Polystyrene-supported (catecholato)oxorhenium complexes: Catalysts for alcohol oxidation with DMSO and for deoxygenation of epoxides to alkenes with triphenylphosphine

Article abstract of DOI:10.1002/1522-2675(200210)85:10<3225::AID-HLCA3225>3.0.CO;2-H

Polymer-supported catalysts offer practical advantages for organic synthesis, such as improved product isolation, ease of catalyst recycling, and compatibility with parallel solution-phase techniques. We have developed the (carboxypolystyrene-catecholato)rhenium catalyst 2 derived from tyramine (=4-(2-amino-ethyl)phenol), which is effective for alcohol oxidation with dimethylsulfoxide (DMSO) and for epoxide deoxygenation with triphenylphosphine. The supported [Re(catecholato)]catalyst 2 is air- and moisture-stable and can be recovered and used repeatedly without decreasing activity. The procedures work with non-halogenated solvents (toluene). DMSO for Re-catalyzed alcohol oxidation is inexpensive and safer for transport and storage than commonly used peroxide reagents. The oxidation procedure was best suited for aliphatic alcohols, and the mild conditions were compatible with unprotected functional groups, such as those of alkenes, phenols, nitro compounds, and ketones (see Tables 1 and 2). Selective oxidation of secondary alcohols in the presence of primary alcohols was possible, and with longer reaction time, primary alcohols were converted to aldehydes without overoxidation. Epoxides (oxirans) were catalytically deoxygenated to alkenes with this catalyst and Ph₃P (see Table 3). Alkyloxiranes were converted to the alkenes with retention of configuration, while partial isomerization was observed in the deoxygenation of cis-stilbene oxide (cis-1.2-diphenyloxirane). These studies indicate that supported [Re(catecholato)] complexes are effective catalysts for O-atom-transfer reactions, and are well suited for applications in organic synthesis.

Full text of DOI:10.1002/1522-2675(200210)85:10<3225::AID-HLCA3225>3.0.CO;2-H

Helvetica Chimica Acta Vol. 85 (2002)
3225
Polystyrene-Supported (Catecholato)oxorhenium Complexes: Catalysts for
Alcohol Oxidation with DMSO and for Deoxygenation of Epoxides to
Alkenes with Triphenylphosphine
by Jeffrey B. Arterburn*, Minghua Liu1), and Marc C. Perry2)
Department of Chemistry and Biochemistry MSC 3C, New Mexico State University, Box 30001,
Las Cruces, NM 88003, USA
(e-mail: jarterbu@nmsu.edu)
Dedicated to Professor Dieter Seebach on the occasion of his 65th birthday
Polymer-supported catalysts offer practical advantages for organic synthesis, such as improved product
isolation, ease of catalyst recycling, and compatibility with parallel solution-phase techniques. We have
developed the (carboxypolystyrene-catecholato)rhenium catalyst 2 derived from tyramine (ˆ4-(2-amino-
ethyl)phenol), which is effective for alcohol oxidation with dimethylsulfoxide (DMSO) and for epoxide
deoxygenation with triphenylphosphine. The supported [Re(catecholato)]catalyst 2 is air- and moisture-stable
and can be recovered and used repeatedly without decreasing activity. The procedures work with non-
halogenated solvents (toluene). DMSO for Re-catalyzed alcohol oxidation is inexpensive and safer for
transport and storage than commonly used peroxide reagents. The oxidation procedure was best suited for
aliphatic alcohols, and the mild conditions were compatible with unprotected functional groups, such as those of
alkenes, phenols, nitro compounds, and ketones (see Tables 1 and 2). Selective oxidation of secondary alcohols
in the presence of primary alcohols was possible, and with longer reaction time, primary alcohols were converted
to aldehydes without overoxidation. Epoxides (oxirans) were catalytically deoxygenated to alkenes with this
catalyst and Ph3P (see Table 3). Alkyloxiranes were converted to the alkenes with retention of configuration,
while partial isomerization was observed in the deoxygenation of cis-stilbene oxide (cis-1,2-diphenyloxirane).
These studies indicate that supported [Re(catecholato)] complexes are effective catalysts for O-atom-transfer
reactions, and are well suited for applications in organic synthesis.
Introduction. The development of supported catalysts is an area of great interest
and offers numerous practical applications in organic synthesis. Several excellent
review articles on the topic of supported catalysts in organic chemistry have recently
appeared [1 7]. The use of polymer-supported ligands for modifying homogeneous
metal-catalyzed reactions to operate as heterogeneous systems provides significant
advantages, e.g., simple product isolation and the possibility of catalyst recycling. This
approach has been highly successful for catalytic reductions, oxidations, and CÀC bond
forming reactions [1 7]. The use of supported chiral ligands for enantioselective CÀC
bond forming reactions is an area of particular importance [8 15].
The oxidation of alcohols to aldehydes or ketones is a fundamental transformation
that remains an active area of research because of the increasing demand for processes
that involve safe, economical reagents, avoid hazardous solvents, minimize waste by-
1
)
Current address: Metabasis Therapeutics, Inc., 9390 Towne Centre Dr., Bldg. 300, San Diego, CA 92121,
USA.
2
)
Current address: Department of Chemistry, Texas A & M University, College Station, TX 77840, USA.

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Helvetica Chimica Acta Vol. 85 (2002)
products, and satisfy requirements for chemoselectivity. Polymer-supported reagents/
catalysts for alcohol oxidation are particularly important for applications in parallel
solution-phase synthesis, where product purification can be facilitated by simple
filtration. Recently, a derivative of the widely used periodinane oxidant 2-iodoxyben-
zoic acid was rendered heterogeneous by attachment to a polystyrene support, and this
reagent was used for the oxidation of various alcohols [16]. Immobilized 2,2,6,6-
tetramethylpiperidin-1-yloxyl (TEMPO) nitroxyl radicals were shown to be efficient
catalysts for alcohol oxidation with hypochlorite, and preferential selectivity for
primary alcohols in the presence of secondary alcohols was exhibited [17 19]. A
polymer-bound bromite reagent was used for alcohol oxidation together with a
catalytic amount of TEMPO [20]. A variety of polymer-supported transition metal
complexes have been used for alcohol oxidation. Chlorochromate imidazolium
reagents, e.g., oxidized benzylic and allylic alcohols [21]. Polystyrene-supported
[CoII(PPh3)] catalyzed the oxidation of benzylic and allylic alcohols with tert-butyl
hydroperoxide, but was not effective for aliphatic alcohols [22]. A related system
t
using a supported (phosphine)ruthenium complex with BuOOH oxidized aliphatic
alcohols and hydrocarbons to ketones, and also catalyzed transfer hydrogena-
tion from propan-2-ol [23]. Polymer-supported perruthenate efficiently catalyzed
the oxidation of primary and secondary benzylic alcohols, but did not oxidize
secondary aliphatic alcohols [24 27]. Polymer-supported 4-methylmorpholine 4-
oxide has been used as the co-oxidant in the perruthenate-catalyzed oxidation of
alcohols [28].
Rhenium complexes catalyze a variety of synthetically useful reactions, and a great
deal of interest has focused on homogeneous peroxide/methyltrioxorhenium ([Re-
(Me)O3]; MTO) catalyzed oxidations [29 33]. Recently, a heterogeneous poly(4-
vinylpyridine)/MTO/H2O2 system was used for the catalytic epoxidation of alkenes
[34]. Our laboratory has investigated a variety of homogeneous ReV-catalyzed O-atom-
transfer reactions using sulfoxides as O-donors [35 37]. Sulfoxides such as DMSO are
readily-available, economical, and stable oxidants. The Swern oxidation of alcohols
relies on DMSO but requires anhydrous solvents, low temperatures, an amine base, and
a stoichiometric amount of a strong electrophilic activating agent, e.g., oxalyl chloride
[38]. Sulfoxides are also effective oxo-transfer agents capable of producing oxometal
complexes; however, few examples of transition-metal-catalyzed alcohol oxidations
with sulfoxides have been reported, and most are limited to easily oxidizable benzylic
and allylic substrates [39 41]. We recently reported a rhenium-catalyzed alcohol
oxidation with methylsulfoxide in ethylene glycol/toluene, which produced the
corresponding ketals in high yields [42]. The presence of ethylene glycol was required
for the generation of an active catalyst, which suggested the possible in situ formation of
a rhenium complex containing a coordinated diol ligand. Subsequent studies in our
laboratory have investigated catechols (benzene-1,2-diols) as potential ligands for
rhenium-catalyzed alcohol oxidation with DMSO, and we found that 5% [Re-
Cl3(O)(PPh3)2]/catechol/DMSO was an efficient homogeneous system for alcohol
oxidation [43]. These results led us to investigate polymer-supported (catecholato)-
rhenium complexes as heterogeneous catalysts for O-transfer reactions. Herein, we
describe the synthesis of a polystyrene-supported Re catalyst with a tyramine-derived
ligand (tyramine ˆ 4-(2-aminoethyl)phenol) and report synthetically useful applica-

Helvetica Chimica Acta Vol. 85 (2002)
3227
tions for the oxidation of alcohols with DMSO, as well as the reduction of epoxides to
alkenes with PPh3.
Results and Discussion. Polymer-Supported Rhenium Catalyst. The immobilized
catecholato ligand was prepared by coupling 3-hydroxytyramine to commercially
available carboxypolystyrene (Novabiochem, 100 200 mesh, 1% divinylbenzene,
loading capacity 1.24 mmol gÀ1) in the presence of (1H-benzotriazol-1-yloxy)tri(pyr-
rolidin-1-yl)phosphonium hexafluorophosphate (PyBOP) and EtNiPr2 in CH2Cl2
(Scheme 1). The course of the reaction was monitored by FT-IR by observing the
disappearance of the carboxy absorbance at 1688 cmÀ1. The resulting polystyrene-
supported catechol was allowed to react with the oxorhenium complex [Re-
Cl3(O)(PPh)2] and DMSO in toluene, and heated to reflux for 1 h. The polymer-
supported (catecholato)rhenium complex 1 was isolated by filtration, and the resin
rinsed thoroughly with CH2Cl2. It exhibited a strong IR absorbance at 908 cmÀ1,
characteristic of the ReˆO oxo group. The complex retained a triphenylphosphine
oxide ligand (vide infra), and the FT-IR spectra were consistent with a (monochloro)-
(monooxo)rhenium(V) complex containing a coordinated sulfoxide ligand. Dimethyl-
sulfide was produced when the polymer complex was heated in refluxing toluene and is
expected to produce the corresponding dioxorhenium(VII) complex. The structures of
several (catecholato)rhenium [44 46] and bis(catecholato) complexes [47 49] have
been reported, and 1 (ReV) is closely related to the known complex [Re-
Cl(C6H4O2)(O)(PPh3)2] by substitution of the phosphine ligands with a phosphine
oxide and sulfoxide ligand [45]. Ongoing studies with simple catecholato ligands are
currently in progress in our laboratory and are expected to provide more detailed
structural information.
Scheme 1
Alcohol Oxidation. The polymer-bound complex 1 was found to be an active
catalyst for the oxidation of propan-2-ol with DMSO, producing acetone, H2O, and
Me2S, as shown in Scheme 2. A small amount of triphenylphosphine oxide, corre-
sponding to the quantity of polystyrene-supported Re-complex 1, was also released as a
labile ligand from the original complex during the alcohol oxidation reaction, and was

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Helvetica Chimica Acta Vol. 85 (2002)
isolated in the filtrate from the reaction mixture. A working hypothesis for the catalytic
cycle of this reaction is shown in Scheme 2. The (alcohol)rhenium(VII)dioxo complex
2a undergoes oxidation of the secondary-alcohol CÀH to produce the (ketone)rhe-
nium(V) complex 2b. Displacement of the labile ketone and H2O ligands by additional
alcohol and DMSO would form 2d. Oxidation of ReV to ReVII by the coordinated
sulfoxide ligand would then generate 2a and resume the cycle. The polystyrene-
supported complex 2 isolated from the propan-2-ol oxidation retained its catalytic
activity for alcohol oxidation and was stable to storage at room temperature for months
without observable decomposition. Subsequent oxidations of propan-2-ol using
recovered 2 proceeded equally well under these conditions. The product was free
from additional triphenylphosphine oxide, a significant advantage for preparative
purification. These results led us to treat the catalyst 1 with propan-2-ol in refluxing
toluene as a standard protocol to produce catalyst 2, which was investigated next.
Scheme 2
A variety of alcohols were oxidized in good to excellent yields in the presence of
polymer-supported catalyst 2, as shown in Table 1. A typical procedure involved
refluxing a 0.2m solution of alcohol substrate in toluene with 5% of catalyst 2 and 1.5
equiv. of DMSO. The removal of H2O was facilitated by a Dean-Stark trap. No
precautions to exclude air were necessary. The products were isolated by filtration to
remove the heterogeneous catalyst, followed by an aqueous wash to remove DMSO.
Secondary alcohols were oxidized at significantly faster rates than primary ones, as
shown by comparing the times required for complete oxidation of dodecan-1-ol and -2-
ol (Entries 1 and 2). The oxidation of dodecan-2-ol was repeated eight times with the

Helvetica Chimica Acta Vol. 85 (2002)
3229
same batch of recovered catalyst, and no decrease in yield or increase in reaction time
was observed. The secondary-alcohol moiety was preferentially oxidized in 2,2,4-
trimethylpentane-1,3-diol (Entry 3). This selectivity for secondary alcohols comple-
ments available methods such as TEMPO and TPAP that oxidize primary alcohols
preferentially [50]. Primary alcohols were converted to the corresponding aldehydes
after longer reaction times, without formation of other common oxidation products
such as carboxylic acids. The faster rate of secondary-alcohol oxidation is consistent
with a rate determining oxidation of a metalloester intermediate. Isolated alkenes were
not oxidized under these conditions, as shown by Entry 5. This chemoselectivity in the
presence of DMSO is advantageous, since alkene oxidation frequently competes with
alcohol oxidation in catalytic metal/peroxide systems. The oxidation of (À)-menthol
gave an isolated product that consisted of a 2 :1 mixture of menthone/isomenthone in
75% yield. This result indicates that partial epimerization at the stereogenic a-center
occurred. The epimerization can be attributed to the Lewis acidity of the ReV/VII
complexes involved in the catalytic cycle. The secondary-alcohol functions of the
steroids dihydrocholesterol and b-estradiol were oxidized to the corresponding ketones
in excellent yields (Entries 7 and 8).
A series of benzylic alcohols and cinnamyl alcohol were oxidized under the same
reaction conditions, and the results are shown in Table 2. Benzyl alcohol was oxidized
more rapidly than primary aliphatic alcohols, and benzaldehyde was isolated in 90%
yield (Entry 1). Small amounts of dibenzyl ether were also isolated from this substrate.
The 4-nitro derivative was oxidized completely to the corresponding aldehyde
(Entry 2). Benzoin (1,2-diphenyl-2-hydroxyethanone) was rapidly oxidized to benzil
(diphenylethanedione) in excellent yield (Entry 5). The oxidation of the secondary
benzylic alcohol benzhydrol (diphenylmethanol) produced only 19% of the expected
ketone and was accompanied by formation of the corresponding ether as the major
reaction product (Entry 3). The oxidation of 1,2-diphenylethanol similarly produced
only 17% of the ketone, and stilbene was isolated as the major product from a
competing elimination reaction (Entry 4). These results can be attributed to the
mildly acidic conditions of the oxidation, which can initiate the generation of
benzylic carbocations and lead to ether formation or elimination to alkene products.
This explanation is consistent with the absence of ether products in the reac-
tions of benzylic alcohols possessing electron-withdrawing groups that would desta-
bilize the intermediate cation (Entries 2 and 5). The oxidation of cinnamyl alcohol
produced the aldehyde in 36% yield (Entry 6). Small amounts of the ketone
produced from the rearranged secondary allylic alcohol and large amounts of
ether products were also formed. These observations can be explained by side
reactions of allylic alcohols under acidic conditions, where allyl cations are possible
intermediates.
Epoxide Reduction. The successful oxidation of alcohols with the polystyrene-
supported oxorhenium catalyst 2 and DMSO led us to investigate the possibility of
catalyzing other synthetically useful O-atom-transfer reactions. The reduction of
epoxides is an important reaction, and a variety of reagents have been developed [51].
The O-transfer reaction of an epoxide to triphenylphosphine is enthalpically very
favorable [52]; however, direct reaction does not occur in the absence of a catalyst such
as methyltrioxorhenium [53].

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Helvetica Chimica Acta Vol. 85 (2002)
Table 1. (Polystyrene-Catecholato)rhenium-Promoted Oxidation of Alkyl Alcohols with DMSOa)
Entry
1
Substrate
Time [h]
15
Product
Yield [%]
98
2
3
4
3.5
0.5
15
98
83
82
5
6
4
8
93
75
7
8
7
4
97
98
a) Alcohol (1 mmol), DMSO (1.5 mmol), Re-catalyst 2 (0.05 mmol), toluene (5 ml), D.
The series of epoxides (oxiranes) shown in Table 3 were reduced to the
corresponding alkenes with 1 equiv. of Ph3P and 5% of catalyst 2 in refluxing toluene.
The yields were good to excellent, and the reactions proceeded to completion without
requiring the exclusion of O2. Control experiments demonstrated that no deoxygena-
tion of trans-stilbene oxide (trans-1,2-diphenyloxirane) by Ph3P occurred after refluxing

Helvetica Chimica Acta Vol. 85 (2002)
3231
Table 2. (Polystyrene-Catecholato)rhenium-Promoted Oxidation of Benzylic and Allylic Alcohols with
DMSOa)
Entry
1
Substrate
Time [h]
2
Product(s)
Yield [%]
90
2
3
3.5
0.5
99
19
77
17
4
1.5
82
93
5
6
0.5
1
36
5
36
18
a) Alcohol (1 mmol), DMSO (1.5 mmol), Re-catalyst 2 (0.05 mmol), toluene (5 ml), D.
for 24 h in the absence of 2. Phenyloxiranes reacted more rapidly than alkyloxiranes
(Entries 1 3). Similar reaction times were required for complete conversion of cis- and
trans-stilbene oxide. The deoxygenation of trans-stilbene oxide produced (E)-stilbene
in 92% yield, with complete retention of configuration, while cis-stilbene oxide
produced a 3 :1 mixture of the (Z)/(E)-stilbene stereoisomers. A control reaction in
which (Z)-stilbene was subjected independently to the reaction conditions demon-

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Helvetica Chimica Acta Vol. 85 (2002)
strated that none of the (E)-stereoisomer was produced, which indicates that the
(Z) ! (E) isomerization occurs during the deoxygenation process. The deoxygenation
of trans-stilbene oxide was conducted repeatedly with the recovered catalyst, and no
decrease in yield or increase in reaction time was observed. The reduction of a cis-
dialkyloxirane produced the (Z)-alkene with retention of configuration (Entry 5). The
terminal epoxide 1,2-epoxyoctadecane (hexadecyloxirane) was completely deoxygen-
ated within 6 h (Entry 4). The reaction of 4-chlorophenyl glycidyl ether ([(4-
chlorophenoxy)methyl]oxirane) was significantly slower (Entry 6), and the alkene
product was isolated in moderate yield. Polycyclic di- and trisubstituted aliphatic
oxiranes were efficiently deoxygenated with this procedure (Entries 7 9). Our method
is efficient and does not require excess phosphine for complete conversion. Product
purification requires only the removal of triphenylphosphine oxide, which can be
accomplished by filtration over a small amount of silica gel.
A possible mechanism for the Re-catalyzed epoxide deoxygenation is shown in
Scheme 3. The cycle begins by coordination of an epoxide 3 to form a [ReV(catechol-
ato)] complex 4a. This species then undergoes CÀO epoxide-bond cleavage to produce
the dialkoxyrhenium(V) (glycolato)(rhenium)complex 4b. Precedence for this step has
been established in previous studies of the deoxygenation of epoxides with
methyltrioxorhenium and related cyclopentadienyl and tri(pyrazolyl)borate deriva-
tives [53 55] and in the stereospecific catalytic deoxygenation of diols to alkenes with
[Re(Cp*)(O)3] and Ph3P [56]. Alkene extrusion from 4b would produce the
[ReVII(O)2] complex 1. Alternatively, the epoxide complex 4a could undergo a direct
abstraction of the O-atom to produce 1. Reduction of the (catecholato)dioxorhe-
nium(VII) complex 1 with triphenylphosphine would then produce the ReV complex
and resume the cycle. A phenyl substituent (R ˆ C6H5) would be expected to facilitate
both of the CÀO bond-breaking steps, leading to the observed rate enhancement for
phenyloxiranes. The isomerization observed with cis-stilbene oxide might occur during
either the CÀO bond-breaking step that produces the glycolato complex, or during the
subsequent extrusion of the alkene. This isomerization may result from an asynchro-
nous CÀO bond-breaking process that involves cationic or radical intermediates
capable of rotating around the CÀC bond. These steps would be analogous to the acid-
mediated side reactions observed during the oxidation of benzylic and allylic alcohols.
The extrusion of alkenes from related [Re(Cp*)(1,2-diphenylethane-1,2-diolato)(O)]
complexes has been suggested to involve nonsymmetric transition states and stepwise
cleavage of the CÀO bonds, possibly involving a metallaoxetane intermediate [57].
The retention of confguration observed in the deoxygenation of the cis-dialkyloxirane
(Entry 5) is consistent with a synchronous process that does not involve intermediates
with free rotation around the CÀC bond. The faster rate of reaction for the simple
monoalkyloxirane (Entry 4) compared to the glycidyl derivative (Entry 6) may reflect
the ability of the additional O-atom to coordinate the metal, or alternatively this group
may play a role in the destabilization of the CÀO bond-breaking process through
inductive effects. Further investigations using isolated catecholato complexes to
elucidate mechanistic details of this reaction are currently in progress.
Conclusions. In summary, we have successfully developed a polymer-supported
rhenium catalyst for alcohol oxidation and epoxide deoxygenation. The carboxypoly-

Helvetica Chimica Acta Vol. 85 (2002)
3233
Table 3. (Polystyrene-Catecholato)rhenium-Promoted Epoxide Reduction with Ph3Pa)
Entry
1
Substrate
Time [h]
Product
Yield [%]
92
1.5
2
1.5
90
3
4
4
6
92
97
5
6
10
16
91
60
7
8
8
8
92
82
9
7
90
a) Epoxide (1 mmol), Ph3P (1 mmol), Re-catalyst 2 (0.05 mmol), toluene (5 ml), D.
styrene-supported tyramine derivative was easily synthesized and proved to be an
effective heterogeneous ligand for the formation of stable (catecholato)rhenium
complexes. The supported [Re(catecholato)] catalyst 2 was air- and moisture-stable
and could be recovered and used repeatedly without loss of activity. The alcohol
oxidation procedure uses DMSO, which is inexpensive and safer for transport and
storage than commonly used peroxide reagents. This oxidation procedure was best
suited for aliphatic alcohols, and the mild conditions were compatible with unprotected
functional groups found in alkenes, phenols, nitro compounds, and ketones. Selective

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Helvetica Chimica Acta Vol. 85 (2002)
Scheme 3
oxidation of secondary alcohols in the presence of primary alcohols was possible, and
with longer reaction time, primary alcohols were converted to aldehydes without
overoxidation. Epoxides were catalytically deoxygenated to alkenes with catalyst 2 and
Ph3P. Alkyloxiranes were converted to the alkenes with retention of configuration,
while partial isomerization was observed with cis-stilbene oxide. The workup and
purification procedures of these heterogeneous Re-catalyst-promoted transformations
involve simple filtration, and the catalyst could be recovered and used repeatedly
without loss of activity. These studies indicate that supported [Re(catecholato)]
complexes are effective catalysts for O-atom-transfer reactions and are, thus, well-
suited in organic synthesis.
Experimental Part
General. Reagent chemicals were used as obtained commercially without further purification. Carboxy-
polystyrene HL (100 200 mesh, 1% DVB; substitution: 1.24 mmol/g) and PyBOP were purchased from
Novabiochem. Alcohol and epoxide substrates, reagents, and deuterated solvents were purchased from Aldrich,
toluene and CH2Cl2 from Fischer, and potassium perrhenate from Johnson-Matthey. The starting complex
[ReCl3(O)(PPh3)2] was prepared following the literature procedure [58]. Column chromatography (CC): silica
gel 60, 70 230mesh, from Aldrich. GC: Varian 3700, Cyclodexb column (length 30 m, i.d. 0.25 mm, 0.25 mm);
samples as hexane solns. IR Spectra: Perkin-Elmer 1720X FTIR; KBr pellets; in cmÀ1. NMR Spectra: Varian
Gemini-200-Fourier-transform spectrometer; at r.t. (18 228) in CDCl3; 1H spectra referenced to SiMe4; 13C{1H}
spectra (at 50MHz) to the known solvent signals; d in ppm, coupling constants J in Hz.
Polymer-Supported Catechol. To a suspension of carboxypolystyrene HL (500 mg, 0.62 mmol) in CH2Cl2
(100 ml) was added PyBOP (967.8 mg, 1.86 mmol), followed by 3-hydroxytyramine hydrochloride (587.9 mg,
3.1 mmol) and EtNiPr2 (1.20g, 9.28 mmol). The mixture was stirred for 72 h at r.t. The mixture was filtered, and
the solid was washed sequentially with three portions each of H2O, MeOH, and CH2Cl2. The solid was dried in
vacuo: polystyrene-CONHCH2CH2C6H3(OH)2 (ˆ4-{2-{[(polystyrene)carbonyl]amino}ethyl}benzene-1,2-diol;
580mg). IR: 1604.
Polymer-Supported Rhenium Catalyst 2. To a suspension of polystyrene-CONHCH2CH2C6H3(OH)2
(500 mg) in toluene (250 ml), [ReCl3(O)(PPh3)2] (833 mg, 1 mmol) was added, followed by anh. DMSO
(425 ml, 6 mmol). The mixture was heated under reflux for 1 h. The solid was filtered, washed with three portions
of CH2Cl2, and then dried in vacuo: 715 mg of 1. IR: 1604, 908.

Helvetica Chimica Acta Vol. 85 (2002)
3235
A mixture of complex 1 (390mg), propan-2-ol (1 ml), and toluene (20ml) was heated under reflux for 1 h.
The solid was filtered, washed with three portions of CH2Cl2, and dried in vacuo: 350mg of 2. IR: 1604, 908.
Alcohol Oxidation: General Procedure. The alcohol substrate (1 mmol), catalyst 2 (94 mg, ca. 0.05 mmol of
Re), DMSO (110 ml, 1.5 mmol), and toluene (5 ml) were heated under reflux in a flask equipped with a Dean-
Stark apparatus. The progress of the reaction was monitored by TLC, and heating was continued for the time
specified in Tables 1 and 2. The mixture was cooled to r.t. and the catalyst removed by filtration and washed with
three portions of CH2Cl2. The org. layer was washed with H2O, dried (Na2SO4), and evaporated. Products were
identified by comparison of 1H- and 13C{1H}-NMR spectra with authentic material.
Deoxygenation of Epoxides: General Procedure. The epoxide substrate (1 mmol), Ph3P (1 mmol), and
catalyst 2 (94 mg, ca. 0.05 mmol of Re) in toluene (5 ml) were heated to reflux. The progress of the reaction was
monitored by TLC or GC, and heating was continued for the time described in Table 3. The mixture was cooled
to r.t. and the catalyst was removed by filtration and washed with three portions of CH2Cl2. The org. layer was
concentrated and the residue purified by CC (SiO2 ; AcOEt/hexane 1:9). Products were identified by
comparison of 1H- and 13C{1H}-NMR spectra with authentic material.
The authors thank USAMRC DAMD17-97-1-7120 and NIH GM 08136 for support of this work.
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Received June 3, 2002