A practical RuCl3-catalyzed oxidation using trichlproisocyanuric acid as a stoichiometric oxidant under mild nonacidic conditions

Article abstract of DOI:10.1021/op049940k

The combined use of catalytic RuCl₃ (1.0 mol %) and stoichiometric trichloroisocyanuric acid (TCCA; 1.0 equiv) in the presence of n-Bu₄NBr (2.0 mol %) and K₂CO₃ (3.0 equiv) in 1:1 MeCN/H₂O at 25-45°C allows smooth oxidation of primary alcohols to carboxylic acids. Secondary alcohols can be oxidized to ketones when using the same set of the reagents in 1:1 MeCN/ H₂O or 1:1 AcOEt/H₂O. By proceeding under the nonacidic biphasic conditions dispensing with hazardous reagents, the oxidation reactions are applicable to structurally diverse alcohols, easy to work up, environmentally benign, and basically high-yielding.

Full text of DOI:10.1021/op049940k

Organic Process Research & Development 2004, 8, 931−938
A Practical RuCl -Catalyzed Oxidation Using Trichloroisocyanuric Acid As a
3
Stoichiometric Oxidant under Mild Nonacidic Conditions
†
†
,‡
Hidenori Yamaoka, Narimasa Moriya, and Masaya Ikunaka*
The Second Laboratories, Research and DeVelopment Center, Nagase & Co., Ltd.,
2
-2-3 Murotani, Nishi-ku, Kobe, 651-2241, Hyogo, Japan, and Product DeVelopment Section 4,
Bio/Fine Chemicals DiVision, Nagase ChemteX Corporation, 2-2-3 Murotani,
Nishi-ku, Kobe, Hyogo, 651-2241, Japan
Abstract:
Scheme 1. Oxidation of alcohols to carboxylic acids or
ketones
3
The combined use of catalytic RuCl (1.0 mol %) and stoichio-
metric trichloroisocyanuric acid (TCCA; 1.0 equiv) in the
presence of n-Bu NBr (2.0 mol %) and K CO (3.0 equiv) in
:1 MeCN/H O at 25-45 °C allows smooth oxidation of primary
4
2
3
1
2
alcohols to carboxylic acids. Secondary alcohols can be oxidized
to ketones when using the same set of the reagents in 1:1 MeCN/
H O or 1:1 AcOEt/H O. By proceeding under the nonacidic
2 2
biphasic conditions dispensing with hazardous reagents, the
oxidation reactions are applicable to structurally diverse alco-
hols, easy to work up, environmentally benign, and basically
high-yielding.
4
aldehydes 2 and NaClO
aldehydes 2 to carboxylic acids 3, while tandem one-pot
procedures have also been developed wherein NaClO is used
concomitantly with NaClO in the presence of catalytic
2
-mediated oxidation of the resulting
Introduction
5
With the adjustment of a molecular oxidation state playing
a vital role in both total synthesis of natural products and
industrial production of organic compounds, intensive effort
has been directed towards developing preparative methods
to oxidize alcohol groups in multifunctional compounds to
1
2
2
,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO).6 Indeed,
,7
2
such one-pot procedures are mild enough to find some
applications; however, it is the same nature of mildness that
has detracted from their practicality as they require a long
reaction time when applied to the oxidation of primary
carbonyl or carboxylic groups without affecting the other
existent functionalities.3
Despite a quantum leap in recent synthetic methodologies,
oxidation of primary alcohols 1 to carboxylic acids 3 still
lacks definitive options, whereas there are different effective
6
b
alcohols with a relatively complex structure.
8
When using Jones’ reagent, a range of primary alcohols
could be oxidized to carboxylic acids 3 in a more
expeditious manner (Scheme 1), and it is the reason that no
reagent has been more commonly used than Jones’ reagent
in the laboratory since its advent in 1946 despite the fact
1
tools to oxidize primary alcohols 1 to aldehydes 2 (Scheme
4
1
). Thus, the prevailing method to oxidize primary alcohols
1
to carboxylic acids 3 often depends on discrete two-step
8
procedures involving oxidation of primary 1 alcohols 1 to
that this classical method has suffered from two drawbacks:
(
1) too acidic conditions such that acid-labile functionalities
*
To whom correspondence should be addressed. Telephone: +81 78 992
3
164. Fax: +81 78 992 1050. E-mail: masaya.ikunaka@nagase.co.jp.
†
Nagase ChemteX Corporation.
Nagase & Co., Ltd.
(4) (a) Corey, E. J.; Suggs, J. W. Tetrahedron Lett. 1975, 2647. (b) Corey, E.
J.; Schmidt, G. Tetrahedron Lett. 1979, 399. (c) Dess, D. B.; Martin, J. C.
J. Org. Chem. 1983, 48, 4155. (d) Ley, S. V.; Norman, J.; Griffith, W. P.;
Marsden, S. P. Synthesis 1994, 639. (e) Mancuso, A. J.; Huang, S.-L.; Swern,
D. J. Org. Chem. 1978, 43, 2480. (f) Parikh, J. R.; Doering, W. E. J. Am.
Chem. Soc. 1967, 89, 5505. (g) Anelli, P. L.: Montanari, F.; Quichi, S.
Org. Synth. 1990, 69, 212. (h) de Nooy, A. E. J.; Besemer, A. C.; van
Bekkum, H. Synthesis 1996, 1153. (i) Einhorn, J.; Einhorn, C.; Ratajczak,
F.; Pierre, J.-L. J. Org. Chem. 1996, 61, 7452.
(5) (a) Dalancale, E.; Montanari, F. J. Org. Chem. 1986, 51, 567. (b) Wovkulich,
P. M.; Shankaran, K.; Kiegiel, J.; Uskokovi c´ , M. R. J. Org. Chem. 1993,
58, 832.
(6) (a) Zhao, M.; Li., J.; Mano, E.; Song, Z.; Tschaen, D. M.; Grabowski, E.
J. J.; Reider, P. J. J. Org. Chem. 1999, 64, 2564. (b) Ikunaka, M.;
Matsumoto, J.; Nishimoto, Y. Tetrahedron: Asymmetry 2002, 13, 1201.
(7) Zanka, A. Chem. Pharm. Bull. 2003, 51, 888.
‡
(
1) Nicholaou, K. C.; Snyder, S. A. Classics in Total Synthesis II: More Targets,
Strategies, Methods; Wiley-VCH: Weinheim, 2003. (b) Nicholaou, K. C.;
Sorensen, E. J. Classics in Total Synthesis: Targets, Strategies, Methods;
VCH: Weinheim, 1996. (c) Total Synthesis of Natural Products: Today,
Tomorrow and Beyond; Tatsuta, K., Kitahara, T., Fukuyama, T., Ed.; Kikan
Kagaku Sosetsu, No. 45; Japan Scientific Societies Press: Tokyo, 2000.
2) (a) Anderson, N. G. Practical Process Research & DeVelopment; Academic
Press: San Diego, 2000. (b) Chemical Process Research: The Art of
Practical Organic Synthesis; Abdel-Magid, A. F., Ragan, J. A., Ed.; ACS
Symposium Series 870; America Chemical Society: Washington, DC, 2004.
3) (a) Hudlicky, M. Oxidation in Organic Chemistry; ACS Monograph 186,
America Chemical Society: Washington, DC, 1990. (b) Larock, R. C.
ComprehensiVe Organic Transformations: A Guide to Functional Group
Preparations, 2nd ed.; Wiley-VCH: New York, 1999; pp 1234-1255 for
oxidation of primary and secondary alcohols to the respective aldehydes
and ketones; pp 1646-1648 for oxidation of primary alcohols to carboxylic
acids.
(
(
(8) (a) Bowden, K.; Heilbron, I. M.; Jones, E. R. H.; Weedon, B. C. L. J. Chem.
Soc. 1946, 39. (b) Bowers, A.; Halsall, T. G.; Jones, E. R. H.; Lemin, A.
J. J. Chem. Soc. 1953, 2548.
1
0.1021/op049940k CCC: $27.50 © 2004 American Chemical Society
Vol. 8, No. 6, 2004 / Organic Process Research & Development
•
931
Published on Web 10/08/2004

cannot survive and (2) use of environmentally demanding
toxic chromium(VI) species.
Corey’s pyridinium dichromate (PDC) in DMF4b could
have been used more frequently to oxidize primary alcohols
3
Scheme 2. RuCl /TCCA-mediated oxidation in the
presence of TBAB as a phase transfer catalyst
1
to carboxylic acids 3 because of the neutral nature of the
reaction (Scheme 1). However, besides the hazardous nature
of the chromium species in PDC, use of the polar solvent of
DMF has kept the PDC-mediated oxidation from being
practical due to the difficulty in separating the carboxylic
9
acid products 3 from DMF through the extractive workup.
To effect the oxidation of primary alcohols 1 to carboxylic
acids 3 in a more environmentally benign manner, Noyori’s
chromium-free conditions could be applied where aqueous
H O
2 2
is used as a stoichiometric oxidant in combination with
a catalytic amount of Na WO in the presence of [Me(n-
N]HSO as a phase transfer catalyst (Scheme 1).
However, this oxidation protocol has found limited use so
far because of the severely acidic nature of the reaction
media;10b thus, the situation seems not to have changed so
much from that about half a century ago with respect to
2
4
1
0
C
8 17
H )
3
4
on the literature precedents for a new and improved
combination of the relevant reagents that would meet the
following requirements: (1) wide applicability owing to
sufficient power of oxidation; (2) mild nonacidic milieu in
which a range of functionalities can survive unaffected; (3)
environmentally benign conditions dispensing with chromium
species and halogenated solvents; and (4) facile product
isolation due to no use of polar aprotic solvents, such as
DMF and DMSO. Experimental effort along these lines has
eventually culminated in identification of a practical recipe
for the alcohol oxidation that features the combined use of
practicality, still suffering a tradeoff between applicability
and environmental friendliness.11
When it comes to oxidation of secondary alcohols 4 to
ketones 5, the standard methods to oxidize primary alcohols
4
1
to aldehydes 2 are also applicable (Scheme 1). In addition,
Albright and Goldman’s method using Ac
2
O and DMSO is
also effective for the oxidation of sterically hindered second-
1
2
3
catalytic RuCl and stoichiometric trichloroisocyanuric acid
ary alcohols 5. In fact, being so mild and chemoselective,
2 3
(TCCA) in the presence of K CO as an acid scavenger under
oxidation using activated DMSO has now won renown as a
4e,4f
the phase transfer conditions catalyzed by n-Bu NBr (Scheme
versatile preparative method, whether the desired products
are aldehydes or ketones.13 However, use of excess DMSO
sometimes poses practical problems, such as stench and
troublesome product isolation. In particular, the issue of
product isolation (separation of polar products from the
DMSO used without recourse to silica gel chromatography)
can make the DMSO-mediated oxidation less amenable to
scale-up when it is applied to the oxidation of polar
4
2).
Results and Discussion
In the course of extensive experimentation designed to
address the above-defined issues, RuCl
3
-catalyzed oxidation15
turned out promising, while the standard Sharpless protocol
has remained less than satisfactory, since it employs expen-
substrates, such as sugar derivatives.1
4
4 4
sive NaIO as a stoichiometric oxidant and toxic CCl as an
15a
essential component of the reaction medium. Interestingly,
RuCl proved to work as an effective oxidation catalyst in a
heterogeneous system (1:1 MeCN/H O) when it was used
in combination with stoichiometric trichloroisocyanuric acid
To overcome the above-discussed limitations of the
present methodologies to oxidize primary and secondary
alcohols 1 and 4 to carboxylic acids 3 and ketones 5,
respectively, sets of reaction variables were explored based
3
2
1
6
(
TCCA; 1.0 equiv), an inexpensive oxidant miscible freely
with organic solvents of low polarity. Further investigation
showed that addition of n-Bu NBr (TBAB; 2.0 mol %) as a
allowed the usage of RuCl to be
reduced to no more than 1.0 mol %; and what was better,
the progress of the RuCl /TCCA/TBAB-mediated oxidation
(
9) The workup procedures recommended in ref 4b for the PDC-mediated
oxidation of primary alcohols to carboxylic acids in DMF involve pouring
the reaction mixture into water followed by extraction with ether or ether/
pentane; however, few carboxylic acids of high polarity would be extracted
into such solvent(s).
4
4
i,17
phase transfer catalyst
3
(
10) (a) Sato, K.; Aoki, M.; Takagi, J.; Noyori, R. J. Am. Chem. Soc. 1997, 119,
2386. (b) Sato, K.; Aoki, M.; Takagi, J.; Zimmermann, K.; Noyori, R.
3
1
Bull. Chem. Soc. Jpn. 1999, 72, 2287. (c) Sato, K. Yuki Gosei Kagaku
Kyokaishi 2002, 60, 974.
11) For the catalytic version of chromium trioxide-mediated oxidation of primary
alcohols to carboxylic acids using periodic acid as a stoichiometric oxidant,
see: Zhao, M.; Li, J.; Song, Z.; Desmond, R.; Tschaen, D. M.; Grabowski,
E. J. J.; Reider, P. J. Tetrahedron Lett. 1998, 39, 5323.
(15) (a) Carlsen, P. H. J.; Katsuki, T.; Martin, V. S.; Sharpless, K. B. J. Org.
Chem. 1981, 46, 3936. (b) Fleitz, F. J.; Lyle, T. A.; Zheng, N.; Armstrong,
J. D., III.; Volante, R. P. Synth. Commun. 2000, 30, 3171.
(16) (a) For a comprehensive review on the use of TCCA as an oxidant, see:
Tilstman, U.; Weinmann, H. Org. Process Res. DeV. 2002, 6, 384. (b) For
the TEMPO (2.0 mol %)-catalyzed oxidation of alcohols to carboxylic acids
using TCCA (2.0 equiv) as a stoichiometric oxidant in acetone in the
(
(
(
12) Albright, J. D.; Goldman, L. J. Am. Chem. Soc. 1965, 87, 4214.
13) (a) Zanka, A.; Itoh, N.; Kuroda, S. Org. Process Res. DeV. 1999, 3, 394.
(b) Wang, C.-C.; Li, J. J.; Huang, H.-C.; Lee, L. F.; Reitz, D. B. J. Org.
3
presence of catalytic NaBr (0.2 equiv) and an aqueous NaHCO solution,
Chem. 2000, 65, 2711.(c) Yamada, S.; Mori, Y.; Morimatsu, K.; Ishizu,
Y.; Ozaki, Y.; Yoshioka, R.; Nakatani, T.; Seko, H. J. Org. Chem. 1996,
see: Luca, L. D.; Giacomelli, G.; Masala, S.; Porcheddu, A. J. Org. Chem.
2003, 68, 4999.
6
1, 8586.
3 2 2 2 2
(17) For the RuCl -catalyzed oxidation with H O in a biphasic Cl(CH ) Cl/
(
14) (a) Sowa, W.; Thomas, G. H. S. Can. J. Chem. 1966, 44, 836. (b)
Brimacombe, J. S.; Bryan, J. G. H.; Husain, A.; Stacey, M.; Tolley, M. S.
Carbohydr. Res. 1967, 3, 318.
H
2
O system using didecyldimethylammonium bromide as a phase transfer
catalyst, see: Barak, G.; Dakka, J.; Sasson, Y. J. Org. Chem. 1988, 53,
3553.
932
•
Vol. 8, No. 6, 2004 / Organic Process Research & Development

Scheme 3. Stoichiometry for the RuCl
oxidation
3
/TCCA-mediated
3
Table 1. RuCl /TCCA-Mediated oxidation of 1-octanol 1a to
octanoic acid 3a in the presence of a range of bases
a
product composition (%) after 3.0 hb
entry
base
octanol 1a octanal 2a octanoic acid 3a
1
2
3
4
5
6
NaOH
0
0
0
0
89.5
0
0
0
0
8.2
0
80.6
98.4
85.9
75.6
0
K
2
CO
NaHCO
pyridine
Et
none
3
3
3
N
9.9
69.3
a
A 1.0 M MeCN solution of TCCA (1.0 equiv) was added dropwise to a
2 3
stirred mixture of 1a (0.5 M) and 1:1 MeCN/H O in the presence of RuCl (1.0
mol %), TBAB (2.0 mol %), and a specified base (3.0 equiv) at 25-45 °C, and
b
the mixture was stirred at the same temperature range for 3 h. Determined by
GLC using n-tridecane as an internal standard after the generated 3a was
23
3 2
converted to the corresponding methyl ester with Me SiCHN ; for the detailed
conditions, see procedure 1 in Experimental Section.
Table 2. Effects of pH on the RuCl
3
/TCCA-mediated
oxidation of 1-octanol 1a to octanoic acid 3aa
product composition (%) after 3.0 hb
octanol 1a octanal 2a octanoic acid 3a
entry
pH
1
2
3
5
7
9
0
0
0
0
0
0
82.5
83.3
100
turned out to be less affected by the presence of an acid
scavenger such as K CO (3.0 equiv), as discussed in detail
2 3
below, which should help the oxidation to proceed under
mild nonacidic conditions (Scheme 2).19
Oxidation of Primary Alcohols. TCCA 6 is converted
into cyanuric acid (CNA) 7 with generation of HCl when
18
a
A 1.0 M MeCN solution of TCCA (1.0 equiv) was added dropwise to a
stirred mixture of 1a (0.5 M) and 1:1 MeCN/1.0 M potassium phosphate buffer
adjusted to a specified pH value in the presence of RuCl (1.0 mol %) and TBAB
3
(
2.0 mol %) at 25-45 °C, and the mixture was stirred at the same temperature
range for 3 h during which the pH of the mixture was maintained at an indicated
b
value by adding a 3.0 M aqueous K
2 3
CO solution. Determined by GLC using
n-tridecane as an internal standard after the generated 3a was converted to the
working as the stoichiometric oxidant for the RuCl
3
-catalyzed
23
corresponding methyl ester with Me
procedure 2 in Experimental Section.
3 2
SiCHN ; for the detailed conditions, see
oxidation of alcohols (Scheme 3). Thus, for the oxidation to
be compatible with acid-susceptible functionalities, the
released HCl and the generated CNA 7 should both be
neutralized with a pertinent base that would not affect the
oxidation itself. Thus, some common bases were tested for
the compatibility with the oxidation of 1-octanol 1a with
Table 3. Effects of organic solvent species on the RuCl
TCCA-mediated oxidation of 1-octanol 1a to octanoic acid
3
/
a
3
a
product composition (%) after 3.0 hb
RuCl
of TBAB (2.0 mol %) in 1:1 MeCN/H
the oxidation of 1-octanol 1a was attempted in the presence
of NaOH, NaHCO , or K CO each in 3.0 molar equivalents,
it went to completion in 3 h to give octanoic acid 3a in a
GLC yield of 80.6%, 98.4%, and 85.9%, respectively, against
an internal standard (n-tridecane) without intermediate oc-
tanal 2a being detected.
In contrast, the oxidation running in the presence of
pyridine (3.0 equiv) provided 3a (76%) and 2a (8%), the
product distribution being similar to that for the oxidation
in the absence of any base, 69.3:9.9 3a/2a. Moreover, when
3
(1.0 mol %) and TCCA (1.0 equiv) in the presence
octanol
octanal
octanoic
entry
organic solvent
MeCN
AcOEt
MeCOi-Pr (MIBK)
PhMe
1a
2a
acid 3a
2
O (Table 1): when
1
2
3
4
5
0
0
0
0
0
0
93.0
74.4
37.8
32.2
39.5
3
2
3
9.4
22.4
0
n-heptane
1.7
a
A 1.0 M solution of TCCA (1.0 equiv) in a specified organic solvent was
added dropwise to a stirred mixture of 1a (0.5 M) and 1:1 the organic solvent/
2 3 2 3
H O in the presence of RuCl (1.0 mol %), TBAB (2.0 mol %), and K CO (3.0
equiv) at 25-45 °C, and the mixture was stirred at the same temperature range
b
for 3 h. Determined by GLC using n-tridecane as an internal standard after the
23
3 2
generated 3a was converted to the corresponding methyl ester with Me SiCHN ;
for the detailed conditions, see procedure 1 in Experimental Section.
3
the oxidation was attempted in the presence of Et N (3.0
equiv), none of 3a was generated with 1a being left almost
unconsumed. While experimental evidence was lacking, it
3
was assumed that this phenomenon should result from Et N
diverting the RuCl
formation because Et
sity than pyridine.
3
/TCCA-mediated oxidation to its N-oxide
N has more electron-donating propen-
(
18) For the kinetics-oriented studies on the RuCl
3
/TCCA oxidation in acidic
media, see: (a) Pati, S. C.; Sahu, A. K.; Sriramulu, Y. Oxid. Commun.
3
1985/86, 8, 243. (b) Pati, S. C.; Pathy, H. P.; Dev, B. R. Oxid. Commun.
1987, 10, 19. (c) Pati, S. C.; Sahu, A. K.; Sriramulu, Y. Curr. Sci. 1988,
57, 325. (d) Pati, S. C.; Sahu, A. K.; Sriramulu, Y. ReV. Roum. Chim. 1988
33, 157. (e) Pati, S. C.; Sarangi, C. Ind. J. Chem. 1988, 27A, 593. (f) Pati,
Now that the highest GLC yield was recorded in the
presence of K CO (3.0 equiv), it was eventually nominated
2
3
S. C.; Patro, P. S. C. Proc. Indian Natl. Sci. Acad. 1989, 55A, 75. (e) Mohan,
R. V. G. K.; Sondu, S. React. Kinet. Catal. Lett. 1997, 61, 167.
as the most appropriate acid scavenger for the oxidation in
question.
(
19) Ikunaka, M.; Moriya, N.; Yamaoka, H. A patent application submitted.
Vol. 8, No. 6, 2004 / Organic Process Research & Development
•
933

Table 4. Best practices for the RuCl
3
/TCCA-mediated oxidation of primary alcohols to carboxylic acidsa
a
2
A 1.0 M MeCN solution of TCCA (1.0 equiv) was added dropwise to a stirred mixture of an alcohol substrate (0.5 M) and 1:1 MeCN/H O in the presence of
b
3 2 3
RuCl (1.0 mol %), TBAB (2.0 mol %), and K CO (3.0 equiv) at 25-45 °C, and the mixture was stirred at the same temperature range for 3 h. An isolated yield.
23
c
Determined by GLC using n-tridecane as an internal standard after the generated 3b was converted to the corresponding methyl ester with Me
3
SiCHN
2
;
for the
detailed conditions, see Experimental Section.
To define the pH range within which the oxidation would
proceed uneventfully, the oxidation of 1a was conducted at
pH 5, 7, or 9, each of which was kept constant by the
combined use of a 1.0 M potassium phosphate buffer and a
Table 5. Effects of pH on the RuCl /TCCA-mediated
3
oxidation of 2-octanol 4a to 2-octanone 5aa
product composition (%) after 3.0 hb
entry
pH
2-octanol 4a
2-octanone 5a
2 3
3.0 M aqueous K CO solution. As summarized in Table 2,
it was presumed that the oxidation at pH 9 provided the
highest GLC yield; however, the oxidation seems to proceed
smoothly at any pH value tested to give acid 3a selectively
when taking into account the experimental error associated
with the quantitative GLC analysis using an internal standard
and the complete consumption of the starting alcohol 1a in
each case.
The oxidation was next attempted in a range of organic
solvents to see what effect an organic solvent species would
have on the course of the oxidation (Table 3): a mixture of
1
2
3
5
7
9
0
0
0.8
100
98.4
78.2
a
A 1.0 M MeCN solution of TCCA (1.0 equiv) was added dropwise to a
stirred mixture of 4a (0.5 M) and 1:1 MeCN/1.0 M potassium phosphate buffer
3
adjusted to a specified pH value in the presence of RuCl (1.0 mol %) and TBAB
(
2.0 mol %) at 25-45 °C, and the mixture was stirred at the same temperature
range for 3 h during which the pH of the mixture was maintained at the indicated
b
2 3
value by adding a 3.0 M aqueous K CO solution. Determined by GLC using
n-tridecane as an internal standard; for the detailed conditions, see procedure 3
in Experimental Section.
1
-octanol 1a (0.5 M) and 1:1 organic solvent/H
2
O containing
CO (3.0
9 and at 25-45 °C for 3 h during which the specified pH
was maintained by adding a 3.0 M aqueous solution of
RuCl (1.0 mol %), TBAB (2.0 mol %), and K
3
2
3
equiv) was treated with a 1.0 M solution of TCCA (1.0 equiv)
in the organic solvent at 25-45 °C for 3.0 h, and the product
composition was analyzed by GLC quantitatively against an
internal standard (n-tridecane). When MeCN was used as
an organic phase, the GLC analysis indicated that octanoic
acid 3a was produced in 93.0% yield without any octanal
2 3
K CO . As summarized in Table 5, the oxidation proceeded
uneventfully under slightly acidic and neutral conditions as
2-octanone 5a was obtained quantitatively and in 98.4% yield
at pH 5 and 7, respectively, as indicated by quantitative GLC
analysis using n-tridecane as an internal standard. In contrast,
basic conditions proved detrimental to the oxidation of
secondary alcohols as GLC analysis showed that 5a was
generated in 78.2% yield at pH 9 with 4a being left
unconsumed in 0.8% yield.
2
a being detected. However, with decreasing polarity of the
organic solvents used, the GLC yield of 3a declined from
4.4% in AcOEt to 32.2% yield in PhMe with complete
7
consumption of 1a. In contrast, when the oxidation was
run in methyl isobutyl ketone (MIBK), its progress was
intercepted by the significant formation of aldehyde 2a
3
Interestingly, the RuCl /TCCA-mediated oxidation of
secondary alcohols to ketones would proceed better under
slightly basic conditions when compared with that of primary
alcohols to carboxylic acids. However, what is noticeable at
the moment is that the above-specified procedures have
enabled successful oxidation of secondary alcohols to ketones
under neutral conditions.
As regards the oxidation of secondary alcohols to ketones,
the best procedures for the oxidation of primary alcohols to
carboxylic acids also worked well: when a mixture of 4a
(
22.4%).
In light of the experimentation discussed above, the best
recipe to oxidize primary alcohols to carboxylic acids with
TCCA (1.0 equiv) by the catalysis of RuCl (1.0 mol %)
involves use of the biphasic MeCN/H O (1:1) mixture as a
reaction medium, TBAB (0.2 mol %) as a phase transfer
catalyst, and K CO (3.0 equiv) as an acid scavenger at 25-
5 °C. In fact, its reliable and versatile nature can be
confirmed by Table 4 listing a high isolated yield of 3a
94.9%) and a successful oxidation of acid-labile solketal
b to 2,2-dimethyl-1,3-dioxolane-4-carboxylic acid 3b (GLC
3
2
2
3
4
(0.5 M) and 1:1 MeCN/H
TBAB (2.0 mol %), and K
2
O containing RuCl
3
(1.0 mol %),
2
CO (3.0 equiv) was treated with
3
(
1
a 1.0 M solution of TCCA (1.0 equiv) at 25-45 °C, 4a was
consumed completely in 1 h to give 5a in an isolated yield
of 98.0%. When the oxidation of 4a was conducted in AcOEt
or MIBK otherwise under the same conditions as mentioned
above, 5a was produced almost quantitatively in 3 h as
indicated by quantitative GLC analysis using n-tridecane as
an internal standard. In contrast, however, use of n-heptane
yield of 96.0%).
Oxidation of Secondary Alcohols. As a test example,
2
-octanol 4a was treated with TCCA (1.0 equiv) in the
presence of RuCl (1.0 mol %) and TBAB (2.0 mol %) in
:1 MeCN/1.0 M potassium phosphate buffer at pH 5, 7, or
3
1
934
•
Vol. 8, No. 6, 2004 / Organic Process Research & Development

Table 6. RuCl
3
/TCCA-Mediated oxidation of diverse secondary alcohols to ketonesa
a
Unless otherwise specified, a 1.0 M MeCN solution of TCCA (1.0 equiv) was added dropwise to a stirred mixture of an alcohol substrate (0.5 M) and 1:1
MeCN/H O in the presence of RuCl (1.0 mol %), TBAB (2.0 mol %), and K CO (3.0 equiv) at 25-45 °C, and the mixture was stirred at the same temperature range
2
3
2
3
for 3 h. b Determined by GLC using n-tridecane as an internal standard; for the detailed conditions, see Experimental Section. A 0.67 M AcOEt solution of TCCA
c
d
(
0.67 equiv) was added to a stirred mixture of an alcohol substrate (0.5 M) and 1:1 AcOEt/H
detailed conditions, see Experimental Section. An isolated yield.
2
O. Determined by GLC using n-nonane as an internal standard; for the
e
Table 7. RuCl
3
/TCCA-Mediated benzyl alcohol 1c and cinnamyl alcohol 1da
a
Unless otherwise specified, a 1.0 M MeCN solution of TCCA (1.0 equiv) was added dropwise to a stirred mixture of an alcohol substrate (0.5 M) and 1:1
O in the presence of RuCl (1.0 mol %), TBAB (2.0 mol %), and K CO (3.0 equiv) at reflux, and the mixture was stirred at the same temperature range
MeCN/Hb
2
3
2
3
for 3 h. An isolated yield. c A 0.67 M AcOEt solution of TCCA (0.67 equiv) was added dropwise to a stirred mixture of an alcohol substrate (0.5 M) and 1:1
AcOEt/H
for 3 h.
2
O in the presence of RuCl
3
(1.0 mol %), TBAB (2.0 mol %), and K
2
CO
3
(3.0 equiv) at 25-45 °C, and the mixture was stirred at the same temperature range
as the organic phase required as long as 40 h until the
oxidation went to completion.
Oxidation of Unsaturated Alcohols. To complement the
scope and limitations studies on the RuCl /TCCA/TBAB-
3
To demonstrate its wide applicability and tunable nature
with respect to the organic phase and the acid scavenger, a
range of secondary alcohols were subjected to the RuCl /
3
mediated oxidation, benzyl alcohol 1c was subjected to the
oxidation conditions in question (Table 7). When using
MeCN as the organic phase, 1c was oxidized to benzoic acid
TCCA/TBAB-based oxidation method under somewhat
arbitrarily selected conditions as listed in Table 6. In fact,
successful oxidation of benzoin 4d, R-hydroxy ester (pan-
3
c in an isolated yield of 94%. In contrast, when AcOEt
was used as the organic phase, the oxidation gave only
benzaldehyde 2c in an isolated yield of 87%.
2
0
21
tolactone) 4e, and sugar derivatives 4f should highlight
the mild chemoselective nature of the oxidation thus
developed.
However, in the case of the oxidation of cinnamyl alcohol
1d, no such sharp selectivity was observed (Table 7). Indeed,
use of AcOEt as the organic phase allowed the selective
oxidation of 1d to cinnamaldehyde 2d in 98.5% yield.
However, when MeCN was used as the organic phase, the
(
(
20) Ojima, I.; Kogure, T.; Yoda, Y. Org. Synth. 1985, 63, 18.
21) Moore, B. S.; Cho, H.; Casati, R.; Kennedy, E.; Reynolds, K.; Mocek, U.;
Beale, J. M.; Floss, H. G. J. Am. Chem. Soc. 1993, 115, 5254.
Vol. 8, No. 6, 2004 / Organic Process Research & Development
•
935

oxidation ended up giving a mixture of 2d and cinnamic
acid 3d in an isolated yield of 63% and 36% yield,
respectively. Despite a paucity of experimental data, it was
presumed that unsaturated primary alcohols could be oxidized
selectively to aldehydes when AcOE was used as the organic
Procedures to Assess Effects of Organic Solvent
Species and Acid Scavengers on the Oxidation of 1-Oc-
tanol (1a) to Octanoic Acid (3a) by the Quantitative GLC
Analysis: Procedure 1. A solution of TCCA (700 mg, 3.01
mmol) in an organic solvent (3.00 mL; selected from Table
3) was added dropwise to a stirred mixture of 1-octanol 1a
3
phase for the RuCl /TCCA/TBAB-mediated oxidation.
(
472 µL, d 0.827, 3.00 mmol), a base (9.00 mmol; selected
from Table 1), RuCl (0.10 M aqueous solution; 0.30 mL,
0.0 µmol), TBAB (0.10 M aqueous solution; 0.60 mL, 60.0
Conclusions
3
As regards the newly developed biphasic oxidation
procedures [RuCl (1.0 mol %), TCCA (1.0 equiv), TBAB
2.0 mol %), K CO (3.0 equiv); 25-45 °C], comments
3
3
µmol), n-tridecane (365 µL, d 0.756, 1.50 mmol), and the
same organic solvent as that used to dissolve TCCA (3.00
mL) with water-cooling below 40 °C. The mixture was
stirred at 30 °C for 3 h. i-PrOH (2.0 mL) was added with
water-cooling below 40 °C, and the stirring was continued
at 30 °C for 30 min to destroy the unconsumed TCCA. A
(
2
3
worth making are itemized as follows: (1) Being essentially
neutral, the conditions are compatible with a range of
functional groups such as acid-labile acetals and base-labile
esters.22 (2) The pertinent organic phase being less polar
organic solvents, such as MeCN and AcOEt, the oxidation
product can be isolated in a facile practical manner. (3) The
conditions are free of environmentally hazardous toxic
reagents, such as chromium species and halogenated solvents
6
.0 M aqueous HCl solution was added at room temperature
until the pH of the mixture became 4.0. AcOEt (10.0 mL)
was added and the mixture was stirred at room temperature
for 10 min. From the organic phase of the mixture was taken
an aliquot (0.50 mL) to which was added MeOH (2 drops
from a Pasteur pipet). To the mixture was added a 10%
solution of Me SiCHN in n-hexane (purchased from Tokyo
3 2
Kasei) until the yellow color persisted. A 0.5 µL aliquot
including CH
carboxylic acids in 1:1 MeCN/H
can be oxidized smoothly to ketones in either 1:1 MeCN/
O or 1:1 AcOEt/H O. (6) Unsaturated primary alcohols,
such as benzyl alcohol 1c and cinnamyl alcohol 1d, can be
2
Cl
2
. (4) Primary alcohols are best oxidized to
2
O. (5) Secondary alcohols
H
2
2
of the mixture was injected to a gas chromatograph run-
2
oxidized selectively to aldehydes in 1:1 AcOEt/H O.
ning under condition 1: t
min for 2a, 6.2 min for methyl octanoate, and 7.9 min for
a.
Procedures to Assess Effects of pH on the Oxidation
R
4.4 min for n-tridecane, 5.1
Experimental Section
1
Melting points were measured on an Electrothermal
1
1
A8104 melting point apparatus and are uncorrected. H
13
NMR and C NMR spectra were recorded at 400 and 100
MHz, respectively, on a Varian UNITY-400 spectrometer
with tetramethylsilane as an internal standard in a solution
of 1-Octanol (1a) to Octanoic Acid (3a) by the Quantita-
tive GLC Analysis: Procedure 2. A solution of TCCA (700
mg, 3.01 mmol) in MeCN (3.00 mL) was added dropwise
to a stirred mixture of 1-octanol 1a (3.00 M solution in
of CDCl
60 FT-IR spectrometer. Mass spectra were recorded on a
3
. FT-IR spectra were recorded on a Nicolet Avatar
3
3
MeCN; 1.00 mL, 3.00 mmol), RuCl (0.10 M aqueous
Hitachi M-8000 mass spectrometer (ESI).
GLC Analysis. (1) Condition 1 to follow the oxidation
of 1-octanol 1a and 2-octanol 2a: column, Reoplex 400
solution; 0.30 mL, 30.0 µmol), TBAB (0.10 M aqueous
solution; 0.60 mL, 60.0 µmol), n-tridecane (365 µL, d 0.756,
1.50 mmol), and a 1.0 M potassium phosphate buffer (10.0
mL; pH 5, 7, or 9; Table 2) with water-cooling below 40
(
5
15% Chemosorb AWCS, 2 m × 3 mm φ); carrier gas, He,
0 mL/min; injection temperature, 250 °C; column temper-
2 3
°C. In the course of the addition, a 3.0 M aqueous K CO
ature, 120 °C (2 min) f 10 °C/min f 220 °C (8 min);
detection, FID at 250 °C; octanoic acid 3a was converted to
solution was added to maintain the same pH as set initially.
After the addition was completed, the mixture was stirred at
30 °C for 3 h. The reaction was worked up and analyzed
quantitatively according to procedure 1.
3
the corresponding methyl ester by treatment with Me -
23
SiCHN
2
prior to the analysis: for detail, vide infra. (2)
Condition 2 to follow the oxidation of solketal (2,2-dimethyl-
Octanoic Acid (3a). To a stirred mixture of 1-octanol
1,3-dioxolane-4-methanol) 1b, cyclopentanol 4b, benzhydrol
1a (390 mg, 2.99 mmol) and 1:1 MeCN/H O (6.0 mL) were
2
4
c: column, J & W Scientific DB-624 (30 m × 0.53 mm
added RuCl ‚3H O (7.80 mg, 30.0 µmol), TBAB (19.3 mg,
59.9 mmol), and K CO (1.24 g, 9.00 mmol) at room
2 3
3
2
φ); carrier gas, He, 27 cm/s; injection temperature, 260 °C;
column temperature, 130 °C (3 min) f 10 °C/min f 210
temperature. A solution of TCCA (700 mg, 3.01 mmol) in
MeCN (3.0 mL) was added dropwise during which the
reaction temperature was maintained at 25-45 °C with
water-cooling. The mixture was stirred at the same temper-
ature range for 1 h. i-PrOH (150 µL, 1.97 mmol) was added,
and the stirring was continued further for 1 h to destroy the
unconsumed TCCA. The mixture was filtered through a short
pad of Hyflo Super Cel to remove insoluble materials. To
the filtrate was added 5% aqueous HCl solution to adjust its
pH to 2.0. The layers were separated, and the aqueous layer
was extracted with AcOEt (1.5 mL × 1). The combined
organic layers were washed with saturated aqueous NaCl
°
C (4 min); detection, FID at 300 °C; 2,2-dimethyl-1,3-
dioxolane-4-carboxylic acid 3b was converted to the corre-
sponding methyl ester by treatment with Me
to the analysis: for detail, vide infra. To do the analysis
quantitatively under each condition, n-tridecane or n-nonane
was used as an internal standard depending on the retention
times shown by compounds being analyzed.
23
3
SiCHN
2
prior
(
22) While cinnamic alcohol 1d was oxidized to cinnamaldehyde 2d with its
double bond being unaffected, some preliminary experimentation indicated
that isolated double bonds were susceptible to the present oxidation
conditions.
(23) Hashimoto, N.; Aoyama, T.; Shioiri, T. Chem. Pharm. Bull. 1981, 29, 1475.
936
•
Vol. 8, No. 6, 2004 / Organic Process Research & Development

solution (2.0 mL × 2), dried (MgSO
vacuo to give 3a (410 mg) in 94.9% yield.
,2-Dimethyl-1,3-dioxolane-4-carboxylic Acid (3b).
Solketal 1b was subjected to the same conditions as described
for the oxidation of 1a to 3a. The reaction was worked up
and analyzed quantitatively according to procedure 1 except
that the GLC analysis was conducted under condition
4
), and concentrated in
AcOEt layers were washed with saturated aqueous NaCl
), and concentrated in
solution (10 mL × 2), dried (MgSO
4
2
vacuo to give 5d (3.27 g) in 77.7% yield: HPLC [column,
YMC-Pack ODS AM-3024 (6 mm φ × 150 mm); elution,
2
MeCN/H O (60:40), 1.0 mL/min; detection, UV at 254 nm]
t
R
8.0 min for 5d (98.7%); mp 96-98 °C; IR νmax (KBr)
3317, 3064, 3029, 3007, 1660, 1594, 1577, 1450, 1325, 1211,
-
1 1
2: GLC (condition 2) t
R
9.0 min for methyl 2,2-dimethyl-
876, 795, 718, 696, 681, 642 cm ; H NMR δ 7.99-7.96
13
1,3-dioxolane-4-carboxylate (96.2%; available from Aldrich
(m, 4H), 7.67-7.63 (m, 2H), 7.53-7.49 (m, 4H); C NMR
δ 194.5, 134.8, 132.9, 129.8, 129.0.
in enantiomerically pure forms); 7.5 min for 1b (0%); and
1
3.3 min for n-tridecane.
Procedures to Assess Effects of pH on the Oxidation
Ketopantoyl Lactone (Dihydro-4,4-dimethyl-2,3-furan-
dione) (5e). To a stirred mixture of pantolactone 4e
[dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanone; 2.60 g,
2
0
of 2-Octanol (4a) to 2-Octanone (5a) by the Quantitative
GLC Analysis: Procedure 3. 2-Octanol 4a (391 mg, 3.00
mmol) was subjected to the same oxidation conditions as
described for procedure 2. After the reaction mixture was
stirred at 30 °C for 3 h, i-PrOH (2.0 mL) was added with
water-cooling below 40 °C, and the stirring was continued
at 30 °C for 30 min to destroy the unconsumed TCCA.
AcOEt (10.0 mL) was added, and the mixture was stirred at
room temperature for 10 min. A 0.5 µL aliquot of the organic
phase was injected to a gas chromatograph running under
20.0 mmol], RuCl
mg, 0.40 mmol), AcONa (8.20 g, 100 mmol), and 1:1 MeCN/
O (40 mL) was added a solution of TCCA (4.64 g, 20.0
3 2
‚3H O (52.3 mg, 0.20 mmol), TBAB (129
H
2
mmol) in MeCN (20.0 mL) dropwise with water-cooling at
25-45 °C. The mixture was stirred at the same temperature
range for 1 h. i-PrOH (1.00 mL, 13.1 mmol) was added with
water-cooling below 45 °C, and the stirring was continued
for 1 h to destroy the unconsumed TCCA. The mixture was
filtered by the aid of Hyflo Super Cel to remove insoluble
materials. Layers of the filtrate were separated. The aqueous
layer was extracted with AcOEt (10 mL × 1). The combined
organic layers were washed with saturated aqueous NaCl
condition 1: t
.4 min for 4a.
-Octanone (5a). 2-Octanol 4a (390 mg, 2.99 mmol) was
R
4.4 min for n-tridecane, 5.3 min for 5b, and
6
2
subjected to the same conditions as those described for the
oxidation of 1a to 3a. The reaction was worked up and
solution (10 mL × 2), dried (MgSO
4
), and concentrated in
vacuo to give 5e (2.50 g) in 97.7% yield: mp 68-70 °C
2
0
analyzed quantitatively according to procedure 3: t
for n-tridecane, 5.3 min for 5b (98.4%), and 6.4 min for 4a
0%).
Cyclopentanone (5b). Cyclopentanol 4b (860 mg, 9.98
mmol) in 1:1 AcOEt/H O (20.0 mL) containing n-nonane
640 mg, 4.99 mmol; 0.5 equiv; an internal standard) was
treated with TCCA (0.67 M solution in ACOEt; 10.0 mL,
.71 mmol; 0.67 equiv) otherwise under the same conditions
R
4.4 min
(lit.: 66-67.5 °C); IR νmax (KBr) 3526, 2988, 2971, 2937,
1764, 1460, 1395, 1280, 1043, 1009, 991, 952, 940, 732
-
1
1
13
(
cm ; H NMR δ 4.48 (s, 2H), 1.33 (s, 6H); C NMR δ
198.1, 160.4, 77.0, 41.8, 22.0.
2,3:5,6-Di-O-isopropylidene-D-mannono-γ-lactone (5f).21
To a stirred mixture of 2,3:5,6-di-O-isopropylidene-R-D-
mannofuranose 4f (2.60 g, 9.99 mmol; available from
2
(
6
Aldrich), RuCl
mg, 0.20 mmol), AcONa (4.10 g, 50.0 mmol), and 1:1
MeCN/H O (20 mL) was added a solution of TCCA (2.32
3 2
‚3H O (26.2 mg, 0.10 mmol), TBAB (64.4
as those described for the oxidation of 1a to 3a. The reaction
was worked up and analyzed quantitatively according to
procedure 3 except that the GLC analysis was conducted
2
g, 9.98 mmol) in MeCN (10.0 mL) dropwise with water-
cooling at 25-45 °C. The mixture was stirred at the same
temperature range for 1 h. i-PrOH (500 µL, 6.57 mmol) was
added with water-cooling below 45 °C, and the stirring was
continued for 1 h to destroy the unconsumed TCCA. The
mixture was filtered by the aid of Hyflo Super Cel to remove
insoluble materials. Layers of the filtrate were separated. The
aqueous layer was extracted with AcOEt (5.0 mL × 1). The
combined organic layers were washed with saturated aqueous
under condition 2: GLC (condition 2) t
89.9%); 8.4 min for 4b (0%); 10.4 min for n-nonane.
Benzophenone (5c). Benzhydrol 4c (3.86 g, 20.0 mmol)
R
8.8 min for 5b
(
was oxidized in the presence of n-tridecane (1.84 g, 10.0
mmol; 0.5 equiv) as an internal standard otherwise under
the same conditions as those described for the oxidation of
R
4b to 5b: GLC (condition 2) t 6.8 min for 5c (95.4%);
21.5 min for n- tridecane; 22.2 min for 4c (0%).
Benzil (5d). To a stirred mixture of benzoin 4d (4.25 g,
NaCl solution (5.0 mL × 2), dried (MgSO
4
), and concen-
trated in vacuo to give 5f (1.35 g) in 52.3% yield: mp 124-
2
0.0 mmol), RuCl
mg, 0.40 mmol), K
3
‚3H
CO
O (40 mL) was added a solution of TCCA (3.09 g, 13.3
mmol) in AcOEt (20.0 mL) with water-cooling at 25-45
C. The mixture was stirred at the same temperature range
2
O (52.3 mg, 0.20 mmol), TBAB (129
2
1
2
3
(8.29 g, 60.0 mmol), and 1:1 AcOEt/
125 °C (lit.: 116 °C); IR νmax (KBr) 2991, 2939, 2893,
H
2
1784, 1382, 1259, 1216, 1153, 1121, 1084, 1042, 977, 856
-
1 1
cm ; H NMR δ 4.90-4.84 (m, 2H), 4.44-4.37 (m, 2H),
4.15 (dd, J ) 5.6 Hz, 9.2 Hz, 1H), 4.07 (dd, J ) 4.1 Hz, 9.2
Hz, 1H), 1.49 (s, 3H), 1.47 (s, 3H), 1.43 (s, 3H), 1.40 (s,
°
for 1 h. i-PrOH (1.00 mL, 13.1 mmol) was added with water-
cooling below 45 °C, and the stirring was continued for 1 h
to destroy the unconsumed TCCA. The mixture was filtered
by the aid of Hyflo Super Cel to remove insoluble materials.
Layers of the filtrate were separated, and the aqueous layer
was extracted with AcOEt (10 mL × 1). The combined
1
3
3H); C NMR δ 173.4, 114.4, 109.8, 78.1, 76.0, 75.8, 72.5,
+
66.4, 26.9, 26.7, 25.7, 25.1; MS m/z 281 [(M + Na) ].
Benzoic Acid (3c). To a stirred mixture of benzyl alcohol
1c (2.16 g, 20.0 mmol), RuCl
TBAB (129 mg, 0.40 mmol), K
3
‚3H
2
O (52.3 mg, 0.20 mmol),
(8.29 g, 60.0 mmol),
2
CO
3
Vol. 8, No. 6, 2004 / Organic Process Research & Development
•
937

and 1:1 MeCN/H
2
O (40.0 mL) was added a solution of
(70:30:0.1), 1.0 mL/min; detection, UV at 254 nm] t
min for 2c (99.6%).
R
8.0
TCCA (4.64 g, 20.0 mmol) in MeCN (20.0 mL) dropwise
with heating at reflux. The mixture was stirred and heated
at reflux for 1 h. The mixture was allowed to cool to room
temperature. i-PrOH (1.00 mL, 13.1 mmol) was added with
water-cooling below 45 °C, and the stirring was continued
for 1 h to destroy the unconsumed TCCA. The mixture was
filtered by the aid of Hyflo Super Cel to remove insoluble
materials. To the filtrate was added 5% aqueous HCl solution
to adjust its pH to 2.0. The layers were separated, and the
aqueous layer was extracted with AcOEt (10 mL × 1). The
combined organic layers were washed with saturated aqueous
Cinnamaldehyde (2d). To a stirred mixture of cynnamyl
alcohol 1d (2.68 g, 20.0 mmol), RuCl ‚3H O (52.3 mg, 0.20
mmol), TBAB (129 mg, 0.40 mmol), K CO (8.29 g, 60.0
mmol), and 1:1 AcOEt/H O (40.0 mL) was added a solution
3
2
2
3
2
of TCCA (3.09 g, 13.3 mmol) in AcOEt (20.0 mL) dropwise
with water-cooling at 25-45 °C. The mixture was stirred at
the same temperature range for 1 h. i-PrOH (1.00 mL, 13.1
mmol) was added with water-cooling below 45 °C, and the
stirring was continued for 1 h to destroy the unconsumed
TCCA. The mixture was filtered by the aid of Hyflo Super
Cel to remove insoluble materials. Layers of the filtrate were
separated, and the aqueous layer was extracted with AcOEt
(10 mL × 1). The combined AcOEt layers were washed with
saturated aqueous NaCl solution (10.0 mL × 2), dried
NaCl solution (10.0 mL × 2), dried (MgSO
trated in vacuo to give 3c (2.29 g) in 93.9% yield: HPLC
column, YMC-Pack ODS AM-302 (4.6 mm φ × 150 mm);
elution, H O/MeCN/CF CO H (70:30:0.1), 1.0 mL/min;
detection, UV at 254 nm] t 5.0 min for 3c (99.9%).
Benzaldehyde (2c). To a stirred mixture of benzyl alcohol
c (2.16 g, 20.0 mmol), RuCl ‚3H O (52.3 mg, 0.20 mmol),
TBAB (129 mg, 0.40 mmol), K CO (8.29 g, 60.0 mmol),
and 1:1 AcOEt/H O (40.0 mL) was added a solution of
4
), and concen-
[
2
3
2
R
(MgSO
98.5% yield: HPLC [column, YMC-Pack ODS AM-302
O/MeCN/CF CO
12.0
4
), and concentrated in vacuo to give 2d (2.60 g) in
1
3
2
(4.6 mm φ × 150 mm); elution, H
2
3
2
H
2
3
(70:30:0.1), 1.0 mL/min; detection, UV at 254 nm] t
min for 2d (95.5%).
R
2
TCCA (3.09 g, 13.3 mmol) in AcOEt (20.0 mL) dropwise
with water-cooling at 25-45 °C. The mixture was stirred at
the same temperature range for 1 h. i-PrOH (1.00 mL, 13.1
mmol) was added with water-cooling below 45 °C, and the
stirring was continued for 1 h to destroy the unconsumed
TCCA. The mixture was filtered by the aid of Hyflo Super
Cel to remove insoluble materials. Layers of the filtrate were
separated, and the aqueous layer was extracted with AcOEt
Acknowledgment
M.I. thanks Mr. Masafumi Moriwaki, Director, Research
& Development Center, Nagase & Co., Ltd., for his
managerial support. Thanks are also due to Mr. Yoshiaki
Okuda, Product Development Section 4, Bio/Fine Chemicals
Division, Nagase ChemteX Corporation, for his managerial
involvement in this joint program between Nagase & Co.,
Ltd. and Nagase ChemteX Corporation.
(
10 mL × 1). The combined AcOEt layers were washed with
saturated aqueous NaCl solution (10.0 mL × 2), dried
MgSO ), and concentrated in vacuo to give 2c (1.84 g) in
6.8% yield: HPLC [column, YMC-Pack ODS AM-302
4.6 mm φ × 150 mm); elution, H O/MeCN/CF CO
(
4
Received for review March 22, 2004.
OP049940K
8
(
2
3
2
H
938
•
Vol. 8, No. 6, 2004 / Organic Process Research & Development