Isocyanurate Formation During Oxazolidinone Synthesis from Epoxides and Isocyanates Catalysed by a Chromium(Salphen) Complex

Article abstract of DOI:10.1002/chem.201702948

Chromium(salphen) complex 10 is found to be a catalyst for the preparation of oxazolidinones from epoxides and isocyanates. Using the optimal reaction conditions (1.5 mol % of chromium(salphen) complex 10 at 80 °C in toluene for 4 hours), six epoxides wer

Full text of DOI:10.1002/chem.201702948

A Journal of
Accepted Article
Title: Isocyanurate Formation During Oxazolidinone Synthesis from
Epoxides and Isocyanates Catalysed by a Chromium(Salphen)
Complex
Authors: Michael North, Jess Mason, and Xiao Wu
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10.1002/chem.201702948
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Isocyanurate Formation During Oxazolidinone Synthesis from
Epoxides and Isocyanates Catalysed by a Chromium(Salphen)
Complex
Xiao Wu,[a] Jess Mason[a] and Michael North*[a]
Abstract: Chromium(salphen) complex 10 is found to be a catalyst
for the preparation of oxazolidinones from epoxides and isocyanates. The reaction of epoxides with isocyanates is one of the most
chemistry,6 as well as being valuable synthetic intermediates.7
Using the optimal reaction conditions (1.5 mol% of
useful and efficient methods for the synthesis of oxazolidinones
(Scheme 1). A number of catalyst systems have been reported
for this reaction, including ammonium salts,8 lanthanide salts,9
lithium halides,10 magnesium halides,11 tetraphenylantimony
iodide12 and trialkyltin halides.13
o
chromium(salphen) complex 10 at 80 C in toluene for 4 hours), six
epoxides were reacted with five isocyanates, providing 15
oxazolidinones in up to 90% yield. With electron-deficient
isocyanates, cyclotrimerisation of the isocyanate to the
corresponding isocyanurates is a competing reaction, showing the
importance of matching catalyst activity to that of the substrates.
Recently, our group has reported a number of highly
efficient metal-based catalysts 8–10 for the formation of cyclic
carbonates from epoxides and carbon dioxide (Figure 1).14,15,16
Compounds 8 and 9 also exhibit excellent catalytic activity for
the preparation of oxazolidinones.5a,b Thus, 5 mol% of bimetallic
aluminium(salen) complex 8 in the absence of a co-catalyst was
found to be an active catalytic system for the synthesis of a
range of mono- and di-substituted oxazolidinones. In the
presence of tetrabutylammonium bromide (5 mol%), aluminium
heterosorpionate complex 9 (5 mol%) was also shown to be an
effective catalyst for the preparation of oxazolidinones. Six
epoxides were reacted with six aromatic isocyanates to give 25
oxazolidinones, showing a broad substrate scope.
Introduction
Epoxides 1 are useful building blocks in organic synthesis and a
number of five-membered heterocycles can be prepared when
they are treated with heterocumulenes. The reaction with carbon
dioxide to furnish either cyclic- or poly-carbonates 2 and 3 has
been extensively studied.1,2,3 Other areas of interest include the
formation of either cyclic dithiocarbonates 4 or trithiocarbonates
5,4 and oxazolidinones 6 and 75 (Scheme 1).
Figure 1. Catalysts for the synthesis of cyclic carbonates and oxazolidinones.
Scheme 1. Synthesis of heterocycles from epoxides and heterocumulenes.
More recently, our group has reported the synthesis of
cyclic carbonates from epoxides and carbon dioxide using
chromium(salphen) complex 10.16 In this case, only 1.5 mol% of
complex 10 was necessary to catalyse the synthesis of a range
of cyclic carbonates, either from monosubstituted epoxides at
room temperature and one bar carbon dioxide pressure, or from
disubstituted epoxides at elevated temperature and pressure. In
view of the high catalytic activity shown by complex 10, we
decided to investigate its use in the related reaction between
epoxides and isocyanates. Herein, we report the use of
chromium(salphen) complex 10 as an efficient catalyst for the
formation of oxazolidinones from epoxides and isocyanates.
Oxazolidinones are an important class of heterocycles and
have been found to be useful compounds in medicinal
[a]
Dr. X. Wu, Miss J. Mason, Professor M. North
Green Chemistry Centre of Excellence, Department of Chemistry
University of York
Heslington, York, YO10 5DD
E-mail: Michael.north@york.ac.uk
Supporting information for this article is given via a link at the end of
the document.
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Results and Discussion
Having determined the optimal reaction conditions for the
synthesis of oxazolidinones 6a and 7a from styrene oxide 1a
and phenyl isocyanate 11a, a series of epoxides was used
together with phenyl isocyanate 11a to give oxazolidinones 6b-g
and 7b-g (Scheme 3). The results of this study are shown in
Screening studies were carried out using styrene oxide 1a and
phenyl isocyanate 11a in a 1:1 ratio under various reaction
conditions (Scheme 2) and the results are shown in Table 1.
Initial experiments were undertaken using 1.5 mol% of both
chromium(salphen) complex 10 and tetrabutylammonium
bromide (TBAB) as a co-catalyst at 80 oC for 24 hour under
solvent-free conditions (Table 1, entry 1). However, the reaction
mixture solidified after 30 minutes. This suggested that a solvent
was necessary to increase the conversion to the oxazolidinone
products. Toluene was selected based on literature precedent5a,b
Table
2.
Functionalised
aliphatic
epoxides
(3-
phenoxypropropylene oxide 1b and epichlorohydrin 1c) and
unfunctionalised aliphatic epoxide 1d were all excellent
substrates, giving high conversions and excellent regioselectivity
to the 3,5-isomers 6b-d (Table 2, entries 2-4). In contrast,
glycidol 1e was found to be a poor substrate, giving a complex
mixture from which no product could be isolated (Table 2, entry
5). When aromatic epoxides 1f and 1g, containing a halogen at
the para-position were used as substrates, good conversions
were obtained though with no regioselectivity (Table 2, entries 6
and 7).
o
and the reaction mixture was heated to 80 C. After 24 hours,
75% conversion was obtained (Table 1, entry 2). Control
experiments proved to be very informative. In the absence of
TBAB, chromium(salphen) complex 10 was able to catalyse the
reaction itself and a 90% conversion was achieved, whereas in
the absence of complex 10, only 7% conversion was observed
(Table 1, entries 3 and 4). Increasing the catalyst loading to 2.5
mol% was not beneficial while lowering the catalyst loading to
0.5 mol% resulted in low conversion (Table 1, entries 5 and 6).
To further optimise the reaction conditions, a sample was taken
after each hour and it was found that the reaction reached
maximum conversion after 4 hours. It was therefore decided that
o
1.5 mol% of catalyst 10 and heating in toluene at 80 C for 4
hours were the optimal reaction conditions for the synthesis of
oxazolidinones from epoxides and isocyanates.
Scheme 3. Reaction of epoxides 1a-g with phenylisocyanate 11a.
Table 2. Synthesis of oxazolidinone 6a-g and 7a-g using epoxide 1a-g.[a]
Entry
Epoxide
Conversion[b] (%)
Yield[c] (%)
1a R1 = Ph
1b R1 = CH2OPh
1c R1 = CH2Cl
90 (35:65)
80 (1:0)
100 (1:0)
100 (92:8)
0
6a,7a (65)
6b (62)
6c (90)
6d (59)
-
1
2
3
4
5
6
7
Scheme 2. Reaction of styrene oxide 1a with phenylisocyanate 11a.
1d R1 = C8H17
Table 1. Optimisation of the synthesis of oxazolidinones 6a and 7a using
complex 10 and TBAB.
1e R1 = CH2OH
1f R1 = 4-ClC6H4
1g R1 = 4-BrC6H4
Complex
10 (mol%)
TBAB
(mol%)
t
Toluene
(mL)
Conversion[a]
(%)
Entry
6a:7b[a]
75 (1:1)
70 (1:1)
6f, 7f (59)
6g, 7g (62)
(h)
1
2
3
4
5
6
7
1.5
1.5
1.5
0
1.5
1.5
0
24
24
24
24
24
24
4
0
70
75
90
7
50:50
66:34
35:65
75:25
50:50
50:50
35:65
0.5
0.5
0.5
0.5
0.5
0.5
[a] Reactions were carried out using 1.5 mol% chromium(salphen)
complex 10 in toluene at 80 oC for 4 hours. [b] Determined by 1H NMR
spectroscopy of the unpurified reaction mixture and figure in brackets is
the ratio of
chromatography.
6:7. [c] Yield of isolated product after purification by column
1.5
0
2.5
0.5
1.5
88
28
90
0
To further expand the substrate scope, styrene oxide 1a
and epichlorohydrin 1c were selected as representative aromatic
and aliphatic epoxides respectively for the synthesis of
oxazolidinones from various isocyanates (Scheme 4). Five
substituted aromatic isocyanates 11b-f and two aliphatic
isocyanates 11g and 11h were reacted with these epoxides and
0
[a] Conversion of epoxide 1a into 6a and 7a and ratio of 6a:7a were
determined by 1H NMR spectroscopy of the unpurified reaction mixture
.
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the results are summarised in Table 3. It was found that
aromatic isocyanates 11b,c gave good to excellent conversions
after 4 hours. A 1:1 ratio of 3,4- and 3,5- regioisomers was
observed when styrene oxide 1a was used, while with
epichlorohydrin 1c, complete regioselectivity for the 3,5-isomer
was achieved (Table 3, entries 1-5 and 8-12). In comparison, no
conversion was obtained when aliphatic isocyanates 11g,h were
used (entries 6,7 and 13,14). With aromatic isocyanates that
have halogen groups at the para-position, chromium(salphen)
complex 10 was found to catalyse the formation of both
oxazolidinones and isocyanurates (perhydro-1,3,5-triazine-2,4,6-
triones) 12 (Figure 2) (Table 3, entries 3-5). Isocyanurates are
known to enhance the physical properties of polyurethanes and
coating materials,17 typically by increasing their flame retardation
and filming characteristics, and commercial products containing
polymeric isocyanurates have increased chemical and thermal
resistance.18
isocyanurates 12a-c proved difficult, the isolated yields of these
oxazolidinones were less than satisfactory (Table 3, entries 10-
12). The formation of isocyanurates as by-products from the
reaction between epoxides and isocyanates has not previously
been reported.
A control experiment using 4-fluorophenyl
isocyanate 11d in the presence of chromium complex 10 under
the standard reaction conditions but in the absence of an
epoxide also gave isocyanurate 12a, indicating that chromium
complex 10 is a strong Lewis acid and capable of catalysing the
cyclotrimerisation of isocyanates. In the absence of chromium
complex 10, only the starting material 4-fluorophenyl isocyanate
was recovered. When isocyanates that have an electron-
donating substituent at the para-position such as 11b were used,
the corresponding urea 13 was isolated rather than the
isocyanurate.
Table 3. Synthesis of oxazolidinones 6,7h-u using complex 10.[a]
Conv.[b]
(%)
Entry
Epoxide
Isocyanate
Yield[c] (%)
1a R1 = Ph
1a R1 = Ph
11b R2 = 4-MeOC6H4
11c R2 = 4-MeC6H4
11d R2 = 4-FC6H4
11e R2 = 4-ClC6H4
11f R2 = 4-BrC6H4
11g R2 = CH2Ph
11h R2 = Et
60 (1:1)
90 (1:1)
30 (1:1)
22 (1:1)
23 (1:1)
0
6h, 7h (56)
6i, 7i (62)
7j (12)[d]
7k (10)[e]
7l(10)[f]
1
2
1a R1 = Ph
3
1a R1 = Ph
4
1a R1 = Ph
5
1a R1 = Ph
6
1a R1 = Ph
0
7
1c R1 = CH2Cl
1c R1 = CH2Cl
1c R1 = CH2Cl
1c R1 = CH2Cl
1c R1 = CH2Cl
1c R1 = CH2Cl
1c R 1= CH2Cl
11b R2 = 4-MeOC6H4
11c R2 = 4-MeC6H4
11d R2 = 4-FC6H4
11e R2 = 4-ClC6H4
11f R2 = 4-BrC6H4
11g R2 = CH2Ph
11h R2 = Et
98 (1:0)
96 (1:0)
90 (1:0)
85 (1:0)
90 (1:0)
0
6o (80)
6p (83)
6q (21)[g]
6r (42)
8
9
10
11
12
13
14
Scheme 4. Reaction of epoxides 1a,c with isocyanate 11a-h.
6s (36)
0
[a] Reactions were carried out using 1.5 mol% of chromium(salphen)
complex 10 in toluene at 80 oC for 4 hours. [b] Conversion of epoxides to
oxazolidinones
unpurified reaction mixture and figure in brackets is the ratio of
6,7
determined by 1H NMR spectroscopy of the
Figure 2. Structure of isocyanurates 12 and urea 13.
6:7. [c]
Yield of isolated product after purification by column chromatography. [d]
Mixture of oxazolidinone 7j and isocyanurate 12a in 40:60 ratio. [e] Mixture of
oxazolidinone 7k and isocyanurate 12b in 45:55 ratio. [f] Mixture of
oxazolidinone 7l and isocyanurates 12c in 50:50 ratio. [g] Mixture of
oxazolidinone 6q and isocyanurate 12a in 95:5 ratio.
Isocyanurates have previously been prepared by the
cyclotrimerisation of isocyanates catalysed by species including
organotin19 and organozinc compounds,20 copper and nickel
halides21 and palladium,22 magnesium23 and iron complexes.0
The formation of isocyanurates 12a-c was much less important
when the competing reaction was between epichlorohydrin 1c
and isocyanates than when styrene oxide 1a was used.
However, since the separation of oxazolidinones 6q-s from
The chemo- and regio-selectivities observed when using
complex 10 as a catalyst can be explained by the catalytic
cycles shown in Scheme 5. Complex 10 can act both as a Lewis
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acid and as a source of a good nucleophile (chloride).
Substrates 1 and 11 possess three sites which are susceptible
to nucleophilic attack: both ends of the epoxide and the central
carbon atom of the isocyanate. They also possess two sites for
Lewis acid activation: the epoxide oxygen and the isocyanate
oxygen. For oxazolidinone formation, the chromium(salphen)
species first acts as a Lewis acid, activating the epoxide towards
ring-opening by chloride anion. The regioselectivites observed
with epoxides 1a-g are consistent with ring-opening of the
activated epoxide normally occurring at the less-hindered,
unsubstituted position by an SN2 type mechanism, eventually
giving the 3,5-isomer of the oxazolidinone. However, when R1 is
an aromatic group capable of stabilising a benzylic carbenium
ion, then ring-opening of the epoxide at the more-hindered,
substituted position ultimately leading to the 3,4-isomer of the
oxazolidinone becomes competitive and little or no
regioselectivity is observed. The chromium coordinated alkoxide
then reacts with the isocyanate to form a carbamate and this
ring closes to give oxazolidinone 6 or 7 with regeneration of
catalyst 10. For isocyanurate formation, the isocyanate oxygen
atom coordinates competitively to the metal centre, followed by
the nucleophilic attack of the chloride anion to give a chromium
complexed carbomoyl chloride complex A. Following this, the
nucleophilic nitrogen can then react further with two molecules
of isocyanates before ring-closing with elimination of chloride to
form isocyanurates 12 and regenerate catalyst 10.
SMP3 apparatus. Infrared spectra were recorded on a Bruker
Vertex 70 instrument.
Conclusions
Chromium(salphen) complex 10 was found to catalyse the
formation of oxazolidinones from epoxides and isocyanates in
the absence of a co-catalyst. Compared to previously reported
aluminium(salen) complexes, chromium(salphen) complex 10
appears to be more Lewis acidic. This allows the catalyst
loading to be reduced to 1.5 mol% and the reaction time to be
reduced to 4 hours. However, the enhanced Lewis acidity of
complex 10 causes the reaction to take a different pathway with
electron-deficient isocyanates, leading to the formation of
isocyanurates 12 by a pathway that involves Lewis acid
activation and subsequent trimerisation of the isocyanate rather
than Lewis acid activation of the epoxide. These results illustrate
that although a strongly Lewis acidic catalyst is desirable to
activate the epoxide for the formation of oxazolidinones from
epoxides and isocyanates, the optimal catalyst for the process is
substrate dependent and requires the electronic properties of
both substrates and catalyst to be matched.
Scheme 5. Proposed catalytic cycles for the synthesis of oxazolidinones and
isocyanurates induced by chromium(salphen) complex 10.
General procedure for oxazolidinone synthesis
Epoxide 1a_g (0.83 mmol) and isocyanate 11a_h (0.83 mmol)
were added to a solution of catalyst 10 (0.013 mmol) in toluene
o
(0.5 mL). The resulting mixture was stirred at 80 C for 4 hours.
After being allowed to cool to room temperature, toluene was
removed under pressure to give the crude oxazolidinone
products. The conversion of epoxide to oxazolidinone was
1
determined by H NMR spectroscopy of the crude mixture. The
products were purified by flash chromatography to give
compound 6/7 a-s.
Experimental Section
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).
Catalyst 10 was prepared as previously reported.16 All
other compounds were commercially available and used as
(85 mg, 43%). M.p. 80–82 C (lit. 79–82 C).[5a] 1H NMR (400
MHz, CDCl3)  7.56 (2H, d, J 8.0 Hz, ArH), 7.46–7.37 (7H, m,
ArH), 7.15 (1H, t, J 8.0 Hz, ArH), 5.65 (1H, d, J 8.0, CHO), 4.39
(1H, t, J 8.0 Hz, CH2N), 3.98 (1H, t, J 8.0 Hz, CH2N); 13C (100
o
o
1
supplied. H NMR and 13C NMR were recorded in CDCl3 at 25
oC on a JEOL 400 spectrometer operating at 400 and 100 MHz,
respectively. Melting points were determined using a Stuart
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MHz, CDCl3)  154.7, 138.1, 138.0, 129.1, 129.0, 125.7, 124.2,
118.3, 74.0, 52.7. Mass spec. (ESI): calcd. m/z 240.1019
[C15H14NO2]+; found: 240.1013. calcd. m/z 262.0838
[C15H13NO2+Na]+; found: 262.0831. IR (neat, cm-1): 1745.
CH2N), 3.93 (1H, dd, J 8.0, 7.5 Hz, CH2N); 13C (100 MHz,
CDCl3)  154.4, 137.9, 136.6, 135.0, 129.3, 129.1, 127.1, 124.3,
118.3, 73.3, 52.6. Mass spec. (ESI): Calcd. m/z 296.0449
[C15H12ClNO2+Na]+; found: 296.0449. IR (neat, cm-1): 1733.
3-Phenyl-4-(4-chlorophenyl)-oxazolidin-2-one (7f): Obtained
as a pale yellow solid after purification by flash chromatography
using a solvent system of CH2Cl2–hexane (4:1) (66 mg, 29%).
M.p. 140–143 oC (lit. 140–142 oC).[5b] 1H NMR (400 MHz,
CDCl3)  7.37–7.24 (8H, m, ArH), 7.11–7.07 (1H, m, ArH), 5.38
(1H, dd, J 12.0, 8.0 Hz, CHN), 4.78 (1H, t, J 12.0 Hz, CH2O),
4.17 (1H, dd, J 8.0, 4.0 Hz, CH2O); 13C (100 MHz, CDCl3) 
155.7, 139.4, 136.7, 134.9, 129.6, 129.0, 127.6, 124.9, 120.9,
69.6, 60.1. Mass spec. (ESI): calcd. m/z 274.0629
[C15H13ClNO2]+; found: 274.0633. Calcd. m/z 296.0449
[C15H12ClNO2+Na]+; found: 296.0448. IR (neat, cm-1): 1733.
3-Phenyl-5-(4-bromophenyl)-oxazolidin-2-one (6g): Obtained
as a white 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), (77 mg, 30%). M.p 132–
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).
o
o
(44 mg, 22%). M.p. 80–82 C (lit. 79–82 C).[5a] 1H NMR (400
MHz, CDCl3)  7.40–7.28 (9H, m, ArH), 7.07 (1H, t, J 8.0 Hz,
ArH), 7.15 (1H, t, J 7.4 Hz, ArH), 5.40 (1H, dd, J 8.0, 6.0 Hz,
CHN), 4.79 (1H, t, J 8.0 Hz, CH2O), 4.21 (1H, dd, J 8.0, 6.0 Hz,
CH2O); 13C (100 MHz, CDCl3)  155.9, 138.2, 137.0, 129.4,
128.9, 128.8, 126.2, 120.8, 69.8, 60.7. Mass spec. (ESI): calcd.
m/z 240.1019 [C15H14NO2]+; found: 240.1024. calcd. m/z
262.0838 [C15H13NO2+Na]+; found: 262.0842. IR (neat, cm-1):
1741.
3-Phenyl-5-phenoxymethyloxazolidin-2-one (6b): Obtained as
a yellow solid after purification by flash chromatography using a
solvent system of first hexane–EtOAc (3:1), then hexane–EtOAc
o
o
o
o
(2:1) (218 mg, 93%). M.p. 138–141 C (lit. 139–140 C).[5a] 1H
134 C (lit. 132–134 C).[5b] 1H NMR (400 MHz, CDCl3)  7.58–
NMR (400 MHz, CDCl3)  7.58 (2H, d, J 8.0 Hz, ArH), 7.40 (2H, t, 7.53 (4H, m, ArH), 7.41–7.37 (2H,m, ArH), 7.32–7.29 (2H, m,
J 8.0 Hz, ArH), 7.30 (2H, t, J 8.0 Hz, ArH), 7.16 (1H, t, J 8.0 Hz,
ArH), 7.00 (1H, t, J 8.0 Hz, ArH), 6.91 (2H, d, J 8.0 Hz, ArH),
5.09–4.96 (1H, m, CHO), 4.24–4.19 (3H, m, CH2O, CH2N), 4.09
(1H, dd, J 8.0, 4.0 Hz, CH2N); 13C (100 MHz, CDCl3)  158.0,
154.4, 138.1, 129.6, 129.1, 124.2, 121.7, 118.3, 114.6, 70.3,
67.8, 47.4. Mass spec. (ESI): calcd. m/z 292.0944
[C16H15NO3+Na]+; found: 292.0939. IR (neat, cm-1): 1732.
ArH), 7.18–7.14 (1H, m, ArH), 5.61 (1H, t, J 8.0 Hz, CHO), 4.39
(1H, t, J 8.0 Hz, CH2N), 3.92 (1H, dd, J 8.0, 7.5 Hz, CH2N); 13C
(100 MHz, CDCl3)  154.3, 137.8, 137.1, 132.2, 129.2, 127.3,
124.4 123.2, 118.3, 73.3, 52.5. Mass spec. (ESI): calcd. m/z
339.9944 [C15H12BrNO2+Na]+; found: 339.9940. IR (neat, cm-1):
1726.
3-Phenyl-4-(4-bromophenyl)-oxazolidin-2-one (7g): 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), (82 mg, 32%). M.p. 157–
3-Phenyl-5-chloromethyloxazolidin-2-one (6c): Obtained as a
pale yellow solid after purification by flash chromatography using
a solvent system of hexane–EtOAc (2:1) (158 mg, 90%). M.p.
o
o
o
o
108–110 C (lit. 101–103 C).[5a] 1H NMR (400 MHz, CDCl3) 
7.56 (2H, m, ArH), 7.40 (2H, t, J 8.0 Hz, ArH), 7.17 (1H, t, J 8.0
Hz, ArH), 4.91–4.85 (1H, m, CHO), 4.18 (1H, t, J 8.0, Hz, CH2N),
3.97 (1H, dd, J 8.0, 4.0 Hz, CH2N), 3.81 (1H, dd, J 12.0, 4.0 Hz,
CH2Cl), 3.75 (1H, dd, J 12.0, 4.0 Hz, CH2Cl); 13C (100 MHz,
CDCl3)  153.9, 137.7, 129.2, 124.4, 118.3, 70.8, 48.2, 44.5.
Mass spec. (ESI): calcd. m/z 234.0292 [C10H10ClNO2+Na]+;
found: 234.0296. IR (neat, cm-1): 1728.
158 C (lit. 156–158 C).[5b] 1H NMR (400 MHz, CDCl3)  7.49
(2H, d, J 8.0 Hz, ArH), 7.37_7.25 (4H, m, ArH), 7.19 (2H, d, J 8.0,
ArH), 7.10 (1H, m, ArH), 5.37 (1H, dd, J 8.0, 6.0 Hz, CHN), 4.78
(1H, t, J 8.0 Hz, CH2O), 4.17 (1H, dd, J 8.0, 6.0 Hz, CH2O); 13C
(100 MHz, CDCl3)  155.7, 137.2, 132.6, 129.2, 129.0, 127.9
125.0, 120.8, 116.5, 69.5, 60.1. Mass spec. (ESI): calcd. m/z
339.9944 [C15H12BrNO2+Na]+; found: 339.9943. IR (neat, cm-1):
1728.
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) (135 mg, 59%). M.p. 71–73 C
3-(4-Methoxyphenyl)-5-phenyloxazolidin-2-one
(6h):
Obtained as a pale yellow solid after purification by flash
chromatography using a solvent system of hexane:EtOAc (5:1)
o
(lit. 70– 71 oC).[5a] 1H NMR (400 MHz, CDCl3)  7.54 (2H, d, J 8.0
Hz, ArH), 7.37 (2H, t J 8.0 Hz, ArH), 7.13 (1H, t, J 8.0 Hz, ArH),
4.66–4.61 (1H, m, CHO), 4.08 (1H, t, J 8.0 Hz, CH2N), 3.66 (1H,
dd, J 8.0, 7.5 Hz, CH2N), 1.91–1.68 (2H, m, CH2), 1.42–1.22
(12H, m, 6×CH2), 0.90 (3H, t, J 8.0 Hz, CH3); 13C (100 MHz,
CDCl3)  155.0, 138.4, 129.0, 123.9, 118.1, 73.1, 50.5, 35.0,
31.8, 29.4, 29.2, 29.1, 24.5, 22.6, 14.1. Mass spec. (ESI): Calcd.
m/z 298.1777 [C17H25NO2+Na]+; found:298.1767. IR (neat, cm-
1): 1717.
(66 mg, 28%). M.p. 100–102 C (lit. 105–107 C).[5a] 1H NMR
(400 MHz, CDCl3)  7.46–7.38 (7H, m, ArH), 6.93–6.91 (2H, m,
ArH), 5.63 (1H, t, J 8.0 Hz, CHO), 4.35 (1H, t, J 8.0 Hz, CH2N),
3.94 (1H, dd, J 12.0, 8.0 Hz, CH2N), 3.80 (3H, s, OCH3); 13C
(100 MHz, CDCl3)  156.4, 155.0, 138.2, 131.3, 129.0, 128.9,
125.6, 120.3, 114.3, 74.0, 55.5, 53.3. Mass spec. (ESI): calcd.
m/z 292.0944 [C16H15ClNO2+Na]+; found: 292.0933. IR (neat,
cm-1): 1732.
o
o
3-(4-Methoxyphenyl)-4-phenyloxazolidin-2-one
(7h):
3-Phenyl-5-(4-chlorophenyl)-oxazolidin-2-one (6f): Obtained
as a pale yellow solid after purification by flash chromatography
using a solvent system of CH2Cl2–hexane (4:1) (68 mg, 30%).
M.p. 124–125 oC (lit. 124–126 oC).[5b] 1H NMR (400 MHz, CDCl3)
Obtained as a pale yellow solid after purification by flash
chromatography using a solvent system of hexane–EtOAc (5:1)
o
o
(66 mg, 28%). M.p. 134–136 C (lit. 137–138 C).[5a] 1H NMR
(400 MHz, CDCl3)  7.35–7.23 (7H, m, ArH), 6.78 (2H, d, J 8.0
 7.55 (2H, d, J 8.0 Hz, ArH), 7.43–7.36 (6H, m, ArH), 7.16 (1H, t, Hz, ArH), 5.31 (1H, dd, J 8.0, 6.0 Hz, CHN), 4.77 (1H, t, J 8.0 Hz,
J 8.0 Hz, ArH), 5.63 (1H, t, J 8.0 Hz, CHO), 4.39 (1H, t, J 8.0 Hz, CH2O), 4.22 (1H, dd, J 8.0, 6.0 Hz, CH2O), 3.73 (3H, s, OCH3);
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13C (100 MHz, CDCl3)  156.8, 156.4, 138.1, 129.8, 129.2, 128.8, (400 MHz, CDCl3)  7.43 (2H, d, J 8.0 Hz, ArH), 6.92 (2H, d, J
126.5, 123.3, 114.1, 69.7, 61.3, 55.3. Mass spec. (ESI): calcd.
m/z 2792.0944 [C16H15ClNO2+Na]+; found: 292.0934. IR (neat,
cm-1): 1739.
8.0 Hz, ArH), 4.89–4.83 (1H, m, CHO), 4.17–4.10 (2H, m, CH2N),
3.79 (3H, s, OCH3), 3.78–3.72 (2H, m, CH2Cl); 13C (100 MHz,
CDCl3)  156.6, 154.2, 130.9, 120.4, 114.3, 70.8, 55.5, 48.7,
44.6. Mass spec. (ESI): calcd. m/z 264.0398 [C11H12ClNO3+Na]+;
found: 264.0395. IR (neat, cm-1): 1728.
3-(4-Methylphenyl)-5-phenyloxazolidin-2-one (6i): Obtained
as a white solid after purification by flash chromatography using
a solvent system of hexane–EtOAc (9:1) (68 mg, 32%). M.p. 96–
98 oC (lit. 98–100 oC).[5a] 1H NMR (400 MHz, CDCl3)  7.43–7.41
(7H, m, ArH), 7.18 (2H, d, J 8.0 Hz, ArH), 5.62 (1H, t, J 8.0 Hz,
CHO), 4.35 (1H, t, J 8.0 Hz, CH2N), 3.94 (1H, dd, J 8.0, 7.0 Hz,
CH2N), 2.32 (3H, s, CH3); 13C (100 MHz, CDCl3)  153.9, 141.7,
129.5, 129.3, 128.4, 128.3, 126.6, 121.3, 110.0, 74.0, 52.6, 20.8.
Mass spec. (ESI): calcd. m/z 276.0995 [C16H15NO2+Na]+; found:
279.0991. IR (neat, cm-1): 1735.
3-(4-Methylphenyl)-5-chloromethyloxazolidin-2-one (6p): Ob-
tained as
a pale yellow solid after purification by flash
chromatography using a solvent system of hexane–EtOAc (3:1)
o
o
(170 mg, 83%). M.p. 104–106 C (lit. 104–107 C).[5a] 1H NMR
(400 MHz, CDCl3)  7.42 (2H, d, J 8.0 Hz), 7.19 (2H, d, J 8.0 Hz),
4.89–4.82 (1H, m, CHO), 4.15 (1H, t, J 8.0 Hz, CH2N), 3.92 (1H,
dd, J 12.0, 8.0 Hz, CH2N), 3.89 (1H, dd, J 12.0, 4.0 Hz, CH2Cl),
3.73 (1H, dd, J 12.0, 8.0 Hz, CH2Cl), 2.32 (3H, s, CH3); 13C (100
MHz, CDCl3)  154.0, 135.2, 134.1, 129.6, 118.4, 70.8, 48.3,
44.5, 20.7. Mass spec. (ESI): calcd. m/z 226.0629
[C11H13ClNO2+H]+; found: 226.0630. IR (neat, cm-1): 1732.
3-(4-Methylphenyl)-4-phenyloxazolidin-2-one (7i): Obtained
as a white solid after purification by flash chromatography using
a solvent system of hexane–EtOAc (9:1) (63 mg, 30%). M.p.
o
o
106–108 C (lit. 105–107 C).[5a] 1H NMR (400 MHz, CDCl3) 
7.36–7.20 (7H, m, ArH), 7.03 (2H, d, J 8.0 Hz, ArH), 5.35 (1H,
dd, J 8.0, 6.0 Hz, CHN), 4.76 (1H, t, J 8.0 Hz, CH2O), 4.19 (1H,
dd, J 8.0, 4.0 Hz, CH2O), 2.23 (3H, s, CH3); 13C (100 MHz,
CDCl3)  156.2, 138.3, 134.5, 134.3, 129.5, 129.3, 128.8, 126.3,
121.1, 69.8, 60.8, 20.8. Mass spec. (ESI): calcd. m/z 276.0995
[C16H15NO2+Na]+; found: 279.1005. IR (neat, cm-1): 1739.
3-(4-Fluorophenyl)-5-chloromethyloxazolidin-2-one
(6q):
Obtained as a pale yellow solid after purification by flash
chromatography using a solvent system of hexane–EtOAc (5:1)
(125 mg, 67%). 1H NMR (400 MHz, CDCl3)  7.51 (2H, dd, J 8.0,
4.0 Hz, ArH), 7.09 (2H, t, J 8.0 Hz, ArH), 4.91–4.85 (1H, m,
CHO), 4.16 (1H, t, J 8.0 Hz, CH2N), 3.96 (1H, dd, J 8.0, 4.0 Hz,
CH2N), 3.81 (1H, dd, J 12.0, 4.0 Hz, CH2Cl), 3.75 (1H, dd, J 12.0,
8.0 Hz, CH2Cl); 13C (100 MHz, CDCl3)  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. 19F NMR(376 MHz, CDCl3): 117.8 (s).
Mass spec. (ESI): calcd. m/z 252.0198 [C10H9ClFNO2+Na]+;
found: 252.0195.
3-(4-Fluorophenyl)-4-phenyloxazolidin-2-one (7j): Obtained
as a white solid in a mixture with 12a after purification by flash
chromatography using a solvent system of first hexane–EtOAc
(9:1), then hexane– EtOAc (5:1) (28 mg, 12%). 1H NMR (400
MHz, CDCl3)  7.4–7.25 (7H, m, ArH), 6.95–6.93 (2H, m, ArH),
5.33 (1H, dd, J 12.0, 8.0 Hz, CHN), 4.79 (1H, t, J 8.0 Hz, CH2O),
4.22 (1H, dd, J 8.0, 6.0 Hz, CH2O); 13C (100 MHz, CDCl3) 
161.5, 156.1, 137.8, 133.0, 129.2, 129.0, 126.4, 123.0 (d, J 8
Hz), 115.7 (d, J 23 Hz), 69.8, 61.1; 19F NMR (376 MHz, CDCl3):
117.1 (s). Mass spec. (ESI): calcd. m/z 280.0744
[C15H12FNO2+Na]+; found: 280.0716.
3-(4-Chlorophenyl)-5-chloromethyloxazolidin-2-one
(6r):
Obtained as an orange solid after purification by flash
chromatography using a solvent system of hexane–EtOAc (1:1)
o
o
(100 mg, 42%). M.p. 129–132 C (lit. 130–133 C).[5a] 1H NMR
(400 MHz, CDCl3)  7.49 (2H, d, J 8.0 Hz, ArH), 7.34 (2H, d, J
8.0 Hz, ArH), 4.91–4.85 (1H, m, CHO), 4.14 (1H, t, J 8.0 Hz,
CH2N), 3.93 (1H, dd, J 8.0, 4.0 Hz, CH2N), 3.79 (1H, dd, J 12.0,
4.0 Hz, CH2Cl), 3.75 (1H, dd, J 12.0, 8.0 Hz, CH2Cl); 13C (100
MHz, CDCl3)  153.7, 136.3, 129.6, 129.1, 119.4, 70.8, 48.0,
3-(4-Chlorophenyl)-4-phenyloxazolidin-2-one (7k): Obtained
as a pale yellow solid in a mixture with 12b after purification by
flash chromatography using a solvent system of hexane–EtOAc
(9:1) (22 mg, 10%). 1H NMR (400 MHz, CDCl3)  7.37–7.29 (7H,
44.5.
Mass
spec.
(ESI+):
calcd.m/z
267.9903
m, ArH), 7.21 (2H, d, J 8.0 Hz, ArH), 5.36 (1H, dd, J 12.0, 8.0 Hz, [C10H9Cl2NO2+Na]+; found: 267.9905. IR (neat, cm-1): 1741.
CHN), 4.79 (1H, t, J 8.0 Hz, CH2O), 4.21 (1H, dd, J 8.0, 6.0 Hz,
CH2O); 13C (100 MHz, CDCl3)  155.8, 137.7, 135.6, 129.7,
129.6, 128.9, 126.2, 121.9, 69.8, 60.6. Mass spec. (ESI): calcd.
m/z 296.0449 [C15H12ClNO2+Na]+; found: 296.0453.
3-(4-Bromophenyl)-5-chloromethyloxazolidin-2-one
(6s):
Obtained as yellow solid after purification by flash
a
chromatography using a solvent system of first hexane–EtOAc
(3:1), then hexane–EtOAc (2:1) (92 mg, 36%). M.p. 126–128 oC
(lit. 125–128 oC).[5a] 1H NMR (400 MHz, CDCl3)  7.51–7.44 (4H,
m, ArH), 4.92–4.86 (1H, m, CHO), 4.15 (1H, t, J 8.0 Hz, CH2N),
3.94 (1H, dd, J 8.0, 4.0 Hz, CH2N), 3.80 (1H, dd, J 12.0, 4.0 Hz,
CH2Cl), 3.75 (1H, dd, J 12.0, 8.0 Hz, CH2Cl); 13C (100 MHz,
CDCl3)  153.7, 132.7, 132.1, 119.7, 117.3, 70.8, 48.0, 44.4.
Mass spec. (ESI+): calcd. m/z 311.9397 [C10H9BrClNO2+Na]+;
found: 311.9389. IR (neat, cm-1): 1732.
3-(4-Bromophenyl)-4-phenyloxazolidin-2-one (7l): Obtained
as a yellow solid in a mixture with 12c after purification by flash
chromatography using a solvent system of hexane–EtOAc (9:1)
o
o
(26 mg, 10%). M.p. 132–135 C (lit. 134–137 C).[5a] 1H NMR
(400 MHz, CDCl3)  7.37–7.37 (9H, m, ArH), 5.35 (1H, dd, J 8.0,
6.0 Hz, CHN), 4.79 (1H, t, J 8.0 Hz, CH2O), 4.21 (1H, dd, J 8.0,
6.0 Hz, CH2O); 13C (100 MHz, CDCl3)  156.2, 132.7, 131.8,
130.0, 129.5, 128.5, 126.0, 123.7, 122.2, 67.2, 61.8. Mass spec.
(ESI): calcd. m/z 318.0124 [C15H12BrNO2+H]+; found: 318.0130.
3-(4-Methoxyphenyl)-5-chloromethyloxazolidin-2-one (6o):
Keywords: oxazolidinone • isocyanurate • chromium • epoxide •
catalysis
Obtained as
a
yellow solid after purification by flash
chromatography using a solvent system of hexane–EtOAc (3:1)
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Entry for the Table of Contents (Please choose one layout)
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Xiao Wu, Jess Mason and Michael
North*
Page No. – Page No.
Isocyanurate Formation During
Oxazolidinone Synthesis from
Epoxides and Isocyanates Catalysed
by a Chromium(Salphen) Complex
A tale of two reactions. A chromimium(salphen) complex catalyses the formation
of oxazolidinones from epoxides and isocyanates. However, with particularly
electron-deficient isocyanates, the complex catalyses cyclotrimerisation of the
isocyanate to an isocyanurate instead.
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