to form 9a under oxidative conditions (see the
Supporting Information).
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