Boronic acid-catalyzed selective oxidation of 1,2-diols to α-hydroxy ketones in water

Article abstract of DOI:10.1002/adsc.201300961

The activation of 1,2-diols through formation of boronate esters was found to enhance the selective oxidation of 1,2-diols to their corresponding α-hydroxy ketones in aqueous medium. The oxidation step was accomplished using dibromoisocyanuric acid (DBI) as a terminal chemical oxidant or an electrochemical process. The electrochemical process was based on the use of platinum electrodes, methylboronic acid [MeB(OH)₂] as a catalyst and bromide ion as a mediator. Electro-generated OH^- ions (EGB) at the cathode acted as a base and "Br⁺" ion generated at the anode acted as an oxidant. Various cyclic and acyclic 1,2-diols as substrates were selectively oxidized to the corresponding α-hydroxy ketones via their boronate esters by the two oxidative methods in good to excellent yields.

Full text of DOI:10.1002/adsc.201300961

COMMUNICATIONS
DOI: 10.1002/adsc.201300961
Boronic Acid-Catalyzed Selective Oxidation of 1,2-Diols to
a-Hydroxy Ketones in Water
Julius M. William,a Masami Kuriyama,a and Osamu Onomuraa,*
a
Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki, Japan
Fax : (+81)-95-819-2476; phone: (+81)-95-819-2429; e-mail: onomura@nagaski-u.ac.jp
Received: October 29, 2013; Published online: February 20, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300961.
Abstract: The activation of 1,2-diols through forma-
tion of boronate esters was found to enhance the
selective oxidation of 1,2-diols to their correspond-
ing a-hydroxy ketones in aqueous medium. The oxi-
dation step was accomplished using dibromoisocya-
nuric acid (DBI) as a terminal chemical oxidant or
an electrochemical process. The electrochemical
process was based on the use of platinum electro-
des, methylboronic acid [MeB(OH)2] as a catalyst
and bromide ion as a mediator. Electro-generated
OHÀ ions (EGB) at the cathode acted as a base
and “Br+” ion generated at the anode acted as an
oxidant. Various cyclic and acyclic 1,2-diols as sub-
strates were selectively oxidized to the correspond-
ing a-hydroxy ketones via their boronate esters by
the two oxidative methods in good to excellent
yields.
backs, such as relatively low yields and side reactions
associated with C C bond cleavage. In this regard,
[9]
À
our group has selectively oxidized 1,2-diols using both
chemical[11] and electrochemical[11a,12] methods with
Me2SnCl2 and CuCl2 catalysts in organic solvents. The
current clean synthesis paradigm prefers the use of
aqueous media. Since water is non-toxic and non-
flammable, its application results in safer and cheaper
processes.[13] In an effort to make this process more
environmentally benign, we recently achieved the se-
lective oxidation of 1,2-diols in water using both
chemical[14] and electrochemical oxidation[15] mediated
by Me2SnCl2 catalyst. The catalyst activates the 1,2-
diol moiety through stannylene acetal formation in
addition to enhancing selectivity for both oxidation
and benzoylation reactions.[16] However, serious issues
have been raised on the toxicity of organotin catalysts
to humans and the environment.[17] Thus, there is
urgent need to search for safer alternatives to organo-
tin catalysts.
Keywords: boronic acids; 1,2-diols; a-hydroxy ke-
tones; selective oxidation; water
Boronic acids, widely used in the Suzuki cross-cou-
pling,[18–20] are known to bind with compounds con-
taining diol moieties with high affinities through re-
versible ester formation (Scheme 1).[21]
Green chemistry has become a central paradigm, in
Such a tight binding of boronic acids to diols allows
both academia and industry. Without this approach, their useful application in saccharide sensing.[22] Re-
industrial chemistry is not sustainable.[1] The develop- cently, our group has utilized boronic acids to activate
ment of environmentally benign synthetic methods
for the oxidation of alcohols is important for organic
synthesis.[2] In particular, the selective synthesis of a-
hydroxy ketones from 1,2-diol precursors is an impor-
tant research focus in the pharmaceutical industry. a-
Hydroxy ketone units are common in antitumor anti-
biotics like olivomycin A,[3] and natural products such
as kurasoin A and B.[4] In addition, a-hydroxy ketones
can conveniently be converted to amino alcohols. The
effective synthetic generation of hydroxyl ketones has
thus been a long standing research focus for many or-
ganic chemists. Various oxidants and Lewis acids have
been used to activate the 1,2-diol moiety.[5–10] Unfortu-
nately, some of the methods developed suffer draw- Scheme 1. Boronate ester formation.
934
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 934 – 940

COMMUNICATIONS
Boronic Acid-Catalyzed Selective Oxidation of 1,2-Diols
Table 1. Optimization study for the selective oxidation of 1a.
Table 2. Screening of boronic acid catalysts.
Entry Variation from the “standard” condi-
tions
Yield
[%][a]
Entry
R in R-B(OH)2
Yield [%][a]
1
2
3
4
5
6
7
none
99
<1
88
52
40
1
2
3
4
5
6
7
8
4-MeOC6H4
2-MeOC6H4
3-MeOC6H4
3,4-(MeO)2C6H3
4-FC6H4
4-MeC6H4
4-CNC6H4
3-NO2C6H4
3-BrC6H4
3-ClC6H4
99
97
98
93
88
94
82
80
91
90
87
91
31
85
61
77
99
99
absence of 4-MeOC6H4B(OH)2
0.05 equiv. of 4-MeOC6H4B(OH)2
absence of K2CO3
DBDMH[b] (1.5 equiv.) instead of DBI
NBS (2.0 equiv.) instead of DBI
Br2 (1.5 equiv.) instead of DBI
15
<1
[a]
[b]
Isolated yield.
1,3-Dibromo-5,5-dimethylhydantoin.
9
10
11
12
13
14
15
16
17
18
4-CF3C6H4
Ph
the 1,2-diol moiety in the monolkylation of 1,2-diols
in organic solvent.[23] The safety of boronic acids, their
ease in handling, good solubility in water and the
availability of a wide variety of boronic acid catalysts,
prompted us to test them for the activation of 1,2-
diols in water. To the best of our knowledge, no previ-
ous report on the selective oxidation of 1,2-diols in
water aided by boronic acid catalysts has been pre-
sented. We began our investigation on the catalytic
4-dibenzothiophene
2-naphthalene
3-biphenyl
3-quinoline
3-methyl-2-buten-2-yl
Me
[a]
Isolated yield.
selective oxidation of 1,2-diols in water using cis-cy- their MeO-substituted counterparts (entries 5–12). Di-
clooctane-1,2-diol 1a as a model substrate and halo- benzothiophene-, naphthalene-, biphenyl- and quino-
gen cation “source” oxidants. After a series of optimi- lineboronic acids were also tried, but resulted in low
zation studies, we found that selective oxidation of 1a yields of the desired products (entries 13–16). Inter-
in water proceeded efficiently in the presence of estingly, simple alkyl and alkenylboronic acids, such
10 mol% of 4-MeOC6H4B(OH)2, 1.0 equiv. of potassi- as 3-methyl-2-buten-2-ylboronic acid and MeB(OH)2
um carbonate, and 1.0 equiv. of DBI[24] at a low tem- gave excellent yields, comparable to those obtained
perature (08C) under dark conditions within 1 h to with 4-MeOC6H4B(OH)2 (entries 17 and 18).
afford 2a in 99% yield (entry 1, Table 1).
With the three best catalysts namely, MeB(OH)2, 4-
Selective oxidation did not proceed in the absence MeOC6H4B(OH)2 and 3-methyl-2-buten-2-ylboronic
of the catalyst (entry 2). This demonstrates the impor- acid, we next explored the substrate applicability to
tant role played by the catalyst in the activation of the oxidation system involving K2CO3 as a base and
the 1,2-diol moiety. Reducing the catalyst loading to DBI as
a
terminal oxidant. Generally, both
0.05 equiv. as well as performing the reaction in the MeB(OH)2 and 4-MeOC6H4B(OH)2 catalysts gave
absence of base led to a drop in yields (entries 3 and comparable yields for cis-cyclic 1,2-diol substrates. On
4). Other oxidants screened, including 1,3-dibromo- the other hand, for trans-cyclic 1,2-diols and acyclic
5,5-dimethyl-hydantoin (DBDMH), N-bromosuccin- diols with bulky alkyl chains, MeB(OH)2 and 3-
ACHTUNGTRENNUNGimide (NBS) and Br2, were not efficient in effecting methyl-2-buten-2-ylboronic acid catalysts gave superi-
this oxidation (entries 5–7). We next screened various or results (see the Supporting Information). The rela-
boronic acid catalysts to determine their suitability tively high cost of 3-methyl-2-buten-2-ylboronic acid
for selective oxidation in water. The results are sum- restricted much of this study to 4-MeOC6H4B(OH)2
marized in Table 2. Among the substituted phenylbor- and MeB(OH)2 catalysts. The results are summarized
onic acid catalysts screened, the MeO-substituted one in Table 3. All meso- and trans-cyclic 1,2-diols, under-
gave the best yields (entries 1–4). Phenylboronic acids went selective oxidation affording mono-oxidized
having Me-, F-, CN-, Br-, Cl- and CF3- substituents at products in good to excellent yields, with MeB(OH)2
ortho or para positions as well as unsubstitued as a catalyst of choice except for 1,2-diols 1a and 1d
PhB(OH)2 afforded good yields though lower than (entries 1–4) in which higher yields were obtained
Adv. Synth. Catal. 2014, 356, 934 – 940
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
935

COMMUNICATIONS
Julius M. William et al.
Table 3. Substrate scope of the 1,2-diols.
Entry
1,2-Diol
Temperature (Time)
Product
Yield [%][a]
1
2
3
08C (2 h)
08C (8 h)
08C (4 h)
b: n=3: 97, (98)[b]
c: n=2: 68
a, d: n=4: 81, (85)[b]
b, e: n=3: 94
4
5
08C (5 h)
08C (8 h)
c, f: n=2: 62
6
7
508C (7 h)
508C (7 h)
87
2g, 2h
89
94
8
9
r.t. (5 h)
r.t. (5 h)
96
10
11
12
13
08C (5 h)
r.t. (3 h)
08C (4 h)
r.t. (5 h)
r.t. (6 h)
91, (96)[c]
84, (85)[c]
88
80
86
14
[a]
Isolated yield.
4-MeOC6H4B(OH)2 was used.
3-Methyl-2-buten-2-ylboronic acid was used.
[b]
[c]
with 4-MeOC6H4B(OH)2 catalyst. Acyclic 1,2-diols obtain the corresponding a-hydroxy ketones in excel-
were also tolerated with substrates 1g and 1h being lent yields (entries 6 and 7). 1,2-Diol 1i underwent ox-
oxidized at an elevated temperature of 508C[25] to idation non-selectively at room temperature to give
936
asc.wiley-vch.de
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 934 – 940

COMMUNICATIONS
Boronic Acid-Catalyzed Selective Oxidation of 1,2-Diols
Table 4. Optimization of the electrochemical oxidation of
1a.
Scheme 2. Oxidation of boronate esters in water.
almost an equal mixture of a-hydroxy ketones 2ia and
2ib (entry 8). On the other hand, meso 1j smoothly
underwent selective oxidation affording 2j in excel-
lent yield (entry 9). Next, we carried out the selective
oxidation of 1,2-diols having both primary and secon-
dary alcohol functions. When 1,2-diols 1k, 1l, 1m, and
1n were treated under these catalytic conditions, the
secondary alcohols were selectively oxidized affording
products 2k, 2l, 2m, and 2n, respectively, in high
yields (entries 10–13). Additionally, 1,2,6-hexanetriol
1o underwent selective oxidation at the secondary hy-
droxy group of the 1,2-diol moiety affording 2o in sat-
isfactory yield (entry 14).
Entry
Optimization study
Yield [%][a]
1
2
3
4
5
0.02 equiv. of MeB(OH)2
0.02 equiv. of 4-MeOC6H4B(OH)2
0.01 equiv. of MeB(OH)2
0.25 equiv. of KBr
98
81
94
61
86
NaBr instead of KBr
[a]
Isolated yield.
Narasaka and Sharpless designed a process for the platinum electrodes. The results are summarized in
dihydroxylation of olefins by use of phenylboronic Table 4. After optimization, we found that KBr
acid as a diol captor leading to the formation of phe- (0.5 equiv.) and MeB(OH)2 (0.02 equiv.) afforded an
nylboronate ester.[26,27,28] This method has proved excellent yield of 98% (entry 1). Using 4-
useful for the synthesis of water-soluble diols. In MeOC6H4B(OH)2 instead of MeB(OH)2 lead to
order to get some insight on whether a boronate ester a drop in yield (entry 2). Lowering the amount of
plays the role of the intermediate in our reaction, we MeB(OH)2 to 0.01 equiv, as well as the amount of
syntheized boronate ester 3 using the Narasaka proce- KBr to 0.25 equiv, also led to drops in yields (entries 4
dure,[27] and subjected it to our oxidation conditions and 5). With the optimum conditions in hand, sub-
in water. The reaction gave a 47% yield of a-hydroxy strate applicability was next explored. The results are
ketone 2a and was accompanied by the hydrolysis of summarized in Table 5. All meso- and trans-cyclic 1,2-
the boronate ester to the corresponding cis-1,2-cyclo- diols, underwent selective oxidation affording mono-
octanediol 1a (Scheme 2).
oxidized products in moderate to excellent yields (en-
This reaction, although not unequivocally, hints tries 1–5). Acyclic 1,2-diol 1i underwent selective oxi-
that the boronate ester intermediate is involved in dation at room temperature to give a mixture of a-hy-
our reaction.
droxy ketones 2ia and 2ib in good yield (entry 6).
Acyclic 1,2-diol 1j was converted to the desired
With the success of chemical oxidation using boron-
ic acid catalysts, we envisaged that we can make the product 2j in excellent yield at room temperature
process cleaner by developing an electrochemical oxi- (entry 7). Next, we carried out selective oxidation of
dation process. Electrochemical oxidation avoids the 1,2-diols having both primary and secondary alcohol
use of chemical oxidants and the need for bases, some functions. When 1,2-diols 1k, 1l, 1m, and 1n were
of which are toxic to people and the environment. treated under these catalytic conditions, the secondary
Our earlier reported method on the electrochemical alcohols were selectively oxidized preferentially to
oxidation of 1,2-diols in water catalyzed by give products 2k, 2l, 2m, and 2n, respectively, in good
[15]
Me2SnCl2 faces drawbacks such as low yields and yield (entries 8–11). Additionally, 1,2,6-hexanetriol 1o
requires large amounts of electrolyte for some sub- underwent selective oxidation at the secondary hy-
strates. The key to a chemical oxidation reaction is droxy group of the 1,2-diol moiety affording 2o in
the activation of 1,2-diols with boronic acid leading to good yield (entry 12). In this electrochemical oxida-
the formation of a boronate intermediate. This is fol- tion, the 1,2-diol is activated by the boronic acid cata-
lowed by oxidation of the boronate intermediate with lyst to generate a boronate ester intermediate. The
DBI as a terminal oxidant. Therefore, we realized “Br+” ion, generated at the anode, plays the oxidant
that if the boronate was exposed to electrochemical role. The OHÀ ion electro-generated at the cathode
oxidation conditions, selective oxidation would be plays the role of the base.[15] A proposed reaction
achieved. We began this investigation with KBr as pathway for selective oxidation of 1,2-diol 1 in water
a bromide ion source, MeB(OH)2 as the catalyst and is shown in Scheme 3. Boronate ester A or nucleo-
cis-cyclooctan-1,2-diol 1a as a model substrate using phile A’ (activated intermediates), could be oxidized
Adv. Synth. Catal. 2014, 356, 934 – 940
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
937

COMMUNICATIONS
Julius M. William et al.
Table 5. Electrochemical oxidation of various 1,2-diols mediated by MeB(OH)2.
Entry
1
1,2-Diol
Product
Yield [%][a]
98
a: n=4
2
3
b: n=3
c: n=2
97
61
4
5
a, d: n=4
b, e: n=3
81
93
6[c]
67[b]
7[c]
90[b]
8[c]
9[d]
70
80[b]
10[c]
11[d]
68[b]
77[b]
71
12
[a]
Isolated yield.
Reaction done at room temperature.
1.0 equiv. of KBr was used.
[b]
[c]
[d]
Mixture of 0.5 equiv. of MgBr2 and 0.5 equiv. of Et4NBr was used.
by Br+ generated from the terminal oxidant or elec- excellent yields. This oxidation provides an efficient
trochemically generated in water leading to 2. and an environmentally friendly process, except for
In conclusion, we have successfully designed high a few challenges like low solubility of some substrates
yielding and safer chemical and electrochemical meth- in water, which required the reaction to be conducted
ods for the oxidation of 1,2-diols in water using a bor- at elevated temperature. We are currently studying
onic acid catalyst to activate the 1,2-diol moieties. this mode of activation in oxidation of sugars and the
Various cyclic and acyclic 1,2-diols have been selec- possibility of achieving enantioselective oxidation
tively oxidized to afford a-hydroxy ketones in good to with water-soluble boronic acid catalysts.
938
asc.wiley-vch.de
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 934 – 940

COMMUNICATIONS
Boronic Acid-Catalyzed Selective Oxidation of 1,2-Diols
(C) from the Japan Society for the Promotion of Science, Re-
search Grant for Pharmaceutical Sciences from Takeda Sci-
ence Foundation, and the Presidentꢀs Discretion Fund of Na-
gasaki University.
References
[1] a) P. T. Anastas J. C. Warner, Green Chemistry, Theory
and Practice, Oxford University Press, Oxford, 1998;
b) M. Eissen, J. O. Metzger, E. Schmidt, U. Schneide-
wind, Angew. Chem. 2002, 114, 402–425; Angew. Chem.
Int. Ed. 2002, 41, 414–436.
[2] Recent reviews: a) R. Noyori, M. Aoki, K. Sato, Chem.
Commun. 2003, 1977–1986; b) R. Irie, T. Katsuki,
Chem. Rec. 2004, 4, 96–109; c) T. Mallat, A. Baiker,
Chem. Rev. 2004, 104, 3037–3058; d) M. J. Schultz,
M. S. Sigman, Tetrahedron 2006, 62, 8227–8241.
[3] V. Kumar, W. A. Remers, W. T. Bradner, J. Med. Chem.
1980, 23, 376–384.
Scheme 3. Proposed reaction pathway for selective oxidation
in water.
Experimental Section
[4] R. Uchida, K. Shiomi, J. Inokoshi, R. Masuma, T. Ka-
wakubo, H. Tanaka, Y. Iwai, S. Omura, J. Antibiot.
1996, 49, 932–934.
[5] a) L. D. Accolti, A. Detomaso, C. Fusco, A. Rosa, R.
Curci, J. Org. Chem. 1993, 58, 3600–3601; b) W. Adam,
C. R. Shaha-Mcller, C. G. Zhao, J. Org. Chem. 1999, 64,
7492–7497; c) B. Plietker, Org. Lett. 2004, 6, 289–291.
[6] W. A. Cramp, F. J. Julietti, J. F. McGhie, B. L. Rao,
W. A. Ross, J. Chem. Soc. 1960, 4257–4263.
General Procedure for Chemical Oxidation of 1,2-
Diols in Water using DBI as an Oxidant
DBI (1.0 mmol) was added to a solution of 1,2-diol 1a
(1.0 mmol), methylboronic acid (0.1 mmol), and K2CO3
(1.2 mmol) in water (4 mL) at 08C under shielding from
light conditions. After the reaction mixture had been stirred
for 1 h, aqueous saturated Na2S2O3 solution (10 mL) was
added. The organic portion was extracted with AcOEt (3ꢁ
40 mL) and then dried over MgSO4. The solvent was re-
moved under vacuum and the residue was subjected to silica
gel column chromatography (n-hexane/AcOEt 5:1) to afford
product 2a; yield: 141 mg (99%).
[7] M. Ftizon, M. Golfier, J. M. Louis, J. Chem. Soc. (D)
1969, 1102–1102.
[8] E. J. Corey, C. U. Kim, Tetrahedron Lett. 1974, 15, 287–
290.
[9] Y. Sakata, Y. Ishii, J. Org. Chem. 1991, 56, 6233–6235.
[10] a) L. F. Walker, A. Bourghida, S. Connolly, M. Wills, J.
General Procedure for Electrochemical Oxidation of
1,2-Diols
Chem. Soc. Perkin Trans.
1 2002, 965–981; b) T.
Yamato, T. Hironaka, T. Saisyo, T. Manabe, K. Okuya-
ma, J. Chem. Res. Synop. 2003, 63–65.
A solution of 1,2-diol 1a (1.0 mmol) and methylboronic acid
(0.02 mmol) in water (4 mL) was stirred at room tempera-
ture for 10 min before electrolysis. The resulting solution
was transferred into a glass cell equipped with a platinum
anode and cathode (1ꢁ2 cm). KBr (0.5 mmol) was added to
the solution as an electrolyte. Then, the mixture was subject-
ed to constant current electrolysis (10 mA) at 08C shielded
from light (dark conditions) until 1a had disappeared, as
monitored by TLC. After completion of the reaction, aque-
ous saturated Na2S2O3 solçution (10 mL) was added. The or-
ganic portion was extracted with AcOEt (3ꢁ40 mL) and
then dried over MgSO4. The solvent was removed under
vacuum and the residue was subjected to silica gel column
chromatography (n-hexane/AcOEt=5:1) to afford product
2a; yield: 139.8 mg (98%).
[11] a) T. Maki, S. Iikawa, G. Mogami, H. Harasawa, Y.
Matsumura, O. Onomura, Chem. Eur. J. 2009, 15,
5364–5370; b) O. Onomura, H. Arimoto, Y. Matsu-
mura, Y. Demizu, Tetrahedron Lett. 2007, 48, 8668–
8672.
[12] T. Maki, K. Fukae, H. Harasawa, T. Ohishi, Y. Matsu-
mura, O. Onomura, Tetrahedron Lett. 1998, 39, 651–
654.
[13] C.-J. Li, L. Chen, Chem. Soc. Rev. 2006, 35, 68–82.
[14] J. M. William, M. Kuriyama, O. Onomura, RSC Adv.
2013, 3, 19247–19250.
[15] J. M. William, M. Kuriyama, O. Onomura, Electro-
chemistry 2013, 81, 374–376.
[16] For the benzoylation of 1,2-diols catalyzed by organotin
compounds, see: a) F. Iwasaki, T. Maki, W. Nakashima,
O. Onomura, Y. Matsumura, Org. Lett. 1999, 1, 969–
972; b) F. Iwasaki, T. Maki, W. Nakashima, O. Ono-
mura, Y. Matsumura, J. Org. Chem. 2000, 65, 996–1002;
c) W. Muramatsu, J. M. William, O. Onomura, J. Org.
Chem. 2012, 77, 754–759; d) Y. Demizu, Y. Kubo, H.
Miyoshi, T. Maki, Y. Matsumura, N. Moriyama, O.
Onomura, Org. Lett. 2008, 10, 5075–5077.
Acknowledgements
This research was supported by MEXT KAKENHI Grant
Number 23105539 as Grant-in-Aid for Scientific Research on
Innovative Areas from the Ministry of Education, Culture,
Sports, Science and Technology, JSPS KAKENHI Grant
Number 24590012 as Grant-in-Aid for Scientific Research
[17] For safety and toxicity of organotin catalysts see: a) C.
Rey, H. J. Reinecke, R. Besser, Vet. Hum. Toxicol.
Adv. Synth. Catal. 2014, 356, 934 – 940
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
939

COMMUNICATIONS
Julius M. William et al.
1984, 26, 121–122; b) T. Hamasaki, T. Sato, H. Nagase,
H. Kito, Mutat. Res. 1992, 280, 195–203; c) T. Hamasa-
ki, T. Sato, H. Nagase, H. Kito, Mutat. Res. 1993, 300,
265–271; d) M. Ema, R. Kurosaka, H. Amano, Y.
Ogawa, J. Appl. Toxicol. 1995, 15, 297–302; e) M. M.
Whalen, B. G. Loganathan, K. Kannan, Environmental
Res. 1999, 81, 108–116.
Sandanayake, S. Shinkai, Angew. Chem. 1996, 108,
2038–2050; Angew. Chem. Int. Ed. Engl. 1996, 35,
1910–1922; d) W. Wang, S. Gao, B. Wang, Org. Lett.
1999, 1, 1209–1212.
[23] T. Maki, N. Ushijima, Y. Matsumura, O. Onomura, Tet-
rahedron Lett. 2009, 50, 1466–1468.
[24] W. Gottardi, Monatsh. Chem. 1968, 99, 815–822.
[25] Performing the reaction at elevated temperatures im-
proved the solubility of substrates which have poor sol-
ubility in water.
[18] A. Suzuki, J. Organomet. Chem. 1999, 576, 147–168.
[19] R. Franzen, Can. J. Chem. 2000, 78, 957–962.
[20] R. Franzen, Y. Xu, Can. J. Chem. 2005, 83, 266–272.
[21] G. Springsteen, B. Wang, Tetrahedron 2002, 58, 5291–
5300.
[26] H. Sakurai, N. Iwasawa, K. Narasaka, Bull. Chem. Soc.
Jpn. 1996, 69, 2585–2594.
[22] a) T. D. James, K. R. A. S. Sandanayake, R. Iguchi, S.
Shinkai, J. Am. Chem. Soc. 1995, 117, 8982–8987; b) H.
Eggert, J. Frederiksen, C. Morin, J. C. Norrild, J. Org.
Chem. 1999, 64, 3846–3852; c) T. D. James, K. R. A. S.
[27] N. Iwasawa, T. Kato, K. Narasaka, Chem. Lett. 1988,
1721–1724.
[28] A. Gypser, D. Michel, D. S. Nirschl, K. B. Sharpless, J.
Org. Chem. 1998, 63, 7322–7327.
940
asc.wiley-vch.de
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 934 – 940