Oxidation of ketone by palladium(II), α-hydroxyketone synthesis catalyzed by a bimetallic palladium(II) complex

Article abstract of DOI:10.1016/S0022-328X(02)01691-1

A bimetallic palladium(II) complex containing a triketone ligand and a bridging dinitrogen ligand oxidizes ketones in aqueous THF to α-hydroxyketone by a direct air oxidation. While the normal synthesis of α-hydroxyketones involves a series of reactions, this synthesis performs the transformation in one step in a catalytic air oxidation. This synthesis does not involve an olefin and is almost unprecedented in transition metal catalysis. Its main virtue is its simplicity and actually it is an enolization reaction. Methanesulfonic acid is used to accelerate the enolization of ketones. The reaction is carried out in the presence of CuCl₂ and/or dioxygen only. In particular, it is found that the hydroxyketone formation does not require the presence of CuCl₂. Matrix assisted laser desorption ionization (MALDI) and time-of-flight mass spectrometry (TOFMS) are used to record the mass spectra of α-hydroxyketones products. α-Cyano-4-hydroxycinnamic acid (CHCA) matrix promoted the molecular ion detection when 180 pmol of α-hydroxyketones is introduced into the TOFMS.

Full text of DOI:10.1016/S0022-328X(02)01691-1

Journal of Organometallic Chemistry 659 (2002) 50Á55
/
www.elsevier.com/locate/jorganchem
Oxidation of ketone by palladium(II). a-Hydroxyketone synthesis
catalyzed by a bimetallic palladium(II) complex
Arab K. El-Qisairi *, Hanan A. Qaseer
Department of Chemistry, Mu’tah University, PO Box 37, Mu’tah, Jordan
Received 14 March 2002; accepted 20 May 2002
Abstract
A bimetallic palladium(II) complex containing a triketone ligand and a bridging dinitrogen ligand oxidizes ketones in aqueous
THF to a-hydroxyketone by a direct air oxidation. While the normal synthesis of a-hydroxyketones involves a series of reactions,
this synthesis performs the transformation in one step in a catalytic air oxidation. This synthesis does not involve an olefin and is
almost unprecedented in transition metal catalysis. Its main virtue is its simplicity and actually it is an enolization reaction.
Methanesulfonic acid is used to accelerate the enolization of ketones. The reaction is carried out in the presence of CuCl2 and/or
dioxygen only. In particular, it is found that the hydroxyketone formation does not require the presence of CuCl2. Matrix assisted
laser desorption ionization (MALDI) and time-of-flight mass spectrometry (TOFMS) are used to record the mass spectra of a-
hydroxyketones products. a-Cyano-4-hydroxycinnamic acid (CHCA) matrix promoted the molecular ion detection when 180 pmol
of a-hydroxyketones is introduced into the TOFMS. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Palladium(II); Catalysis; Hydroxyketone
1. Introduction
carbonyl groupings, which are common structural
features of many natural products. Furthermore, a-
hydroxycarbonyl groupings are useful chiral building
units in the preparation of biologically active com-
pounds. The isomerization of a-hydroxycarbonyl com-
pounds is of crucial importance in metabolism [8].
The importance of a-hydroxyketones mentioned
above brought us to investigate and describe the
catalytic oxidation of ketones using achiral bimetallic
catalyst A, while the asymmetric version reactions are
now under processing [9].
The oxidation of carbonyl compounds by metal
species is a well-known and widely studied reaction
[1Á3]. Many of these apparently proceed by oxidation of
/
the enol tautomer. Thus, the oxidation of ketones by the
two-electron oxidants, Hg(II), Tl(III) and Mn(VII),
were postulated to involve the enol isomer [4]. Some
one-electron oxidants such as Mn(III) [5] and tris(1,10-
phenanthroline) complexes of Fe(III) and Ru(III) [6]
also attack the enol isomer. Recently, palladium(II)
chloride has been used in the catalytic carbonylation of
ketones [7].
A number of important compounds that show inter-
esting pharmacological properties possess a-hydroxy-
* Corresponding author. Tel.: ꢀ
/
962-6-461-7890x4610; fax: ꢀ962-6-
/
465-4061
E-mail addresses: aqaseer@mutah.edu.jo, aqaseer@yahoo.com
(H.A. Qaseer).
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 6 9 1 - 1

A.K. El-Qisairi, H.A. Qaseer / Journal of Organometallic Chemistry 659 (2002) 50Á
/
55
51
2. Experimental
stirrer was turned on to start the reaction. The pressure
was kept constant at 1 atm. by continuously leveling the
mercury in the gas buret and bulb. Gas uptake readings
were taken at regular intervals. The reaction was
allowed to run until the reaction mixture was at least
0.25 M in total oxidation product. The oxidation
product was separated from the reaction mixture by
continuous extraction with ether over night. The ether
was dried over anhydrous MgSO4 and removed by
distillation. Analysis of the product was carried out by
GLC, MS, FTIR, and 1H- and 13C-NMR. In every
2.1. Materials
All solvents used were analytical grade reagents.
Tetrakis(acetonitrile)palladium (II) tetrafluoroborate
{[Pd(MeCN)4](BF4)2} was purchased from Strem Che-
micals. 1,2-Diaminocyclohexane (DACH) and all start-
ing materials for the triketone ligand and all ketones
were obtained from Aldrich Chemical Co. The triketone
ligand, 1-phenyl-1,3,5-hexanetione (PHT) was prepared
as before [10]. Diacetonitrile-1-phenyl-1,3,5-hexane-
trione-m-1,2-diaminocyclohexanedipalladium(II) tetra-
reaction, 8Á15% of the starting material was recovered.
/
The percent yields based on the amount of dioxygen
uptake for all runs.
fluoroborate
{[Pd2(MeCN)2(PHT)(DACH)](BF4)2}
was synthesized by a similar procedure described for
the chiral analogue [10] and characterized by 1H-
and13C-NMR.
2.3.1. Hydroxylation of cyclohexanone
Oxidation of cyclohexanone by the procedure de-
scribed above afforded only one product in a 90% yield.
2.2. Instrumentation
GLC and 1H- and 13C-NMR identified the product as 2-
All 1H- and 13C-NMR spectra were recorded on a 400
MHz Varian VXR 400 spectrometer using CDCl3.
Chemical shifts for 1H and 13C are relative to
(CH3)4Si. Measurements were performed at ambient
probe temperature using 5 mm o.d. sample tubes. GLC
analyses were carried out on a GOW-MAC gas chro-
matograph (Model 350). IR spectra were recorded on an
ATI Mattson Genesis series FTIR spectrometer. Mole-
cular weight spectra were acquired using a modified
hydroxy cyclohexanone. m/zꢁ
MHz, CDCl3): dꢁ1.66Á
2H), 2.75Á2.82 (m, OH), 4.35 (ddd, 1H, Jꢁ
8.65 Hz) ppm. 13C-NMR (100 MHz, CDCl3): dꢁ
27.1, 37.4, 39.3, 62.8, 203.0 ppm. FTIR (neat): 3146,
2969, 1790, 1716, 1383, 1097 cmꢂ1
/
114.139. H-NMR (400
1
/
/
2.10 (m, 6H), 2.30Á
1.10, 5.08,
22.9,
/
2.40 (m,
/
/
/
.
2.3.2. Hydroxylation of 2-methylcyclohexanone
WileyÁ
/
McLaren design ‘time-of-flight mass spectrome-
This oxidation afforded two products in relative
yields of 86 and 14%, respectively, and in a chemical
yield 85%. 1H- and 13C-NMR identified the products as
6-methyl-2-hydroxycyclohexanone, and 2-methylcyclo-
hex-2-en-1-one, respectively. Spectral data of the
products were as follows. 6-methyl-2-hydroxycyclohex-
try’ (TOFMS) (model D850, R. M. Jordan Co., Grass
Valley, CA) in the linear mode. A nitrogen laser (337
nm, 5 mW peak laser power, 3 ns pulse width, and a
Â
400 mm2 spot size) was used to induce desorption
/
(model VSL-337ND, Laser Science, Newton, MA).
Samples preparation for MS were conducted as de-
scribed before [11].
anone: m/zꢁ
dꢁ1.04 (d, 3H, Jꢁ
2H), 1.93Á2.07 (m, 1H), 2.10Á
(m, 2H), 2.56 (dd, 1H, Jꢁ 5.08, 8.65 Hz), 4.22 (t, 1H,
Jꢁ
7.38 Hz) ppm. 13C-NMR (100 MHz, CDCl3): dꢁ
/
128.165. 1H-NMR (400 MHz, CDCl3):
6.8 Hz), 1.55 (d, OH), 1.71Á1.79 (m,
2.19 (m, 1H), 2.20Á2.30
/
/
/
/
/
/
2.3. General procedure for the catalytic oxidation of
ketones
/
/
/
21.7, 28.1, 33.9, 34.3, 44.9, 60.4, 204.1 ppm. FTIR
(neat): 3150, 2973, 1796, 1717, 1383, 1097 cmꢂ1. 2-
methyl cyclohex-2-en-1-one: 1H-NMR (400 MHz,
In a typical experiment a 250-ml two-necked cone
shaped flask, with indented sides to increase the
efficiency of stirring, was equipped with a magnetic
stirring bar, subseal septum and vacuum adapter. The
flask was charged with 15 ml of H2O, 15 ml of THF,
2.00 g (14.9 mmol) of CuCl2, 0.70 g (7.3 mmol) of
CH3SO3H, and 0.10 mmol of catalyst. The flask was
then placed in a constant-temperature bath at 25 8C
and connected to the gas uptake system [10,12]. The
system was evacuated for 10 min on the vacuum line
with the stirrer running. The stirring was stopped and
the system pressurized to 1 atm. with dioxygen. Then 8
mmol of ketone was added to the reaction mixture by
syringe. The mercury in the gas buret and the leveling
bulb were equalized, and a reading was taken. The
CDCl3): dꢁ
Jꢁ 5.70 Hz), 2.52 (t, 1H, Jꢁ
4.76 Hz) ppm. 13C-NMR (100 MHz, CDCl3): dꢁ
/
1.86 (s, 3H), 1.97 (m, 2H), 2.43 (q, 2H,
7.0 Hz), 5.93 (t, 1H, Jꢁ
23.0,
/
/
/
/
24.4, 38.9, 44.9, 116.3, 151.5, 194.4 ppm.
2.3.3. Hydroxylation of cyclopentanone
Hydroxylation of cyclopentanone gave 2-hydroxycy-
1
clopentanone in a 92% yield. m/zꢁ
(400 MHz, CDCl3): dꢁ1.66 (br.s, OH), 1.90Á
6H), 4.10 (t, 1H, Jꢁ NMR (100
7.35 Hz) ppm. 13CÁ
MHz, CDCl3): dꢁ19.3, 33.5, 35.1, 58.3, 210.8 ppm.
FTIR (neat): 3153, 2970, 1790, 1721, 1386, 1089 cmꢂ1
/100.113. H-NMR
/
/2.30 (m,
/
/
/
.

52
A.K. El-Qisairi, H.A. Qaseer / Journal of Organometallic Chemistry 659 (2002) 50Á55
/
2.3.4. Hydroxylation of 2-butanone
0.95 (t, 3H, Jꢁ
(m, 2H), 2.14 (br.s, OH), 2.52 (t, 2H, Jꢁ
(s, 2H) ppm. 13C-NMR (100 MHz, CDCl3): dꢁ
/
7.40 Hz), 1.32Á
/
1.54 (m, 2H), 1.75Á
7.30 Hz), 4.10
14.0,
/
1.92
Hydroxylation of 2-butanone gave 3-hydroxy-2-buta-
none, and 1-hydroxy-2-butanone in relative yields of
78%, and 22%, respectively, and in a chemical yield 94%.
/
/
22.3, 28.4, 39.4, 71.4, 194.6 ppm.
Spectral data for 3-hydroxy-2-butanone: m/zꢁ
1H-NMR (400 MHz, CDCl3): dꢁ
1.60 (d, 3H, Jꢁ
Hz), 2.32 (s, 3H), 3.73 (s, OH), 4.30 (q, 1H, Jꢁ6.2 Hz)
ppm. 13C-NMR (100 MHz, CDCl3): dꢁ
20.2, 25.8, 59.1,
/
88.105.
/
/
6.8
/
2.3.7. Hydroxylation of 4-heptanone
/
Hydroxylation of 4-heptanone afforded only one
product in a 93% yield. A pure sample was isolated by
preparative GC and identified as 3-hydroxy-4-hepta-
and 187.8 ppm. FTIR (neat): 3150, 2973, 1796, 1717,
1383, 1097 cmꢂ1. Data for 1-hydroxy-2-butanone: m/
1
zꢁ
/
88.103. H-NMR (400 MHz, CDCl3): dꢁ
/1.10 (t,
none. m/zꢁ
0.91 (t, 3H, Jꢁ
(m, 2H), 1.80 Á
2H, Jꢁ7.29 Hz), 4.12 (dd, 1H, Jꢁ
13C-NMR (100 MHz, CDCl3): dꢁ
10.6, 13.6, 17.1, 27.2,
40.6, 65.2, 205.4 ppm. FTIR (neat): 3151, 2974, 1794,
1716, 1383, 1096 cmꢂ1
/
130.180. 1H-NMR (400 MHz, CDCl3): dꢁ
7.40 Hz), 1.00 (t, 3H, Jꢁ7.35 Hz), 1.63
2.05 (m, 2H), 2.15 (br.s, OH), 2.61 (t,
5.60, 8.12 Hz) ppm.
/
3H), 2.15 (br.s, OH), 2.63 (q, 2H), and 4.07 (s, 2H) ppm.
8.4, 32.6, 61.4, and
13C-NMR (100 MHz, CDCl3): dꢁ
195.6 ppm.
/
/
/
/
/
/
/
2.3.5. Hydroxylation of 3-pentanone
Oxidation of 3-pentanone afforded only one product
.
1
in a 91% yield. GLC and H- and 13C-NMR identified
the product as 2-hydroxy-3-pentanone. m/zꢁ
1H-NMR (400 MHz, CDCl3): dꢁ
1.08 (t, 3H, Jꢁ
Hz), 1.57 (d, 3H, Jꢁ6.2 Hz), 2.38 (d, OH), 2.61 (dq,
1H), 2.75 (dq, 1H), 4.34 (q, 1H) ppm. 13C-NMR (100
/
102.130.
/
/
7.20
2.4. Control experiments
/
To confirm that the bimetallic catalyst is the actual
catalyst, two control experiments were carried out. First,
the oxidation of cyclohexanone was attempted using all
reactants except the bimetallic catalyst. The results have
shown that there was no oxygen uptake and no
hydroxyketone product was detected by GLC. Second,
the reaction was done until the usual amounts of
product were accumulated. The catalyst was isolated
from the reaction mixture as the bromide compound. It
was proved to be the bimetallic catalyst by 1H- and 13C-
NMR analysis. A third experiment was carried out using
dioxygen instead of CuCl2. The result indicated the
formation of hydroyketone in a high yield and the
catalyst is recovered. This control experiment indicated
that oxidation is an air oxidation and does not require
the presence of CuCl2.
MHz, CDCl3): dꢁ8.0, 20.4, 31.7, 58.4, 206.0 ppm.
/
FTIR (neat): 3154, 2972, 1793, 1719, 1383, 1095 cmꢂ1
.
2.3.6. Hydroxylation of 2-hexanone
Hydroxylation of 2-hexanone gave two products in
relative yields of 88 and 12%, respectively, and in a
1
chemical yield 88%. H- and 13C-NMR identified the
products as 3-hydroxy-2-hexanone, and 1-hydroxy-2-
hexanone, respectively. Spectral data for 3-hydroxy-2-
hexanone: m/zꢁ
dꢁ0.93 (t, 3H, Jꢁ
1.96 (m, 2H), 2.10 (br.s, OH), 2.29 (s, 3H), 4.14 (dd, 1H,
Jꢁ
5.59, 8.52 Hz) ppm. 13C-NMR (100 MHz, CDCl3):
dꢁ13.4, 19.3, 25.8, 35.8, 64.0, 203.4 ppm. FTIR (neat):
3158, 2980, 1788, 1720, 1383, 1096 cmꢂ1. Data for 1-
hydroxy-2-hexanone: 1H-NMR (400 MHz, CDCl3): dꢁ
/
116.155. 1H-NMR (400 MHz, CDCl3):
/
/
7.40 Hz), 1.35Á
/
1.56 (m, 2H), 1.75Á
/
/
/
/
Table 1
Catalytic hydroxylation of ketones in aqueous THF by dipalladium catalyst in the presence of CuCl2
a
b
Run Ketone
Products (relative yields)
Yield (%)
1
2
3
4
5
6
7
Cyclohexanone
2-Hydroxycyclohexanone
6-Methyl-2-hydroxycyclohexanone (86%), 2-methylcyclohex-2-en-1-one (14%)
2-Hydroxycyclopentanone
90
85
92
94
91
88
93
2-Methylcyclohexanone
Cyclopentanone
2-Butanone
3-Hydroxy-2-butanone (78%), 1-hydroxy-2-butanone (22%)
2-Hydroxy-3-pentanone
3-Pentanone
2-Hexanone
4-Heptanone
3-Hydroxy-2-hexanone (88%), 1-hydroxy-2-hexanone (12%)
3-Hydroxy-4-heptanone
All runs contain 0.08Á0.1 mmol of dipalladium catalyst in 30 ml of solvent and are 0.5 M in CuCl2 and 0.2 M in CH3SO3H. Temperature: 25 8C.
/
The solvent was a H2OÁ
/
THF mixture.
The relative yields were determined by GLC analysis.
a
b
The yield was determined based on O2 uptake using gas burets and assuming O2 is a four-electron oxidant. Turnovers were in the range 180Á200.
/

A.K. El-Qisairi, H.A. Qaseer / Journal of Organometallic Chemistry 659 (2002) 50Á
/
55
53
Scheme 1.
3. Results and discussion
carbonylation of ketones catalyzed by palladium(II)
chloride [7].
Previous studies on the oxidation of internal olefins
under the chlorohydrin conditions have shown, in
addition to the ketones produced by the Wacker
oxidation, that hydroxyketones were also obtained
[10]. This result encourages us to investigate comple-
mentary reactions using ketones as substrates instead of
internal olefins.
The symmetrical ketones namely, cyclohexanone,
cyclopentanone, 3-pentanone, and 4-heptanone afford
only one product (4, Scheme 2) (Table 1) which results
from one expected enol form (3, Scheme 2). Scheme 2
represents the reaction using cyclohexanone as a sub-
strate.
Whereas the unsymmetrical ketones namely, 2-
methylcyclohexanone, 2-butanone, and 2-hexanone
gave two products (Table 1) resulted from the two
possible enols (5a, 5b) forms as indicated in Scheme 3.
Scheme 3 illustrates the reaction using 2-butanone as a
substrate. Compound 6a is found to be the major
product rather than compound 6b. This result may be
explained by the formation of the most stable enol form
(5a). Since the reaction is an enolization, it would be
expected to be acid catalyzed. Methanesulfonic acid was
used in all reactions to accelerate the enolization of
ketone. The oxidation becomes faster and gave almost
quantitative yields.
The hydroxylation of ketones by dipalladium(II) is a
new method used to prepare a-hydroxyketones. Since
the normal synthesis of chiral a-hydroxyketones in-
volves a series of reactions [13,14]. The present synthesis
performs the transformation in one step in a catalytic air
oxidation. However, the asymmetric syntheses of a-
hydroxyketones by using chiral bimetallic catalyst are
underway [9]. In particular, the formation of a-hydro-
xyketone does not require the presence of CuCl2. The
reaction of ketone was run with a bimetallic catalyst A
in chloride-free media using dioxygen as a reoxidant and
gave the desired a-hydroxyketones in high yield.
The characterizations of the a-hydroxyketones pro-
ducts were achieved by using spectroscopic techniques
1
such as H-, 13C-NMR, FTIR and MS (see Section 2).
The a-hydroxyketones products, namely 2-hydroxycy-
clohexanone, 6-methyl-2-hydroxycyclohexanone, 2-
hydroxycyclopentanone, 3-hydroxy-2-butanone, 2-hy-
droxy-3-pentanone and 3-hydroxy-2-hexanone products
all prepared in Â
/
85Á92% yield. The products distribu-
/
tion and the percentage yields are summarized in Table
1. On the other hand, the other minor products, namely
2-methylcyclohex-2-en-1-one (2, Scheme 1), 1-hydroxy-
2-butanone, and 1-hydroxy-2-hexanone, are produced
in low yields (Table 1). The route for the formation of 2-
methylcyclohex-2-en-1-one (2) is shown in Scheme 1 and
most likely due to the elimination of water from the a-
hydroxyketone (1). Previously, a similar result was
obtained by the same mechanism in a study of
Scheme 2.
Scheme 3.

54
A.K. El-Qisairi, H.A. Qaseer / Journal of Organometallic Chemistry 659 (2002) 50Á
/
55
Scheme 4.
[3] W.J. De Klein, in: W.J. Mijs, C.R.H.I. De Jonge (Eds.), Organic
Synthesis by Oxidation with Metal Compounds, Plenum Press,
The bimetallic complex, A, is analogous to the
catalysts previously employed for the asymmetric chlo-
hydrin synthesis [10]. Of course in the chlorohydrin
synthesis, the chelating bimetallic ligand was chiral. As
shown in Scheme 4 using 3-pentanone oxidation as an
example, the reason for this air oxidation capability is
that Pd(I) dimer, rather than Pd(0), is the reduced
species. This Pd(I) dimer is readily oxidized back to the
Pd(II) dimer before Pd(0) can form. Similar results were
observed in previous reported studies [15].
New York, 1986, pp. 261Á314.
/
[4] (a) J. S. Litter, J. Chem. Soc. (1962) 827, 832;
(b) J. S. Litter, J. Chem. Soc. (1964) 2722.
[5] (a) H.J. den Hertog, Jr, E.C. Kooyman, J. Catal. 6 (1966) 347,
357;
(b) E.I. Heiba, R.M. Dessau, J. Am. Chem. Soc. 93 (1971) 524.
[6] (a) F.T.T. Ng, P.M. Henry, J. Am. Chem. Soc. 98 (1976) 3606;
(b) F.T.T. Ng, P.M. Henry, Can. J. Chem. 55 (1977) 2900.
[7] (a) O. Hamed, A. El-Qisairi, P.M. Henry, Tetrahedron Lett. 41
(2000) 3021;
(b) O. Hamed, A. El-Qisairi, P.M. Henry, J. Org. Chem. 66 (2001)
180.
[8] H. Brunner, F. Stohr, Eur. J. Org. Chem. (2000) 2777 and
¨
In conclusion, we have developed a novel hydroxyla-
tion of ketones since it does not involve an olefin and is
almost unique in transition metal catalysis.
references cited therein.
[9] A. El-Qisairi, Unpublished results.
[10] A. El-Qisairi, P.M. Henry, J. Organomet. Chem. 603 (2000) 50.
[11] A. El-Qisairi, Spectroscopy 16 (2002) 37.
[12] For similar apparatus see: P.M. Henry, Palladium Catalyzed
Oxidation of Hydrocarbon, D. Reidel, Dordrecht, Holland, 1980,
p. 57.
Acknowledgements
We are grateful to Professor P.M. Henry for allowing
us to use his laboratory to conduct this work of research
and using the instruments provided by the Department
of Chemistry, Loyola University Chicago, IL. The
authors would also like to thank Professor M. Paul
Chiarelli for his assistance in doing the Mass-spectra at
his Laboratory, Department of Chemistry, Loyola
University Chicago, IL.
[13] (a) For examples of preparation of active a-hydroxyketones and
their derivatives, see: E. Vedejs, J.E. Telschow, J. Org. Chem. 43
(1978) 188;
(b) E. Vedejs, S. Larsen, Org. Synth. 64 (1985) 127;
(c) T. Cuvigny, G. Valette, M. Larcheveque, H. Normant, J.
Organomet. Chem. 155 (1978) 147;
(d) F.A. Davis, L.C. Vishwakarma, J.M. Billmers, J. Finn, J. Org.
Chem. 49 (1984) 3241;
(e) R.M. Moriarty, K.C. Hou, Tetrahedron Lett. 25 (1984) 691;
(f) N.K. Dunlap, M.R. Sabol, D.S. Watt, Tetrahedron Lett. 25
(1984) 5839;
References
(g) G.M. Rubottom, J.M. Gruber, Jr, H.D. Juve, D.A. Chaleson,
Org. Synth. 64 (1985) 118;
[1] J. Rocˇek, in: S. Patai (Ed.), The Chemistry of the Carbonyl
Group, Ch. 10, Wiley, New York, 1966.
(h) C. Iwata, Y. Takemoto, A. Nakamura, T. Imanishi, Tetra-
hedron Lett. 26 (1985) 3227;
[2] H.S. Verter, in: S. Patai (Ed.), The Chemistry of the Carbonyl
Group, Ch. 10, vol. 2, Wiley, New York, 1970.
(i) R.V. Hoffmann, C.S. Carr, B.C. Jankowski, J. Org. Chem. 50
(1985) 5148;

A.K. El-Qisairi, H.A. Qaseer / Journal of Organometallic Chemistry 659 (2002) 50Á
/
55
55
(j) R.M. Moriarty, O. Prakash, M.P. Duncan, K. Vaid, J. Org.
Chem. 52 (1987) 150;
(c) T. Dunnwald, M. Muller, J. Org. Chem. 65 (2000) 8608;
(d) T. Koike, K. Murata, T. Ikariya, Org. Lett. 2 (2000) 3833;
(k) F.A. Davis, A.C. Sheppard, J. Org. Chem. 52 (1987) 955.
[14] (a) For leading references on enzymatic and nonenzymatic
synthesis of enantiomerically enriched hydroxyketones and their
derivatives, see: Y. Zhu, L. Shu, Y. Tu, Y. Shi, J. Org. Chem. 66
(2001) 1818 (and references cited therein);
(e) P. Magnus, A.H. Payne, M.J. Waring, D.A. Scott, V. Lynch,
Tetrahedron Lett. 41 (2000) 9725.
[15] (a) K. Zaw, P.M. Henry, J. Mol. Catal. A 101 (1995) 187;
(b) P.M. Henry, X. Ma, G. Noronha, K. Zaw, Inorg. Chem. Acta
240 (1995) 205;
(b) S. Muthusamy, S.A. Babu, C. Gunanathan, R.V. Jasara,
Tetrahedron Lett. 42 (2001) 5113;
(c) G. Noronha, P.M. Henry, J. Mol. Catal. A 120 (1997) 75.