Synthesis of Oxazolidinones from Epoxides and Isocyanates Catalysed by Aluminium Heteroscorpionate Complexes

Article abstract of DOI:10.1002/cctc.201600407

The combination of an aluminium(heteroscorpionate) complex and tetrabutylammonium bromide acts as a highly efficient catalyst system for the synthesis of oxazolidinones from epoxides and isocyanates. Twenty two complexes were tested derived from a range o

Full text of DOI:10.1002/cctc.201600407

DOI: 10.1002/cctc.201600407
Full Papers
Synthesis of Oxazolidinones from Epoxides and
Isocyanates Catalysed by Aluminium Heteroscorpionate
Complexes
JosØ A. Castro-Osma,*[a] Amy Earlam,[b] Agustín Lara-Sµnchez,*[c] Antonio Otero,[c] and
Michael North*[b]
The combination of an aluminium(heteroscorpionate) complex
and tetrabutylammonium bromide acts as a highly efficient
catalyst system for the synthesis of oxazolidinones from epox-
ides and isocyanates. Twenty two complexes were tested de-
rived from a range of bispyrazole ligands and containing 1–3
aluminium atoms per complex. The optimal catalyst was found
to be a bimetallic complex of a thioacetamidate ligand. Under
the optimal reaction conditions (808C in toluene for 24 h using
5 mol% of both aluminium catalyst and tetrabutylammonium
bromide co-catalyst), six epoxides were reacted with six aro-
matic isocyanates, giving 25 oxazolidinones in moderate to ex-
cellent yields showing broad substrate scope. The regiochemis-
try of the reaction (to produce 3,4- or 3,5-oxazolidinones) is
controlled by the substrate with epoxide ring opening occur-
ring preferentially at the less hindered end of the epoxide
unless a substituent on the epoxide can stabilise a positive
charge.
Introduction
Epoxides 1 are particularly useful substrates in organic synthe-
sis as many are commercially available and a number of proce-
dures have been developed for the production of enantiomeri-
cally pure epoxides.[1] They have been widely used as building
blocks for the synthesis of either cyclic or polycarbonates 2,
3,[2] cyclic dithiocarbonates 4 and trithiocarbonates 5,[3] and ox-
azolidinones 6 and 7[4] by reaction with carbon dioxide, carbon
disulfide and isocyanates, respectively (Scheme 1).
Oxazolidinones find important applications in medicinal
chemistry,[5] as chemical intermediates[6] and as chiral auxilia-
ries.[7] Many catalysts have been reported for the synthesis of
oxazolidinones from epoxides and isocyanates since Speranza
Scheme 1. Synthesis of five-membered heterocycles by the reaction
between epoxides and heterocumulenes.
[a] Dr. J. A. Castro-Osma
Departamento de Química Inorgµnica
Orgµnica y Bioquímica–Centro de Innovación en Química Avanzada
(ORFEO–CINQA)
and Peppel published the first work in 1958;[4a] including am-
monium salts, lanthanide salts, lithium halides, magnesium hal-
ides, tetraphenylantimony iodide, trialkyltin halides and metal
complexes.[4] An important aspect of the reaction is its regio-
selectivity, which determines the 6:7 ratio.
We have previously reported that bimetallic aluminium-
(salen) complex 8 (Figure 1) is an active catalyst for the reac-
tion of epoxides with carbon dioxide,[4t,8] carbon disulfide[3q,r,4t]
and isocyanates.[4q,t] For the synthesis of oxazolidinones, the
optimal conditions were 5 mol% of catalyst at 808C for 24 h in
a non-polar solvent such as toluene. The catalyst was shown
to be active for a range of mono- and disubstituted epoxides
with aromatic isocyanates, giving good to excellent yields of
oxazolidinones. Vanadium(salen) complex 9 in combination
with tetrabutylammonium bromide was also shown to be an
Universidad de Castilla–La Mancha
Instituto Regional de Investigación Científica Aplicada-IRICA, 13071-Ciudad
Real (Spain)
E-mail: JoseAntonio.Castro@uclm.es
[b] A. Earlam, Prof. M. North
Green Chemistry Centre of Excellence, Department of Chemistry
The University of York
Heslington, York, YO10 5DD (UK)
E-mail: Michael.North@york.ac.uk
[c] Dr. A. Lara-Sµnchez, Prof. A. Otero
Departamento de Química Inorgµnica
Orgµnica y Bioquímica–Centro de Innovación en Química Avanzada
(ORFEO–CINQA)
Universidad de Castilla–La Mancha
Facultad de Ciencias y Tecnologías Químicas, 13071-Ciudad Real (Spain)
E-mail: Agustin.Lara@uclm.es
Supporting Information for this article can be found under http://
dx.doi.org/10.1002/cctc.201600407.
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Table 1. Optimisation of reaction conditions for the reaction of styrene
oxide 1a with phenylisocyanate 11 a catalysed by complex 10.
Entry
10
[mol%]
Bu4NBr
[mol%]
Solvent
T
[8C]
Conv.
[%][a]
6a:7a[a]
1
2
3
4
5
6
7
8
5
5
5
5
5
–
5
10
5
5
5
5
5
5
5
5
5
5
5
5
5
–
5
5
10
5
5
5
5
5
5
5
5
5
–
–
–
25
50
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
5
16
0
100
20
25
60
62
9
40
26
14
0
41
44
45
28
1:1.4
1:1.8
–
1:1.3
1:3.0
1:3.8
1:1.7
1:1.6
0:1
1:1.3
1:3.1
1:1.8
–
1:1.5
1:1.5
1:1.2
1:1.6
toluene
toluene
toluene
DMC[b]
DMC[b]
DEC[c]
EC[d]
9
10
11
12
13
14[f]
15[g]
16[f]
17[g]
PC[e]
EtOAc
p-cymene
EC[d]
Figure 1. Catalysts for oxazolidinone and cyclic carbonate synthesis.
EC[d]
PC[e]
PC[e]
effective catalyst for the synthesis of oxazolidinones from ep-
oxides and aromatic isocyanates.[4s] This catalyst also showed
a broad scope and was applied to eight epoxides and six aro-
matic isocyanates giving the oxazolidinone products in yields
of up to 89% of the major regioisomer.
[a] Conversion of epoxide 1a into 6a+7a and ratio of 6a:7a determined
by 1H NMR spectroscopy of the unpurified reaction mixture. [b] Dimethyl
carbonate. [c] Diethyl carbonate. [d] Ethylene carbonate. [e] Propylene
carbonate. [f] 1.2 equivalents of phenylisocyanate used. [g] 3.0 equivalents
of phenylisocyanate used.
Whilst salen complexes often give active catalysts in reac-
tions involving ring opening of epoxides,[9] the tetradentate
nature of the salen ligand restricts the opportunities to vary
the coordination number and geometry around the metal
ion(s). Therefore, we have been interested in exploring the use
of other types of ligand to allow a wider range of metal com-
plex geometries to be investigated. Recently, we reported
cyclic carbonate synthesis from epoxides and carbon dioxide
using aluminium heteroscorpionate complexes as catalysts.[10]
A combination of trimetallic complex 10 and tetrabutylammo-
nium bromide was shown to be the third most active alumini-
um catalyst for the synthesis of cyclic carbonates from epox-
ides and carbon dioxide at ambient temperature and one bar
carbon dioxide pressure.[10b] Herein, we report the use of
a range of mono-, bi- and trimetallic scorpionate-based alumi-
nium complexes as catalysts for the production of oxazolidi-
nones from epoxides and isocyanates.
shown in Table 1. Initial conditions were based on the use of
5 mol% of complex 10 and tetrabutylammonium bromide as
a co-catalyst for 24 h under solvent-free conditions, which
were optimal for the reaction of carbon dioxide and epoxi-
des.[10b] However, conversions were very low for reactions per-
formed at 25–808C (Table 1, entries 1–3) because of the solidifi-
cation of the reaction mixture within two hours. This suggest-
ed that a solvent was required to increase the conversion to
the oxazolidinone products.
Toluene was initially selected as a solvent for the reaction as
it has previously been shown to be a suitable solvent for oxa-
zolidinone synthesis.[4q,t] The use of toluene had a beneficial
effect on the reaction, enabling quantitative conversion of sty-
rene oxide into a 1:1.3 ratio of oxazolidinones 6a and 7a in
24 h when 5 mol% of both complex 10 and tetrabutylammoni-
um bromide were used as the catalyst system (Table 1,
entry 4). Control experiments showed that under these condi-
tions, complex 10 or tetrabutylammonium bromide alone had
only low catalytic activity, giving 20% and 25% conversion
into oxazolidinones 6a and 7a with a ratio of 1:3.0 and 1:3.8,
respectively (entries 5,6). This suggests that a nucleophile is
needed to ring-open the epoxide coordinated to an aluminium
of complex 10.
A range of greener solvents was also investigated (Table 1,
entries 7–13), but none could match the conversion obtained
using toluene as solvent. Dimethyl (DMC) and diethyl carbon-
ate (DEC) have previously been used as green replacements
for toluene.[11] However, whilst DMC gave promising results
(entry 7), the conversion was still lower than that obtained in
toluene and could not be improved by doubling the catalyst
concentrations (entry 8). Ethylene (EC) and propylene carbon-
ate (PC) are hygroscopic and are polar aprotic solvents[12] and
Results and Discussion
For initial studies on the reaction between epoxides and iso-
cyanates, styrene oxide 1a and phenylisocyanate 11 a were
used as test substrates in a 1:1 ratio (Scheme 2). Complex 10
was as the lead catalyst as it was the most active aluminium
scorpionate catalyst for the synthesis of cyclic carbonates from
epoxides and carbon dioxide[10b] and the results obtained are
Scheme 2. Reaction of styrene oxide 1a and phenylisocyanate 11 a.
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they, like DMC, gave moderate conversions (entries 10,11).
Thus, the amount of phenylisocyanate used was increased to
1.2 or 3.0 equivalents relative to styrene oxide to investigate if
the low conversions were caused by hydrolysis of the phenyli-
socyanate. However, no significant increase in conversion was
observed (entries 14–17). Therefore, toluene was used for
further studies.
4) complexes 27–29: Binuclear alkyl aluminium complexes
containing one scorpionate ligand.[15]
5) complexes 30–32: Trinuclear alkyl aluminium complexes
containing one scorpionate ligand.[15]
Complexes 12–32 were tested for the reaction of styrene
oxide 1a with phenylisocyanate 11 a to produce oxazolidi-
nones 6a:7a in toluene at 808C for 24 h using 5 mol% of com-
plexes 12–32 and tetrabutylammonium bromide. The results
are shown in Table 2.
The structure of the catalyst was next varied and 21 addi-
tional complexes were tested (Figure 2), including:
1) complexes 12–18: Mononuclear alkyl aluminium complexes
supported by one scorpionate ligand.[13]
Table 2. Use of complexes 12–32 as catalysts for the synthesis of oxazoli-
dinones 6a:7a.[a]
2) complexes 19–20: Mononuclear phenoxide aluminium
complexes supported by one scorpionate ligand.[13]
3) complexes 21–26: Mononuclear alkyl aluminium complexes
containing two scorpionate ligands.[14]
Entry
Catalyst
Conversion
[%][b]
6a:7a
1
2
3
4
5
6
7
8
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
0
14
22
36
24
0
31
56
0
–
1:2.0
1:1.8
1:1.3
1:3.3
–
2.2:1
1:1.2
–
–
4:1
2.6:1
1.6:1
–
9
10
11
12
13
14
15
16
17
18
19
20
21
0
18
22
77
0
0
–
52
100
0
16
36
72
1:1.3
1:1.5
–
1:10
1:1.4
1:1.2
[a] Reactions performed at 808C for 24 h with 5 mol% of catalyst 12–32
and 5 mol% of tetrabutylammonium bromide. [b] Conversion of epoxide
1a into 6a+7a and ratio of 6a:7a determined by 1H NMR spectroscopy
of the unpurified reaction mixture.
Mononuclear acetamidate complexes 13–17 displayed mod-
erate levels of catalytic activity under the optimal reaction con-
ditions (Table 2, entries 2–6). In contrast, mononuclear thioace-
tamidate complex 12 displayed no catalytic activity at all
(entry 1), suggesting higher Lewis acidity of aluminium in com-
plexes 13–17 than in complex 12, probably because of the
more electron-withdrawing effect of acetamidate than thio-
acetamidate ligands. The effect of the alkyl ligand attached to
aluminium was investigated (entries 2–4) and it was found that
Me> Et> tBu, a trend that is consistent with the decrease in
the lability of the AlÀC bond. By replacing the methyl group
on the pyrazole ring by a tert-butyl group, the conversion in-
creased from 14% to 31% (entries 2 and 7), showing that en-
cumbered substituents on the pyrazoles improves the catalytic
performance. Complex 18 also changed the regiochemistry of
the oxazolidinone synthesis, favouring the formation of the
3,5-isomer 6a (entry 7). Changing the alkyl groups in complex
16 to phenoxy groups in complex 19 had a beneficial effect
on the catalytic activity of the complex (entries 5 and 8).
Figure 2. Complexes 12–32.
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Monoaluminium complexes 21–26 supported by two biden-
tate bispyrazole ligands displayed no to good catalytic activity
(Table 2, entries 10–15). In general, these complexes showed
lower catalytic activity, probably because the metal centre is
too sterically hindered by the two scorpionate ligands. The
complexes in this class that were active (22–24) also showed
inverted regiochemistry, favouring the formation of 3,5-isomer
6a (entries 11–13).
Bimetallic complex 28 showed excellent catalytic activity,
giving complete conversion of styrene oxide 1a into oxazolidi-
nones 6a:7a under optimal reaction conditions (Table 2,
entry 17) highlighting the importance of a second aluminium.
This finding was confirmed when comparing the results ob-
tained for complexes 13 and 27 (entries 2 and 16). However,
the nature of the substituent on the nitrogen of the thioaceta-
midate was critical as changing the phenyl group to a naphthyl
group resulted in dramatic decrease in catalytic activity
(entry 18). Finally, trimetallic complexes 30–32 showed moder-
ate to good catalytic activity for the synthesis of oxazolidi-
nones 6a:7a (entries 19–21). However, these complexes were
not as active as trimetallic complex 10, which gave 100% con-
version of styrene oxide 1a into 6a:7a.
The results obtained with catalysts 10, 12–32 cannot be ex-
plained just on the basis of the number of aluminium centres
in the catalysts. Thus, the two most active catalysts (10 and
28) are trimetallic and bimetallic, respectively. Complexes 27
and 10 also differ only by the presence of a third aluminium in
complex 10, yet this doubles the catalytic activity. Rather, the
results suggest that the three-dimensional orientation of two
or more Lewis acidic aluminium centres is important for opti-
mal activity, a result which is indicative of cooperative catalysis
involving two aluminium centres activating both components
of the reaction. Most of catalysts 10, 12–32 had no significant
effect on the regiochemistry of the reaction, exhibiting a slight
preference for the formation of 3,4-isomer 7a. However, steri-
cally hindered mononuclear complexes 18 and 22–24 did have
an effect on the reaction regiochemistry, giving 3,5-isomer 6a
as the major product, though with very low conversions
except for complex 24, which unfortunately gave the lowest
regioselectivity (entry 13).
Scheme 3. Synthesis of oxazolidinones 6a–s/7a–s.
sion, with the 3,5-isomer 7d as the major product (entry 4).
Glycidol 1e was found not to be a good substrate for this re-
action because the alcohol functionality can react with the
alkyl groups and hydrolyse catalyst 28 (entry 5). In contrast,
functionalised aliphatic epoxides epichlorohydrin 1 f and 3-
phenoxypropylene oxide 1g were excellent substrates, giving
100% conversion and 100% regioselectivity to the 3,5-isomer
6 f–g (entries 6,7). These results are consistent with the nucleo-
philic attack of the bromide taking place at the less hindered
carbon atom of an aliphatic epoxide by an SN2 type mecha-
nism, but in some cases, also at the more hindered carbon
atom by a mechanism with some SN1 character. Relative to 1-
decene oxide 1d with a simple alkyl substituent, the presence
of electronegative groups (as in epoxides 1 f and 1g) disfa-
vours the SN1 type reaction, whilst aromatic groups favour the
SN1 type process to an extent that depends on how electron-
rich the aromatic ring is (epoxides 1a–c).[16]
Styrene oxide 1a and epichlorohydrin 1 f were selected as
representative aromatic and aliphatic epoxides respectively for
the synthesis of a wider range of oxazolidinones. These epox-
ides were reacted with five substituted aromatic isocyanates
11 b–f and two aliphatic isocyanates 11 g,h and the results are
shown in Table 3, entries 8–21. Catalyst 28 was found to be
highly active for the synthesis of oxazolidinones if aromatic iso-
cyanates 11 b–f were used, achieving good to excellent con-
versions and isolated yields (entries 8–12 and 15–19). However,
no conversion was obtained if aliphatic isocyanates 11 g,h
were used (entries 13,14 and 20,21), indicating that the reac-
Amongst the aluminium catalysts studied, catalysts 10 and
28 gave quantitative conversions to the oxazolidinone pro-
ducts 6a:7a in a 1:1.3 and 1:1.5, ratio respectively. As com-
plex 28 gave a slightly higher 6a:7a ratio, is more stable and
easier to synthesise, we determined that complex 28 was the
optimal catalyst for this transformation. Therefore, we investi-
gated the synthesis of a range of oxazolidinones using 5 mol%
of catalyst 28 and 5 mol% of tetrabutylammonium bromide in
toluene at 808C for 24 h (Scheme 3) and the results are shown
in Table 3.
If aromatic epoxides 1b and 1c containing an electron-with-
drawing group in the para-position were used as substrates
(Table 3, entries 2,3), excellent conversions were achieved
though the 6b,c:7b,c ratio decreased from 1:1.5 to 1:1. This is
caused by the electron-withdrawing groups destabilizing the
benzylic carbocation favouring the formation of the 3,4-isomer
6b,c. Unfunctionalised aliphatic epoxide 1d gave 85% conver-
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Table 3. Synthesis of oxazolidinones 6a–s/7a–s catalysed by complex 28.[a]
Entry
Epoxide
Isocyanate
Conv.
[%][b]
Yield
[%][c]
6a:7a
1
2
3
4
5
6
7
8
1a (R1 =Ph)
11 a (R2 =Ph)
100
100
100
85
96
75
73
67
1:1.5
1:1
1:1
3.2:1
–
1:0
1:0
1:1.2
1:1.3
1:1.4
1:1.4
1:1.3
–
1b (R1 =4-ClC6H4)
1c (R1 =4-BrC6H4)
1d (R1 =Oct)
1e (R1 =CH2OH)
1 f (R1 =CH2Cl)
1g(R1 =CH2OPh)
1a (R1 =Ph)
11 a (R2 =Ph)
11 a (R2 =Ph)
11 a (R2 =Ph)
11 a (R2 =Ph)
0
11 a (R2 =Ph)
100
100
100
100
69
91
88
0
0
71
82
100
100
100
0
97
93
79
86
62
73
65
–
11 a (R2 =Ph)
11 b (R2 =4-FC6H4)
11 c (R2 =4-ClC6H4)
11 d (R2 =4-BrC6H4)
11 e (R2 =4-MeC6H4)
11 f (R2 =4-MeOC6H4)
11 g (R2 =CH2Ph)
11 h (R2 =Et)
9
1a (R1 =Ph)
10
11
12
13
14
15
16
17
18
19
20
21
1a (R1 =Ph)
1a (R1 =Ph)
1a (R1 =Ph)
1a (R1 =Ph)
1a (R1 =Ph)
–
–
1 f (R1 =CH2Cl)
1 f (R1 =CH2Cl)
1 f (R1 =CH2Cl)
1 f (R1 =CH2Cl)
1 f (R1 =CH2Cl)
1 f (R1 =CH2Cl)
1 f (R1 =CH2Cl)
11 b (R2 =4-FC6H4)
11 c (R2 =4-ClC6H4)
11 d (R2 =4-BrC6H4)
11 e (R2 =4-MeC6H4)
11 f (R2 =4-MeOC6H4)
11 g (R2 =CH2Ph)
11 h (R2 =Et)
67
81
79
81
78
–
1:0
1:0
1:0
1:0
1:0
–
0
–
–
[a] Reactions performed at 808C for 24 h with 5 mol% of catalyst 28 and 5 mol% of tetrabutylammonium bromide. [b] Conversion of epoxide 1a–g into
1
6a–s+7a–s and ratio of 6a–s:7a–s determined by H NMR spectroscopy of the unpurified reaction mixture. [c] Yield of isolated oxazolidinone.
tion is restricted to aromatic isocyanates. As presented in
Table 3 and consistent with the analysis presented above, if
styrene oxide 1a was used as substrate and reacted with aro-
matic isocyanates, 3,4-oxazolidinones 7h–l were the major
products formed in a 1:1.2 to 1:1.4 ratio relative to the 3,5-
isomer 6h–l. However, if epichlorohydrin 1 f was reacted with
aromatic isocyanates, the reaction was completely regioselec-
tive for the formation of the 3,5-oxazolidinone products 6o–r.
Based on the need for a co-catalyst, the higher reactivity of
polymetallic complexes and previous results for the synthesis
of cyclic carbonates catalysed by acetamidate and thioacetami-
date scorpionate aluminium complexes,[10] we propose the
mechanism shown in Scheme 4. First, the epoxide is activated
by coordination to one of the aluminium centres. Then, the
bromide anion provided by the tetrabutylammonium bromide
Scheme 4. Possible mechanism for the synthesis of oxazolidinones catalysed
ring-opens the coordinated epoxide to form a halo-alkoxide.
The isocyanate can be activated by a second aluminium centre
(if present in the catalyst) and is inserted into the aluminium–
oxygen bond to afford a carbamate, which can ring-close to
give the oxazolidinone and regenerate the tetrabutylammoni-
um bromide and the aluminium complex. The formation of re-
gioisomer 6 or 7 is determined by the regiochemistry of the in-
itial epoxide ring opening by bromide, which in turn is deter-
mined by the nature of the substituent attached to the epox-
ide rather than by the nature of the catalyst except if the cata-
lyst contains only sterically hindered aluminiums.
by heteroscorpionate aluminium complexes.
minium(salen) catalyst 8, tetrabutylammonium bromide is re-
quired as a co-catalyst whilst this was shown to inhibit oxazoli-
dinone formation catalysed by complex 8.[4q] The reaction
mechanism seems to involve a dual Lewis acid activation of
the epoxide and the isocyanate by aluminium complex 28 and
a nucleophilic attack of the bromide predominantly at the less
hindered carbon atom of the epoxide.
Compared to the previously reported catalysts for this reac-
tion,[4a,c,d] the combination of complex 28 and tetrabutylammo-
nium bromide allows reactions to be conducted at lower tem-
peratures. Only 5 mol% of catalyst loading is needed to ach-
ieve good to excellent yields compared to previous catalyst
systems in which up to 50 mol% was required.[4f,h–j,p] The regio-
chemistry of the reaction is controlled by the substrate on the
Conclusions
Bimetallic scorpionate aluminium complex 28 catalyses the
synthesis of oxazolidinones from epoxides and aromatic iso-
cyanates. Compared to our previously reported bimetallic alu-
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found: 240.1015. calcd. m/z 262.0838 [C15H13NO2 +Na]+; found:
basis of carbenium ion stability rather than the catalyst as the
same regiochemical trends have been observed with previous-
ly reported metal(salen)-based catalysts[4q,s,t] and the complexes
reported in this paper. Complex 28 is derived from aluminium,
which is inexpensive and an Earth-crust abundant metal,[17]
avoiding the use of highly toxic catalysts[4f–l] and expensive lan-
thanide-based catalysts.[4u,18] The largest remaining challenge
in enhancing the sustainability of this reaction is the use of
toxic isocyanates. Future work should focus on using alterna-
tive reagents such as carbamates or on the in situ generation
of isocyanates from non-toxic precursors such as amines and
carbon dioxide.
262.0838. IR Neat: n˜ =1741.3 cmÀ1
.
3-Phenyl-5-(4-chlorophenyl)-oxazolidin-2-one (6b): Obtained as
a pale yellow solid after purification by flash chromatography
using a solvent system of CH2Cl2–hexane (4:1) (90 mg, 38%). M.p.
124–1268C. 1H NMR (400 MHz, CDCl3, 298 K): d=7.54 (2H, d, J
7.9 Hz, ArH), 7.45–7.35 (6H, m, ArH), 7.16 (1H, td, J 7.4, 0.9 Hz,
ArH), 5.64 (1H, t, J 8.2 Hz, CHO), 4.39 (1H, t, J 8.9 Hz, CH2N),
3.93 ppm (1H, dd, J 8.9, 7.5 Hz, CH2N). 13C{1H}-NMR (100 MHz,
CDCl3, 298 K): d=154.4, 137.9, 136.6, 135.1, 129.3, 129.1, 127.1,
124.3, 118.3, 73.3, 52.6 ppm. Mass spec. (ESI+): calcd. m/z 274.0629
[C15H12ClNO2 +H]+; found: 274.0636. Calcd. m/z 296.0449
[C15H12ClNO2 +Na]+; found: 296.0449. IR Neat: n˜ =1733.4 cmÀ1
.
3-Phenyl-4-(4-chlorophenyl)-oxazolidin-2-one (7b): Obtained as
a pale yellow solid after purification by flash chromatography
using a solvent system of CH2Cl2–hexane (4:1) (90 mg, 38%). M.p.
Experimental Section
1
140–1428C. H NMR (400 MHz, CDCl3, 298 K): d=7.40–7.20 (8H, m,
Commercially available chemicals (Alfa, Aldrich, Fluka) were used
as received and all reactions were performed in dry glassware. Het-
eroscorpionate ligands and aluminium complexes 10 and 12--32
were prepared as reported previously.[13–15] 1H and 13C NMR spectra
were recorded on a Jeol Oxford 400 spectrometer at resonance fre-
quencies of 400 and 100 MHz, respectively. All spectra were record-
ed at ambient temperature and were referenced to the residual
solvent peak. Mass spectrometry was performed by the University
of York mass spectrometry service using electrospray ionisation
(ESI). Melting points were determined using a Stuart SMP3 appara-
tus. Infrared spectra were recorded on a Bruker Vertex 70 instru-
ment equipped with “Specac” Golden Gate Single Reflection
Diamond ATR accessories.
ArH), 7.12–7.02 (1H, m, ArH), 5.37 (1H, dd, J 8.7, 6.0 Hz, CHN), 4.76
(1H, dd, J 9.3 8.2 Hz, CH2O), 4.15 ppm (1H, dd, J 8.7, 6.0 Hz, CH2O).
13C{1H}-NMR (100 MHz, CDCl3, 298 K): d=155.8, 136.8, 136.8, 134.9,
129.7, 129.1, 127.7, 125.0, 120.9, 69.6, 60.2 ppm. Mass spec. (ESI+):
calcd. m/z 274.0629 [C15H12ClNO2 +H]+; found: 274.0636. Calcd.
m/z 296.0449 [C15H12ClNO2 +Na]+; found: 296.0449. IR Neat: n˜ =
1733.4 cmÀ1
.
3-Phenyl-5-(4-bromophenyl)-oxazolidin-2-one (6c): Obtained as
a white solid after purification by flash chromatography using a sol-
vent system of first hexane–EtOAc (7:1), then hexane–EtOAc (4:1),
1
then hexane–EtOAc (3:1), (100 mg, 36%). M.p 132–1348C. H NMR
(400 MHz, CDCl3, 298 K): d=7.60–7.50 (4H, m, ArH), 7.45–7.35 (2H,
m, ArH), 7.35–7.30 (2H, m, ArH), 7.20–7.10 (1H, m, ArH), 5.60 (1H, t,
J 8.2 Hz, CHO), 4.39 (1H, t, J 8.9 Hz, CH2N), 3.92 ppm (1H, dd, J 8.9,
7.5 Hz, CH2N). 13C{1H}-NMR (100 MHz, CDCl3, 298 K): d=155.4, 137.9,
137.2, 132.2, 129.2, 127.3, 124.4 123.2, 118.3, 73.3, 52.5 ppm. Mass
spec. (ESI+): calcd. m/z 339.9944 [C15H12BrNO2 +Na]+; found:
General procedure for oxazolidinone synthesis
Epoxide 1a–g (0.874 mmol) and isocyanate 11 a–h (0.874 mmol)
were added to solution of catalyst 10, 12–32 (0.044 mmol) and
Bu4NBr (14 mg, 0.044 mmol) in dry toluene (1.5 mL). The resulting
mixture was stirred at 808C for 24 h. After being allowed to cool to
RT, toluene was removed in vacuo to give the crude oxazolidinone
products. The conversion of epoxide to oxazolidinone was then de-
339.9937. IR Neat: n˜ =1725.5 cmÀ1
.
3-Phenyl-4-(4-bromophenyl)-oxazolidin-2-one (7c): Obtained as
a yellow solid after purification by flash chromatography using
a solvent system of first hexane–EtOAc (7:1), then hexane–EtOAc
(4:1), then hexane-EtOAc (3:1), (103 mg, 37%). M.p. 156–1588C.
1H NMR (400 MHz, CDCl3, 298 K): d=7.49 (2H, d, J 8.4 Hz, ArH),
7.40–7.35 (2H, m, ArH), 7.30–7.25 (2H, m, ArH), 7.19 (2H, d, J 8.4,
ArH), 7.10 (1H, t, J 7.4, ArH), 5.37 (1H, dd, J 8.7, 6.0 Hz, CHN), 4.78
(1H, t, J 8.7 Hz, CH2O), 4.17 ppm (1H, dd, J 8.7, 6.0 Hz, CH2O).
13C{1H}-NMR (100 MHz, CDCl3, 298 K): d=155.4, 136.9, 132.3, 128.9,
128.7, 127.6 124.6, 122.6, 120.5, 69.2, 59.8 ppm. Mass spec. (ESI+):
calcd. m/z 339.9944 [C15H12BrNO2 +Na]+; found: 339.9937. IR Neat:
1
termined by H NMR spectroscopy of the crude mixture. The prod-
ucts were purified by flash chromatography to give compounds 6/
7a–s.
3,5-Diphenyloxazolidin-2-one (6a): Obtained as a yellow solid
after purification by flash chromatography using a solvent system
of first hexane–EtOAc (5:1), then hexane–EtOAc (3:1). (80 mg,
38%). M.p. 80–828C (lit. 79–828C).[4q] 1H NMR (400 MHz, CDCl3,
298 K): d=7.56 (2H, d, J 7.8 Hz, ArH), 7.46–7.35 (7H, m, ArH), 7.15
(1H, t, J 7.4 Hz, ArH), 5.64 (1H, dd, J 8.6, 7.6 Hz, CHO), 4.38 (1H, t, J
8.8 Hz, CH2N), 3.96 ppm (1H, dd, J 8.9, 7.6 Hz, CH2N). 13C{1H}-NMR
(100 MHz, CDCl3, 298 K): d=154.8, 138.2, 138.2, 129.2, 129.1, 125.8,
124.3, 118.4, 74.1, 52.8 ppm. Mass spec. (ESI+): calcd. m/z 240.1019
[C15H13NO2 +H]+; found: 240.1015. calcd. m/z 262.0838
n˜ =1745.2 cmÀ1
.
3-Phenyl-5-octyloxazolidin-2-one (6d): Obtained as a white solid
after purification by flash chromatography using a solvent system
of hexane–EtOAc (9:1) (123 mg, 51%). M.p. 71–738C (lit. 70–
718C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=7.54 (2H, d, J 8.9 Hz,
ArH), 7.37 (2H, t J 8.1 Hz, ArH), 7.13 (1H, t, J 7.4 Hz, ArH), 4.64 (1H,
m, CHO), 4.08 (1H, t, J 8.5 Hz, CH2N), 3.66 (1H, dd, J 8.6, 7.2 Hz,
CH2N), 1.90–1.60 (2H, m, CH2), 1.45–1.15 (12H, m, 6”CH2), 0.95–
0.75 ppm (3H, m, CH3). 13C{1H}-NMR (100 MHz, CDCl3, 298 K): d=
155.3, 138.7, 129.3, 124.2, 118.5, 73.4, 50.8, 35.4, 32.1, 29.7, 29.6,
29.5, 24.9, 22.9, 14.4 ppm. Mass spec. (ESI+): calcd. m/z 276.1958
[C17H25NO2 +H]+; found: 276.1960. Calcd. m/z 298.1778
[C15H13NO2 +Na]+; found: 262.0838. IR Neat: n˜ =1745.2 cmÀ1
.
3,4-Diphenyloxazolidin-2-one (7a): Obtained as a yellow solid
after purification by flash chromatography using a solvent system
of first hexane–EtOAc (5:1), then hexane–EtOAc (3:1) (121 mg,
58%). M.p. 77–798C (lit. 76–788C).[4q] 1H NMR (400 MHz, CDCl3,
298 K): d=7.50–7.20 (9H, m, ArH), 7.10 (1H, t, J 7.4 Hz, ArH), 5.43
(1H, dd, J 8.7, 6.0 Hz, CHN), 4.80 (1H, t, J 8.7 Hz, CH2O), 4.23 ppm
(1H, dd, J 8.6, 6.0 Hz, CH2O). 13C{1H}-NMR (100 MHz, CDCl3, 298 K):
d=155.8, 138.6, 137.3, 129.4, 128.9, 128.8, 126.3, 124.7, 121.0, 69.8,
60.9 ppm. Mass spec. (ESI+): calcd. m/z 240.1019 [C15H13NO2 +H]+;
[C17H25NO2 +Na]+; found: 298.1771. IR Neat: n˜ =1716.6 cmÀ1
.
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Full Papers
3-Phenyl-4-octyloxazolidin-2-one (7d): Obtained as a pale yellow
oil after purification by flash chromatography using a solvent
system of hexane–EtOAc (9:1) (39 mg, 16%). 1H NMR (400 MHz,
CDCl3, 298 K): d=7.60–7.30 (3H, m, ArH), 7.25–7.15 (2H, m, ArH),
4.56 (1H, t, J 8.4 Hz, CHN), 4.50–4.35 (1H, m, CH2O), 4.16 (1H, dd, J
8.3, 5.3 Hz, CH2O), 1.85–1.45 (2H, m, CH2), 1.45–1.15 (12H, m, 6”
CH2), 0.88 ppm (3H, t, J 6.5 Hz, CH3). 13C{1H}-NMR (100 MHz, CDCl3,
298 K): d=155.7, 137.0, 129.2, 125.2, 122.1, 66.9, 56.5, 32.0, 31.7,
29.3, 29.2, 29.0, 24.0, 22.5, 13.9 ppm. Mass spec. (ESI+): calcd. m/z
276.1958 [C17H25NO2 +H]+; found: 276.1955. Calcd. m/z 298.1778
3-(4-Chlorophenyl)-5-phenyloxazolidin-2-one (6i): Obtained as
a pale yellow solid after purification by flash chromatography
using a solvent system of hexane–EtOAc (9:1) (89 mg, 37%). M.p.
115–1198C (lit. 113–1178C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=
7.55–7.25 (9H, m, ArH), 5.66 (1H, dd, J 8.5, 7.8 Hz, CHO), 4.37 (1H,
t, J 8.8 Hz, CH2N), 3.95 ppm (1H, dd, J 8.8, 7.6 Hz, CH2N). 13C{1H}-
NMR (100 MHz, CDCl3, 298 K): d=154.8, 138.1, 137.0, 129.7, 129.5,
129.4, 125.9, 119.7, 74.3, 52.9 ppm. Mass spec. (ESI+): calcd. m/z
274.0629 [C15H12ClNO2 +H]+; found: 274.0629. calcd. m/z 296.0449
[C15H12ClNO2 +Na]+; found: 296.0449. IR Neat: n˜ =1735.9 cmÀ1
.
[C17H25NO2 +Na]+; found: 298.1781. IR Neat: n˜ =1723 cmÀ1
.
3-(4-Chlorophenyl)-4-phenyloxazolidin-2-one (7i): Obtained as
a pale orange solid after purification by flash chromatography
using a solvent system of hexane–EtOAc (9:1) (116 mg, 49%). M.p.
125–128 (lit. 126–1288C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=
7.50–7.30 (9H, m, ArH), 5.36 (1H, dd, J 8.7, 6.2 Hz, CHN), 4.79 (1H,
t, J 8.7 Hz, CH2O), 4.21 ppm (1H, dd, J 8.7, 6.1 Hz, CH2O). 13C{1H}-
NMR (100 MHz, CDCl3, 298 K): d=155.7, 137.7, 135.5, 129.8, 129.4,
129.0, 128.9, 126.2, 121.8, 69.7, 60.5 ppm. Mass spec. (ESI+): calcd.
m/z 274.0629 [C15H12ClNO2 +H]+; found: 274.0629. calcd. m/z
296.0449 [C15H12ClNO2 +Na]+; found: 296.0449. IR Neat: n˜ =
3-Phenyl-5-chloromethyloxazolidin-2-one (6 f): Obtained as
a pale yellow solid after purification by flash chromatography
using a solvent system of hexane–EtOAc (2:1) (179 mg, 97%). M.p.
108–1108C (lit. 101–1038C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=
7.60–7.50 (2H, m, ArH), 7.45–7.35 (2H, m, ArH), 7.16 (1H, tt, J 7.4,
1.0 Hz, ArH), 4.95–4.80 (1H, m, CHO), 4.17 (1H, t, J 9.0, Hz, CH2N),
3.96 (1H, dd, J 9.2, 5.7 Hz, CH2N), 3.79 (1H, dd, J 11.6, 4.1 CH2Cl),
3.74 ppm (1H, dd, J 11.6, 6.5, CH2Cl). 13C{1H}-NMR (100 MHz, CDCl3,
298 K): d=153.9, 137.8, 129.1, 124.4, 118.3, 70.8, 48.1, 44.5 ppm.
Mass spec. (ESI+): calcd. m/z 234.0292 [C10H10ClNO2 +Na]+; found:
1728.2 cmÀ1
.
234.0298. IR Neat: n˜ =1727.9 cmÀ1
.
3-(4-Bromophenyl)-5-phenyloxazolidin-2-one (6j): Obtained as
a pale yellow solid after purification by flash chromatography
using a solvent system of hexane–EtOAc (9:1) (72 mg, 26%). M.p.
101–1058C (lit. 100–1038C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=
7.70–7.30 (9H, m, ArH), 5.64 (1H, t, J 8.5 Hz, CHO), 4.36 (1H, t, J
8.8 Hz, CH2N), 3.94 ppm (1H, dd, J 8.8, 7.6 Hz, CH2N). 13C{1H}-NMR
(100 MHz, CDCl3, 298 K): d=154.4, 137.9, 137.2, 132.7, 132.1, 130.0,
129.2, 129.1, 125.6, 119.7, 74.0, 52.6 ppm. Mass spec. (ESI+): calcd.
m/z 318.0124 [C15H12BrNO2 +H]+; found: 318.0125. calcd. m/z
339.9944 [C15H12BrNO2 +Na]+; found: 339.9941. IR Neat: n˜ =
3-Phenyl-5-phenoxymethyloxazolidin-2-one (6g): Obtained as
a pale yellow solid after purification by flash chromatography
using a solvent system of first hexane–EtOAc (3:1), then hexane–
EtOAc (2:1) (218 mg, 93%). M.p. 138–1418C (lit. 139–1408C).[4q]
1H NMR (400 MHz, CDCl3, 298 K): d=7.60 (2H, d, J 7.9 Hz, ArH), 7.42
(2H, t, J 8.02 Hz, ArH), 7.31 (2H, d, J 8.5 Hz, ArH), 7.18 (1H, t, J
7.4 Hz, ArH), 7.02 (1H, t, J 7.3 Hz, ArH), 6.93 (2H, d, J 7.9 Hz, ArH),
5.10–4.90 (1H, m, CHO), 4.35–4.20 (3H, m, CH2O+CH2N), 4.10 ppm
(1H, dd, J 8.9, 6.0 Hz, CH2N). 13C{1H}-NMR (100 MHz, CDCl3, 298 K):
d=158.3, 154.3, 138.4, 129.7, 129.1, 124.3, 122.0, 118.6, 115.0, 70.5,
68.4, 47.7 ppm. Mass spec. (ESI+): calcd. m/z 292.0944
1749 cmÀ1
.
3-(4-Bromophenyl)-4-phenyloxazolidin-2-one (7j): Obtained as
a pale yellow solid after purification by flash chromatography
using a solvent system of hexane–EtOAc (9:1) (101 mg, 36%). M.p.
132–1358C (lit. 134–1378C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=
7.50–7.30 (9H, m, ArH), 5.35 (1H, dd, J 8.7, 6.0 Hz, CHN), 4.77 (1H,
t, J 8.7 Hz, CH2O), 4.19 ppm (1H, dd, J 8.6, 6.0 Hz, CH2O). 13C{1H}-
NMR (100 MHz, CDCl3, 298 K): d=155.6, 137.7, 136.1, 131.9, 129.5,
129.0, 126.1, 122.1, 117.6, 69.7, 60.5 ppm. Mass spec. (ESI+): calcd.
m/z 318.0124 [C15H12BrNO2 +H]+; found: 318.0130. calcd. m/z
339.9944 [C15H12BrNO2 +Na]+; found: 339.9944. IR Neat: n˜ =
[C16H15NO3 +Na]+; found: 292.0949. IR Neat: n˜ =1731.9 cmÀ1
.
3-(4-Fluorophenyl)-5-phenyloxazolidin-2-one (6h): Obtained as
a pale yellow solid after purification by flash chromatography
using a solvent system of first hexane–EtOAc (7:1), then hexane–
EtOAc (5:1) (81 mg, 36%). M.p. 78–808C (lit. 78–818C).[4q] 1H NMR
(400 MHz, CDCl3, 298 K): d=7.55–7.40 (7H, m, ArH), 7.08 (2H, m,
ArH), 5.65 (1H, dd, J 8.6, 7.6 Hz, CHO), 4.37 (1H, t, J 8.8 Hz, CH2N),
3.95 ppm (1H, dd, J 8.6, 7.6 Hz, CH2N). 13C{1H}-NMR (100 MHz,
CDCl3, 298 K): d=159.4 (d, J 244 Hz), 154.8, 137.9, 134.2, 129.2,
129.1, 125.6, 120.1 (d, J 8 Hz), 115.8 (d, J 23 Hz), 74.0, 53.0 ppm.
19F NMR (376 MHz, CDCl3, 298 K): d=À118.25 ppm (s). Mass spec.
(ESI+): calcd. m/z 258.0925 [C15H12FNO2 +H]+; found: 280.0749.
calcd. m/z 280.0744 [C15H12FNO2 +Na]+; found: 280.0749. IR Neat:
1742 cmÀ1
.
3-(4-Methylphenyl)-5-phenyloxazolidin-2-one (6k): Obtained as
a white solid after purification by flash chromatography using a sol-
vent system of hexane–EtOAc (9:1) (68 mg, 31%). M.p. 96–988C
(lit. 98–1008C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=7.50–7.35
(6H, m, ArH), 7.18 (2H, d, J 8.4 Hz, ArH), 5.63 (1H, t, J 8.1 Hz, CHO),
4.36 (1H, t, J 8.8 Hz, CH2N), 3.94 (1H, dd, J 8.8, 7.6 Hz, CH2N),
2.34 ppm (3H, s, CH3). 13C{1H}-NMR (100 MHz, CDCl3, 298 K): d=
154.8, 138.2, 135.6, 133.9, 129.6, 129.0, 129.0, 125.7, 118.4, 74.0,
52.9, 20.7 ppm. Mass spec. (ESI+): calcd. m/z 254.1176
[C16H15NO2 +H]+; found: 254.1168. calcd. m/z 276.0995
n˜ =1732.1 cmÀ1
.
3-(4-Fluorophenyl)-4-phenyloxazolidin-2-one (7h): Obtained as
a pale yellow solid after purification by flash chromatography
using a solvent system of first hexane–EtOAc (7:1), then hexane–
EtOAc (5:1) (97 mg, 43%). M.p. 95–978C (lit. 94–978C).[4q] 1H NMR
(400 MHz, CDCl3, 298 K): d=7.4–7.25 (7H, m, ArH), 6.93 (2H, m,
ArH), 5.33 (1H, dd, J 8.8, 6.3 Hz, CHN), 4.77 (1H, t, J 8.7 Hz, CH2O),
4.20 ppm (1H, dd, J 8.7, 6.3 Hz, CH2O). 13C{1H}-NMR (100 MHz,
CDCl3, 298 K): d=161.5, 155.9, 138.2, 133.3, 129.5, 129.0, 126.4,
123.1 (d, J 8 Hz), 115.7 (d, J 23 Hz), 69.7, 61.3 ppm. 19F NMR
(376 MHz, CDCl3, 298 K): d=À117.01 ppm (s). Mass spec. (ESI+):
calcd. m/z 258.0925 [C15H12FNO2 +H]+; found: 280.0749. calcd. m/z
280.0744 [C15H12FNO2 +Na]+; found: 280.0749. IR Neat: n˜ =
[C16H15NO2 +Na]+; found: 279.0991. IR Neat: n˜ =1735 cmÀ1
.
3-(4-Methylphenyl)-4-phenyloxazolidin-2-one (7k): Obtained as
a white solid after purification by flash chromatography using a sol-
vent system of hexane–EtOAc (9:1) (95 mg, 43%). M.p. 106–1088C
(lit. 105–1078C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=7.40–7.20
(6H, m, ArH), 7.05 (2H, d, J 8.7 Hz, ArH), 5.36 (1H, dd, J 8.8, 6.2 Hz,
CHN), 4.76 (1H, t, J 8.7 Hz, CH2O), 4.25–4.15 (1H, m, CH2O),
2.25 ppm (3H, s, CH3). 13C{1H}-NMR (100 MHz, CDCl3, 298 K): d=
1732.1 cmÀ1
.
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Full Papers
156.0, 138.3, 134.5, 134.4, 129.5, 129.3, 128.7, 126.3, 121.1, 69.8,
3-(4-Methylphenyl)-5-chloromethyloxazolidin-2-one (6r): Ob-
tained as a pale yellow solid after purification by flash chromatog-
raphy using a solvent system of hexane–EtOAc (3:1) (160 mg,
81%). M.p. 104–1068C (lit. 104–1078C).[4q] 1H NMR (400 MHz, CDCl3,
298 K): d=7.42 (2H, d J 8.5 Hz), 7.18 (2H, d J 8.3 Hz), 4.95–4.77
(1H, m, CHO), 4.14 (1H, t J 9.0 Hz, CH2N), 3.93 (1H, dd, J 9.2, 5.7 Hz,
CH2N), 3.79 (1H, dd, J 11.6, 4.1 Hz, CH2Cl), 3.73 (1H, dd, J 11.6,
6.7 Hz, CH2Cl), 2.32 ppm (3H, s, CH3). 13C{1H}-NMR (100 MHz, CDCl3,
298 K): d=154.0, 135.6, 134.1, 129.6, 118.5, 70.8, 48.3, 44.5,
20.7 ppm. Mass spec. (ESI+): calcd. m/z 226.0629 [C11H12ClNO2 +
H]+; found: 226.0619. calcd. m/z 248.0449 [C11H12ClNO2 +Na]+;
60.8, 20.7 ppm. Mass spec. (ESI+): calcd. m/z 276.0995
[C16H15NO2 +Na]+; found: 279.1005. IR Neat: n˜ =1739 cmÀ1
.
3-(4-Methoxyphenyl)-5-phenyloxazolidin-2-one (6l): Obtained as
a pale orange solid after purification by flash chromatography
using a solvent system of hexane:EtOAc (5:1) (66 mg, 28%). M.p.
100–1028C (lit. 105–1078C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=
7.50–7.35 (7H, m, ArH), 6.97–6.87 (2H, m, ArH), 5.63 (1H, dd, J 8.6,
7.6 Hz, CHO), 4.35 (1H, t, J 8.8 Hz, CH2N), 3.94 (1H, dd, J 8.8, 7.6 Hz,
CH2N), 3.80 ppm (3H, s, OCH3). 13C{1H}-NMR (100 MHz, CDCl3,
298 K): d=156.4, 155.0, 138.2, 131.2, 129.0, 128.9, 125.6, 120.5,
114.2, 73.9, 55.4, 53.1 ppm. Mass spec. (ESI+): calcd. m/z 270.1125
[C16H15NO3 +H]+; found: 270.1124. calcd. m/z 292.0944
found: 248.0448. IR Neat: n˜ =1732 cmÀ1
.
3-(4-Methoxyphenyl)-5-chloromethyloxazolidin-2-one (6s): Ob-
tained as a yellow solid after purification by flash chromatography
using a solvent system of hexane–EtOAc (3:1) (165 mg, 78%). M.p.
106–1088C (lit. 105–1068C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=
7.42 (2H, d, J 9.1 Hz, ArH), 6.91 (2H, d, J 9.1 Hz, ArH), 4.9–4.8 (1H,
m, CHO), 4.12 (1H, t, J 8.9 Hz, CH2N), 3.91 (1H, dd, J 9.1, 5.7 Hz,
CH2N), 3.79 (3H, s, OCH3), 3.78–3.73 ppm (2H, m, CH2Cl). 13C{1H}-
NMR (100 MHz, CDCl3, 298 K): d=156.6, 154.2, 130.8, 120.4, 114.4,
70.8, 55.5, 48.6, 44.6 ppm. Mass spec. (ESI+): calcd. m/z 242.0578
[C11H12ClNO3 +H]+; found: 242.0575. calcd. m/z 264.0398
[C16H15ClNO2 +Na]+; found: 292.0944. IR Neat: n˜ =1732.1 cmÀ1
.
3-(4-Methoxyphenyl)-4-phenyloxazolidin-2-one (7l): Obtained as
a pale orange solid after purification by flash chromatography
using a solvent system of hexane–EtOAc (5:1) (86 mg, 37%). M.p.
134–1368C (lit. 137–1388C).[4q] 1H NMR (400 MHz, CDCl3, 298 K): d=
7.30–7.12 (7H, m, ArH), 6.74 (2H, d, J 9.2 Hz, ArH), 5.26 (1H, dd, J
8.7, 6.4 Hz, CHN), 4.72 (1H, t, J 8.7 Hz, CH2O), 4.16 (1H, dd, J 8.7,
6.4 Hz, CH2O), 3.67 ppm (3H, s, OCH3). 13C{1H}-NMR (100 MHz,
CDCl3, 298 K): d=156.8, 156.4, 138.2, 129.8, 129.2, 128.8, 126.5,
123.3, 114.2, 69.7, 61.4, 55.3 ppm. Mass spec. (ESI+): calcd. m/z
270.1125 [C16H15NO3 +H]+; found: 270.1124. calcd. m/z 292.0944
[C11H12ClNO3 +Na]+; found: 264.0397. IR Neat: n˜ =1728.2 cmÀ1
.
[C16H15ClNO2 +Na]+; found: 292.0944. IR Neat: n˜ =1739.8 cmÀ1
.
Acknowledgements
3-(4-Fluorophenyl)-5-chloromethyloxazolidin-2-one (6o): Ob-
tained as a pale yellow solid after purification by flash chromatog-
raphy using a solvent system of hexane–EtOAc (5:1) (125 mg,
67%). M.p. 102–1058C (lit. 101–1048C).[4q] 1H NMR (400 MHz, CDCl3,
298 K): d=7.50 (2H, dd J 9.2, 4.6 Hz, ArH), 7.08 (2H, dd J 9.1,
8.3 Hz, ArH), 5.0–4.8 (1H, m, CHO), 4.15 (1H, t J 8.9 Hz, CH2N), 3.94
(1H, dd J 9.1, 5.7 Hz, CH2N), 3.80 (1H, dd J 11.6, 4.1 Hz, CH2Cl),
3.75 ppm (1H, dd J 11.6, 6.6 Hz, CH2Cl). 13C{1H}-NMR (100 MHz,
CDCl3, 298 K) 159.5 (d, J 244.5 Hz), 154.0, 133.9 (d, J 3.2 Hz), 120.2
(d, J 8.1 Hz), 115.9 (d, J 22.6 Hz), 70.8, 48.4, 44.5 ppm. 19F NMR
(376 MHz, CDCl3, 298 K): d=À116.96 ppm (s). Mass spec. (ESI+):
calcd. m/z 230.0379 [C10H9ClFNO2 +H]+; found: 230.0371. calcd.
m/z 252.0198 [C10H9ClFNO2 +Na]+; found: 252.0195. IR Neat: n˜ =
The authors gratefully acknowledge financial support from the
Ministerio de Economía y Competitividad (MINECO), Spain (Grant
No. CTQ2014-51912-REDC and CTQ2014-52899-R) and the Junta
de Comunidades de Castilla-La Mancha, Spain (Grant No. PEII-
2014-013A). Dr. JosØ A. Castro-Osma acknowledges financial sup-
port from the Plan Propio de la Universidad de Castilla-La
Mancha.
Keywords: aluminium
·
heterocycles
·
homogeneous
catalysis · ligand effects · regioselectivity
1740 cmÀ1
.
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3-(4-Bromophenyl)-5-chloromethyloxazolidin-2-one (6q): Ob-
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using a solvent system of first hexane–EtOAc (3:1), then hexane–
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1H NMR (400 MHz, CDCl3, 298 K): d=7.53–7.43 (4H, m, ArH), 4.95–
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.
ChemCatChem 2016, 8, 2100 – 2108
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2107
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Received: April 6, 2016
Published online on May 30, 2016
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