Superbase catalysis of oxazolidin-2-one ring formation from carbon dioxide and prop-2-yn-1-amines under homogeneous or heterogenous conditions

Article abstract of DOI:10.1039/a800453f

N-alkyl-substituted prop-2-yn-1-amines and N-tri-, tetra- and penta-alkyl-substituted guanidines or other strong organic bases assemble under the action of carbon dioxide to afford carbamates, from which methyleneoxazolidinones 2 are formed by ring closure. If alkyl or cycloalkyl chains of appropriate length are present in the guanidines the reaction readily occurs under heterogenous conditions without solvent.

Full text of DOI:10.1039/a800453f

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Superbase catalysis of oxazolidin-2-one ring formation from carbon
dioxide and prop-2-yn-1-amines under homogeneous or heterogenous
conditions
Mirco Costa,* Gian Paolo Chiusoli, Davide Taffurelli and Giulio Dalmonego
Dipartimento di Chimica Organica e Industriale, Università degli Studi di Parma,
Viale delle Scienze, 43100 Parma, Italy
N-alkyl-substituted prop-2-yn-1-amines and N-tri-, tetra- and penta-alkyl-substituted guanidines or other
strong organic bases assemble under the action of carbon dioxide to afford carbamates, from which
methyleneoxazolidinones 2 are formed by ring closure. If alkyl or cycloalkyl chains of appropriate length
are present in the guanidines the reaction readily occurs under heterogenous conditions without solvent.
᎐
Table 1 Catalytic reaction of amine HC᎐CC(Me)2NHCH2Ph 1f with
᎐
Introduction
CO2 in the presence of strong bases in acetonitrilea
We have recently shown that the catalytic use of superbases
allows the direct introduction of carbon dioxide into acetylenic
amines1 under mild conditions in acetonitrile to give fair to
excellent yields of 2, corresponding to 5-exo-dig ring closure in
agreement with Baldwin’s rules.2 A few percent of 3 (6-endo-
dig cyclization) is formed only in stoichiometric reactions at
temperatures higher than 100 ЊC, see Scheme 1.
6
Entry
Base (MeCNpKBHϩ
)
Conversion (%)b
2f Yield (%)c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
5b (25.44)
4b (24.2)
5a (25.95)
4a (23.75)
6 (24.33)
10 (42.60)
11 (27.58)
8d
>99
95
89
75
80
90
55
68
>99
98
81
>99
79
48
95
99
>99
89
83
78
64
75
83
50
60
89
87
76
89
74
42
88
88
89
R1
N
R1
CHR
+
R
R2
R3
4kd
R2
B
R
C(R1R2)NHR3
CO2
9d
+
N
O
O
R3
4ld
1
4fd
O
O
4cd
3
B = organic superbase
2
4dd
R = H; R1 = R2 = H; R3 = Me
b R = H; R1 = R2 = H; R3 =Bun
c R = H; R1 = R2 = H; R3 = CH2Ph
1a
4ed
4gd
4hd
d R = H; R1 = H; R2 = Me; R3 = Bun
e
f
g
h
i
R = H; R1 = R2 = Me; R3 = Bun
R = H; R1 = R2 = Me; R3 = CH2Ph
R = H; R1 = R2 = Me; R3 = n-C6H13
a Reaction conditions: 80 ЊC, 6 bar CO2, 6 h; amine 1f (2 mmol, amine:
base molar ratio 10:1, base conc. 0.125 mol dmϪ3). b With respect to the
starting acetylenic amine. c Yield of isolated products with respect to
R = H; R1 = R2 = Me; R3 = CH2CH=CH2
R = Me; R1 = R2 = H; R3 = CH2Ph
the starting acetylenic amine. d pKBH values are not available but
ϩ
should be placed between 24.5 and 23.5.
Scheme 1
R
R
The use of strong bases able to stabilize the intermediate
carbamate anion was the key for the success of this reaction.
We now report additional results and new developments includ-
ing the generation of hydrophobic regions between the sub-
strate and superbase, which allow the reaction to be carried out
in the presence of water much alike enzyme catalysis. Further
information about the intermediates involved and the role of
hydrogen bridges are also provided.
R1
1 + CO2 + B
N
O
BH+
–
O
Scheme 2
N
N
O
O
Results and discussion
H+
–
N
R
Reactions in homogeneous solution
With carbon dioxide. The reactions can be performed in
organic solvents able to dissolve the carbamates formed from
the secondary acetylenic amine, carbon dioxide and the strong
base (Scheme 2).
ϩ
To our knowledge, pKBH measurements of guanidines 4c–
h,k,l, 8 and 9 have not been reported. However, on the basis of
ϩ
The model we chose was based on the interaction of an acid
with a guanidine compound, which has been recently reported,3
and that we assumed to be also valid for the carbamic acid case.
As previously observed1 some strong bases especially those
previous studies pKBH values can be confidently assumed to be
not very different from those of the corresponding methyl-
ϩ
substituted guanidines for which pKBH values near 13.4–13.9
have been obtained in water.4 Slightly lower values than those
found for methylated guanidines should be expected however:
methyl group homologues cause a slight decrease in basicity
according to the trend observed with primary amines.5a The
ϩ
having pKBH у 24 in acetonitrile gave satisfactory yields
under very mild reaction conditions. Table 1 summarizes yields
and conversions of catalytic reactions using superbases of
different nature and strength.
ϩ
differences in the pKBH values of various guanidines in
J. Chem. Soc., Perkin Trans. 1, 1998
1541

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1
2
3
᎐
᎐
Table 2 Stoichiometric reaction of amine HC᎐CC(Me)2NHCH2Ph 1f
Table 3 Reaction of different amines [RC᎐CC(R R )NHR ] 1 with
᎐
᎐
with CO2 in the presence of strong bases in acetonitrilea
CO2 and 4aa
Base
MeCNpKBH
Conversion
(%)b
2f Yield
3f Yield
Conversion
6
(%)b
(%)b
Entry
Starting material
(%)b
Product 2 Yield (%)c
ϩ
Entry
(
)
1
2
3
4
5
6
7
8
9
5b (25.44)
4b (24.2)
5a (25.95)
4a (23.75)
6 (24.33)
10 (42.60)
11 (27.58)
4i (17.90)
7 (18.50)
>99
93
92
92
83
75
78
46
18
4
3
3
2.5
2
2
—
—
8
1
2
3
4
5
6
1a
1d
1e
1f
1h
1i
69
75
90
91
70
25
2a
2d
2e
2f
2h
2i
58d
70d
83
>99
>99
>99
90
91
59
79
60
18e
30
10
a Reaction conditions: 110 ЊC, 5 bar CO2, 24 h, acetylenic amine
(2 mmol, amine:base molar ratio 10:1, base conc. 0.045 mol dmϪ3).
b With respect to the starting acetylenic amine. c Isolated products with
—
a Reaction conditions: 110 ЊC, 10 bar CO2, 24 h, amine 1f (1 mmol, base
respect to the starting acetylenic amines. d Base conc. 0.2 mol dmϪ3
.
conc. 0.2 mol dmϪ3). b By GLC based on the starting acetylenic amine.
e At 140 ЊC for 48 h, base conc. 0.2 mol dmϪ3
.
Y
N
tory results. Thus, some ring-containing pentaalkyl-substituted
guanidines work better than the tetraalkyl ones (compare
entries 1, 2, 10 and 15 with 3, 4 and 8) even in the case when the
X1
X3
ϩ
X2
X4
latter have higher pKBH values (compare entries 1 and 3).
However, elongating one aliphatic chain in pentalkylguanidines
gives less satisfactory results (entries 13 and 14). Good results
are obtained with trialkylguanidines (entries 9, 12, 16, 17 and,
to a lesser extent, 11). The effect of basicity is apparent with the
4
4a X1 = X2 = X3 = X4 = Me, Y = H
4b X1 = X2 = X1 = X4 = Me, Y = Pr
4c X1 = X2 = X3 = X4 = Me, Y = octyl
X1 = X2 = X3 = X4 = Me, Y = dodecyl
ϩ
phosphorus bases 10 and 11 (entries 6 and 7) where 10 (pKBH
4d
4e X1 = X2 = X3 = X4 = Me, Y = cyclohexyl
4f X1 = X3 = H, X2 = X4 = Pri, Y = dodecyl
4g X1 = X3 = H, X2 = X4 = Pri, Y = cyclohexyl
4h X1 = X3 = H, X2 = X4 = Y = Pri
ϩ
42.60) gives a higher yield than 11 (pKBH 27.58). The amidine
6 (entry 5) also behaves satisfactorily. In conclusion the course
of the reaction turns out to be influenced not only by basicity
but also by other structural effects probably ascribable to steric
hindrance and to hydrogen bridges as will be discussed later.
Under more drastic conditions and with stoichiometric ratios
of the base, high yields of 2 were usually attained together with
small amounts of the six-membered ring 3 as shown in
X1 = X3 = Y = H, X2 = X4 = Ph
4i
4k
4l
X1 = X3 = H, X2 = X4 = Y = cyclohexyl
X1 = X3 = H, X2 = X4 = cyclohexyl, Y = dodecyl
N
5a R = H
5b R = Me
N
ϩ
Table 2. Guanidines with high pKBH values did not differ very
N
N
R
N
N
strongly from each other in activity (entries 1–4), however.
Lower yields were obtained with 4i and 7 (entries 8, 9) likely
owing to their lower basicity, and with 11, likely as a con-
sequence of its steric bulk (entry 7).
H
5
6
7
The dependence of the yield of 2 on the superbase concen-
tration has also been studied using bases 5a and 10 with amine
1f (10:1 molar ratio) at 80 ЊC under 6 bar of CO2 for 6 h. The
results indicate that the yield of 2f increases from 27 to 89% on
increasing the concentration of superbase 5a from 0.02 to 0.12
mol dmϪ3 and from 20 to 83% on increasing the concentration
N
N
N
N
H
N
N
of superbase 10 from 0.03 to 0.12 mol dmϪ3
.
The reaction was unsuccessful in weakly polar solvents such
as toluene and THF. The use of aprotic polar solvents such as
N,N-dimethylacetamide, N-methylpyrrolidone and above all
acetonitrile gave the best results.
8
9
N
Alkyl substituents in the propynyl group of the starting
material also exert an important effect on the course of the
reaction. The results of catalytic reactions carried out at 110 ЊC
for 24 h under 5 bar CO2 pressure in acetonitrile in the presence
of 4a (1:10 molar ratio with the amine) are reported in Table 3.
The best yields were attained with geminal methyl groups
(1,1-disubstituted) in the starting material (entries 3,4). Sub-
stituents at the terminal position of the triple bond strongly
decrease the yield (entry 6).
N
P
N
N
N
N
N
P
N
P
N
N
N
P
N
P
N
N
N
N
11
N
10
With sodium hydrogen carbonate and NBu4Br. The reaction
described above can also be carried out using sodium hydrogen
carbonate as CO2 carrier. The best results were obtained,
however, by adding NBu4Br as phase transfer agent for the
hydrogen carbonate anion from the solid to the liquid phase
(Table 4).
acetonitrile should also be small as found in water, although
distributed over a larger range.5b Taking into account that
1,1,3,3-tetramethylguanidine has a pKBH = 23.75 in aceto-
nitrile, pentamethylguanidine = 25 and propyltetramethylguan-
idine = 24.2, values between 23.5 and 24.5 should cover all the
range of substituted guanidines used in the present work.6 This
seems sufficient for the present study because as we shall see,
basicity is not the only factor influencing the reaction described
here; other conditions need to be considered to obtain satisfac-
ϩ
Reactions in water
With carbon dioxide. Since the reaction involves the formation
of a carbamate anion, which carries out the attack on the triple
bond, it is strongly inhibited by the presence of water and
1542
J. Chem. Soc., Perkin Trans. 1, 1998

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Table 5 Reaction of N-alkylpropynamines 1 with CO2 in the presence
of guanidine bases and watera
᎐
Table 4 Catalytic reaction of amine HC᎐CC(Me)2NHCH2Ph 1f with
᎐
NaHCO3 in the presence of strong bases and NBu4Br in acetonitrilea
NaHCO3 :1f
molar ratio
Conversion
(%)b
2f Yield
Amine 1
Entry (mmol)
Base
(mmol)
Conversion
(%)b
2 Yield
Entry
Base
(%)b
(%)b
1
2
3
4
5
6
9
6
64
97
52
92
55
63
95
50
90
54
98
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
1a (2.0)
1a (2.0)
1b (2.0)
1b (2.0)
1c (2.0)
1c (2.5)
1c (2.0)
1e (2.0)
1e (2.0)
1e (2.0)
1e (2.0)
1e (2.0)
1e (2.0)
1e (2.0)
1e (2.0)
1g (2.0)
1f (2.0)
1f (2.0)
1f (2.0)
1f (2.0)
1f (2.0)
1f (2.0)
1f (2.0)
4a (2.0)
8 (2.0)
8 (2.0)
8 (0.5)
8 (2.0)
8 (0.1)
8 (0.5)
8 (2.0)
8 (0.5)
8 (2.0)
8 (2.0)
4c (2.0)
4c (0.5)
4e (0.5)
4b (0.5)
4c (2.0)
4a (2.0)
8 (2.0)
9 (2.0)
4c (2.0)
4c (0.5)
4c (2.0)
4f (2.0)
1
33
97
88
97
94
78
93
82
87
4
78
53
50
18
54
4
2a <1
2a 31
2b 95
2b 87
2c 96
2c 93
2c 77c
2e 91
2e 80
2e 86c
2e 3d
2e 75c
2e 51
2e 47
2e 16
2g 52
9
6 ϩ NBu4Br
6
6 ϩ NBu4Br
6
6 ϩ NBu4Br
8
8
41
41
>99
a Reaction conditions: 80 ЊC, 15 h, amine (2 mmol, amine:base molar
ratio 10:1, base conc. 0.067 mol dmϪ3, NBu4Br:base molar ratio 2:1,
CH3CN 1.5 ml). b By GLC based on the starting acetylenic amine.
hydrogen donors in general. On the other hand reactions of this
kind are commonly effected by enzyme systems in the presence
of water.7 This is attributed to the formation of segregated sites,
formed by taking advantage of both hydrophobic regions and a
hydrogen bond network,8,9 where water is prevented from inter-
fering adversely with the reaction center.We wondered whether
an appropriate, though not necessarily so efficient, site could be
generated for the reaction under study in the presence of water.
Carbon dioxide itself could be responsible for joining together
the two reactive partners to create a hydrophobic site. To this
end we had to design proper substrates and bases B whose
assembly could ensure the exclusion of water and the access of
carbon dioxide.
2f
3
94
86
79
68
73
2f 92
2f 80
2f 75
2f 66
2f 71c
2f 94
>99
a Reaction conditions: 70 ЊC, 20 bar CO2, 24 h, 2.5 ml water for 2.0
mmol of amine 1. Increasing the amount of water led to longer reaction
times but did not affect yields significantly. b By GLC based on the
starting acetylenic amine. c At atmospheric pressure of carbon dioxide.
d At room temperature and atmospheric pressure of CO2.
We ascertained that by reaction with carbon dioxide, second-
ary propynamines and properly sized tetra- or pentaalkyl-
guanidines form the corresponding guanidinium carbamates,
which are able to segregate so effectively from water to allow
intramolecular incorporation of the intermediate carbamate
into an oxazolidine ring by reaction with the triple bond, even
in the absence of added carbon dioxide. Thus N-benzyldi-
methylpropynamine 1f (1.0 mmol) and guanidine 8 (1.0 mmol)
were allowed to react stoichiometrically with CO2 (1 bar) at
room temperature in the presence of water (1.8 ml), then the
mixture containing the carbamate was heated at 70 ЊC in the
absence of added CO2 to obtain a 20% yield of 2f. Operating a
one-pot reaction under carbon dioxide gave good results as
shown in Table 5. Thus 1e (2.0 mmol) reacted with carbon
dioxide (20 bar) in the presence of base 8 (2.0 mmol) in water (1.5
ml) at 70 ЊC for 24 h under stirring in an autoclave (45 ml cap-
acity) giving product 2e in 91% yield (entry 8). With 1b and 1c
the yield was even higher (95%, entry 3, and 96%, entry 5), in
contrast with that observed with 4a in acetonitrile (Table 4)
where the geminal R1 and R2 groups were found to exert a posi-
tive effect (this result points to the importance of the shape of
the hydrophobic region in the presence of water). Interestingly
the reaction could be made catalytic using 2.5 mmol of 1c and
0.1 mmol of 8 under the same conditions still maintaining a
good yield (93%, entry 6). The same reaction (4:1 substrate to
guanidine molar ratio) could be carried out at atmospheric
pressure of CO2 at 70 ЊC for 24 h giving 2c in 77% yield (entry 7;
for other catalytic reactions, which were not optimized, compare
entries 4, 9, 13, 14, 15 and 21). As expected the reaction of
alkynamines and guanidines having short alkyl chains was
not satisfactory, for example N-methylprop-2-ynamine 1a or
N-benzyl-1,1-dimethylprop-2-ynamine 1f and tetramethyl-
guanidine (4a) in stoichiometric amounts in the presence of
water gave <1% and 3% yield of 2a and 2f, respectively (entries
1 and 17). The presence of medium-sized alkyl chains such as
n-butyl or benzyl groups at the nitrogen of propynamines is
beneficial (entries 3, 5, 8, 18). Longer chains (C10) have a
negative effect. Thus the stoichiometric reaction of N-
decyldimethylpropynamine with carbon dioxide and base 4c,
under the reported conditions, gave a 2% yield of 2. On the other
hand cyclic or long-chain aliphatic groups replacing hydrogen in
one NH group of tetramethylguanidine such as 4c and 4e as well
as other variants (8, 9) exert a positive effect (compare entries 1,
2; 14, 15; 17, 18; 20–23). Replacing all the methyl groups with
n-octyl chains gives negative results (less than 1% yield of 2f).
These limitations are likely to be related to the need for preserv-
ing easy access of carbon dioxide to the reaction center.
With sodium hydrogen carbonate and NBu4Br. The same type
of reactions as described above were tried using sodium hydro-
gen carbonate as CO2 carrier. The best results were obtained as
in the case of the homogeneous solution by adding NBu4Br as
phase transfer agent. Table 6 shows the results.
The results suggest that a complex interplay of factors con-
trol carbon dioxide incorporation, including strength of the
base used, hydrogen bonding, size and shape of the catalytic
assembly and hydrophobicity. While the superbase is required
to stabilize the carbamate first formed, hydrogen bonds can be
important to reinforce the assembly, particularly in the presence
of water, a circumstance also requiring suitable substituents
both in the base and in the acetylenic amine to warrant sufficient
hydrophobicity while preserving facile access of carbon dioxide
to the reaction center. Taking as an example the reaction of 1e
in the presence of water it can be observed that tetraalkyl-
guanidine 8 (with one hydrogen on a nitrogen atom) works
better than the pentaalkyl one 9 (compare entries 5 and 10, and
6 and 11 of Table 6). This is in contrast with what happens in
acetonitrile, where the opposite was found to be true, as shown
by comparative experiments, which were carried out at atmos-
pheric CO2 pressure to magnify the differences. Thus 1e reacted
with carbon dioxide at atmospheric pressure in the presence of
pentaalkylguanidine 9 (1 mol per mol of 1e), in acetonitrile at
70 ЊC for 3 h, to give oxazolidinone 2e in 55% yield, while with
tetraalkylguanidine 8, under the same reaction conditions, the
yield was 32%. Working at atmospheric pressure of carbon
dioxide at 70 ЊC for 7 h with water in place of acetonitrile
pentaalkylguanidine 9 gave an 18% yield of 2e, while the
tetraalkyl one (8) gave a 68% yield of 2e. This behaviour can
possibly be traced to the effect of hydrogen bonds in the inter-
mediate guanidinium carbamate.
In the presence of water two hydrogen bonds, such as those
resulting from the carbamate interaction with 8, are more
J. Chem. Soc., Perkin Trans. 1, 1998
1543

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Table 6 Catalytic reaction of acetylenic amines 1e and 1f with
out with a Carlo Erba Elemental Analyser Model EA 1108.
NaHCO3 in the presence of strong bases and NBu4Br in watera
Infrared spectra were recorded with a Nicolet 5PCFT-IR
spectrophotometer. Mass spectra were obtained using a
Hewlett Packard Mass Selective Detector 5971 Series interfaced
with a Hewlett Packard 5890 Series II GC or a FinniganMat
SSQ 710 spectrometer both at 70 eV ionising voltage. 1H NMR
spectra were recorded at 300 MHz and 13C NMR spectra at 75
MHz on a Bruker AC 300 spectrometer with Me4Si as an
internal reference. Chemical shifts and coupling constants (J)
are given as δ values (ppm) and in Hz respectively. The reaction
mixtures were analysed by GLC using a capillary column with
methylsilicone (OV101) as stationary phase or by TLC (SiO2).
Quantitative determinations were carried out by GLC using the
internal standard method or by weighing the isolated prod-
ucts. Merck silica gel 60 (60–230 mesh) was used for column
chromatography. Analytical TLC plates and silica gel 60F 254
was purchased from Merck. N-Methylprop-2-ynamine 1a, 1,1-
dimethylprop-2-ynamine, prop-2-yn-1-ol, 2-methylbut-3-yn-2-
ol, and but-3-yn-2-ol are commercial products (Aldrich, Acros-
Carlo Erba). Acetonitrile was dried over 3 Å molecular sieves.
Alkyl and cycloalkyl primary amines, piperidine, tetramethyl-
urea, diisopropylurea, dicyclohexylcarbodiimide, diisopropyl-
carbodiimide, triphosgene, 4a, 4i, 5a, 5b, 6, 7, 10 and 11 are
commercially available products (Aldrich, Fluka, Acros-Carlo
Erba) and were used without further purification.
NaHCO3 :Amine Conversion
Entry Amine 1 Base molar ratio
2 Yield
(%)b
(%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
1f
1f
1f
1f
1e
1f
1f
1f
1f
1e
1f
1f
1f
1f
1e
1f
1e
1f
1f
4d
4c
4c
9
6
6
57
38
85
30
33
60
59
88
83
64
95
7
2f 56
2f 38
2f 83
2f 30
2e 31
2f 58
2f 58
2f 83
2f 81
2e 60
2f 92
6 ϩ NBu4Br
6
6
6 ϩ NBu4Br
4
4 ϩ NBu4Br
6
9
9
8
8
8
8
6
8
6 ϩ NBu4Br
6
4k
4k
4l
4l
4f
4f
4h
4g
2f 6
6 ϩ NBu4Br
47
86
82
>89
76
3
2f 43
2f 85
2e 81
2f 89
2e 75
6
6
6
6
6
6
2f
2
22
2f 21
a Reaction conditions: 80 ЊC, 15 h, amine:base molar ratio 10:1, base
conc. 0.067 mol dmϪ3, NBu4Br:base molar ratio = 2:1, 1.5 ml water.
b By GLC based on the starting acetylenic amine.
R2
R
Synthesis of acetylenic amines
R3
N
H
H
O
N-Butylprop-2-ynamine 1b, N-benzylprop-2-ynamine 1c and
N-butyl-1-methylprop-2-ynamine 1d were prepared by reaction
of prop-2-ynyl toluene-p-sulfonate or 1-methylprop-2-ynyl
toluene-p-sulfonate with the respective amine according to a
procedure reported in the literature.11 N-Butyl-1,1-dimethyl-
prop-2-ynamine 1e, N-hexyl-1,1-dimethylprop-2-ynamine 1g
and N-allyl-1,1-dimethylprop-2-ynamine 1h were prepared
from 1,1-dimethylprop-2-ynyl acetate and the respective amine
according to the literature.12 N-Benzyl-1,1-dimethylprop-2-
ynamine 1f was prepared according to the conventional pro-
cedure of alkylation of primary amines with alkyl halides. Thus
an excess of 1,1-dimethylprop-2-ynamine (13 g, 160 mmol) was
allowed to react with benzyl chloride (7 g, 60 mmol) in dry THF
(50 ml) at 60 ЊC for 15 h. A white solid (mp 47 ЊC, 6.5 g, 63%)
was recovered after acid-base extraction. N-Benzylbut-2-
ynamine 1i was prepared from 1-bromobut-2-yne and benzyl-
amine as reported in the literature.11
R
+
–
N
R4
N
N
R2
O
R1
effective than one probably because, even in a transient way,
they can reinforce the hydrophobic assembly against the inter-
ference of water. With 1f, however, which has an N-benzyl
group in place of an N-n-butyl the effect is less apparent (entries
18 and 19 of Table 5) because of the higher hydrophobicity of
the former. In the homogeneous solution in acetonitrile two
hydrogen bonds tend to hamper the subsequent reaction of the
carbamate anion with the triple bond by reducing its nucleo-
philicity, and so one hydrogen bridge turns out to be better. The
situation appears to be more complex than suggested by the
above interpretation, however. In fact when two protons (plus
one coming from protonation) are present in certain bases such
as in 4k and 4g the reaction in the presence of water gives poor
results (Table 6, entries 12 and 19), while excellent results are
obtained in acetonitrile (Table 1, entries 9 and 16). In the for-
mer case it is likely that solubility in water becomes too high (as
with guanidines containing short allkyl chains) and this is con-
firmed by the fact that 4l and 4f which have similar structure but
possess a long aliphatic chain instead of a cyclohexyl group the
yield is high again (Table 6, entries 14 and 16). In the latter case
(reaction in acetonitrile) it is possible that more efficient cat-
alysis is exerted by the formation of more complex aggregates
held by additional hydrogen bonds. This is only a hypothesis,
however, which requires further investigation. Hydrogen bonds
are known to stabilize transition states in enzyme reactions.10
Hamilton11 has reported such interactions in hydrophobic sys-
tems. We are not able at present to estimate the extent to which
hydrogen bonds in our hydrophobic system can facilitate the
formation of oxazolidinones. Even transient interactions could
have significant effects, however, as observed experimentally.
Studies are in progress aimed at ascertaining the influence of
hydrogen bonds and of other factors on the size and tightness
of the molecular assembly involved and its reactivity.
Synthesis of substituted guanidines
Alkylureas (1,1,3,3-tetraoctylurea and 1,3-diisopropylurea)
were prepared from triphosgene and the respective amine,
adapting literature13 methods. Thus triphosgene (2.0 g, 7 mmol)
and dry dichloromethane (20 ml) were charged to a 100 ml two-
necked flask and a solution of ethyldiisopropylamine (4.5 ml,
25 mmol) and piperidine (5.0 ml, 50 mmol) in dry dichloro-
methane (20 ml) was added slowly at room temperature under a
nitrogen atmosphere. After heating at 40 ЊC for 24 h the solvent
was removed under reduced pressure. 1,3-Dipiperidylurea was
isolated (2.7 g, 76%) as a white solid (mp 74 ЊC) by acid extrac-
tion of the basic products (Found: C, 67.2; H, 10.1; N, 14.2.
C11H20H2O requires C, 67.3; H, 10.2; N, 14.3%).
Guanidines 4b–g and 9 were also prepared by modifying the
literature procedures.14 An illustrative example is given for the
synthesis of 2-cyclohexyl-1,1,3,3-tetramethylguanidine 4e. Dry
1,2-dichloroethane (50 ml) and tetramethylurea (5.05 ml, 42
mmol) were charged to a 250 ml two-necked flask and oxalyl
chloride (8.0 ml, 92.0 mmol) was added at room temperature.
The solution was heated at 60 ЊC for 12 h, then the solvent was
removed under vacuum. The residual yellow solid was dissolved
in dry acetonitrile (30 ml), and cyclohexylamine (9.2 ml, 80.6
mmol) in dry acetonitrile (20 ml) was added dropwise at 0 ЊC.
The reaction mixture was allowed to warm to room temper-
ature and then refluxed for 24 h. After removal of the sol-
Experimental
Mps were determined on an Electrothermal melting point
apparatus and are uncorrected. Elemental analyses were carried
1544
J. Chem. Soc., Perkin Trans. 1, 1998

View Online
vent under reduced pressure the residue was treated with 30%
aqueous NaOH. The organic layer was extracted with diethyl
ether and dried with anhydrous Na2SO4. After removal of the
diethyl ether, distillation of the residue at 120 ЊC/6 mbar yielded
a colorless oil (6.5 g, 76%) (Found: C, 66.6; H, 11.6; N, 21.0.
C11H23N3 requires C, 67.0; H, 11.7; N, 21.3%).
Guanidines 4h, k, l and 8 were prepared according to a differ-
ent literature procedure.15 Thus for 1,2,3-tricyclohexyl-
guanidine 4l, 1,3-dicyclohexylcarbodiimide (4.2 g, 20 mmol)
and cyclohexylamine (4.6 g, 40 mmol) were charged with dry
tert-butyl alcohol (40 ml) in a 250 ml two-necked flask equipped
with a reflux condenser and a nitrogen inlet tube. The mixture
was stirred under a nitrogen atmosphere at 100 ЊC for 24 h.
After removal of the solvent under reduced pressure the residue
was distilled first at 90 ЊC/15 mbar to remove unconverted
cyclohexylamine then at 170 ЊC/1 mbar,† thus obtaining pure
guanidine (4.5 g, 74%) as a white solid (mp 92 ЊC) (Found: C,
74.6; H, 11.4; N, 13.7. C19H35N3 requires C, 74.8; H, 11.5; N,
13.8%). All the superbases were kept under nitrogen.
(6H, s, 2Me), 2.69 (6H, s, 2Me), 3.02 (2H, t, J 7.2, CH2); m/z 157
(Mϩ, 22%), 113 (17), 85 (76), 71 (100), 42 (29).
2-n-Octyl-1,1,3,3-tetramethylguanidine 4c. Pale yellow oil
(Found: C, 68.6; H, 12.8; N, 18.4. C13H29N3 requires C, 68.7; H,
12.8; N, 18.5%); νmax(film)/cmϪ1 2924s, 2854m, 1624s, 1447vs,
867w; δH 0.75 (3H, t, J 7.1, Me), 1.14 (10 H, br s, 5CH2), 1.34–
1.41 (2H, m, CH2), 2.52 (6H, s, 2Me), 2.61 (6H, s, 2Me), 2.98
(2H, t, J 7.3, CH2); m/z 227 (Mϩ, 23%), 198 (11), 184 (14), 168
(17), 142 (10), 100 (25), 85 (81), 71 (100).
2-n-Dodecyl-1,1,3,3-tetramethylguanidine 4d. Deliquescent
pale yellow solid (Found: C, 72.0; H, 13.0; N, 14.7. C17H37N3
requires C, 72.1; H, 13.1; N, 14.8%); νmax(film)/cmϪ1 2923vs,
2853s, 1623s, 1459s, 1358m; δH 0.87 (3H, t, J 6.9, Me), 1.24
(20H, br s, 10CH2), 2.78 (12H, br s, 4Me), 3.11 (2H, t, J 7.1,
CH2); m/z 283 (Mϩ, 5%), 239 (4), 196 (7), 184 (6), 142 (6), 115
(7), 100 (18), 85 (67), 71 (100), 43 (34).
2-Cyclohexyl-1,1,3,3-tetramethylguanidine 4e. Pale yellow oil
(Found: C, 68.8; H, 11.6; N, 21.1. C11H23N3 requires C, 67.0; H,
11.7; N, 21.3%); νmax(film)/cmϪ1 2926s, 2853m, 1620s, 1450s,
1362m, 1125w, 1013w, 868w; δH 1.19–1.48 (6H, m, 3CH2), 1.55–
1.75 (4H, m, 2CH2), 2.72 (6H, s, 2Me), 2.74 (6H, s, 2Me), 3.03–
3.12 (1H, m, CH); m/z 197 (Mϩ, 8%), 154 (10), 126 (7), 111 (11),
100 (13), 85 (23), 71 (100).
2-n-Dodecyl-1,3-diisopropylguanidine 4f. Deliquescent white
solid (Found: C, 73.2; H, 13.2; N, 13.4. C19H41N3 requires C,
73.3; H, 13.2; N, 13.5%); νmax(film)/cmϪ1 3249s, 3238s, 2945m,
2926, 2855s, 1619vs, 1468m, 1371m, 1170w; δH 0.87 (3H, t,
J 7.1, Me), 1.10 (12H, d, J 6.3, 4Me), 1.24 (20H, br s, 10CH2),
1.88, 1.92 (2H, 2 br s, 2NH), 2.98 (2H, t, J 7.1, CH2), 3.44–3.64
(2H, m, 2CH); m/z 311 (Mϩ, 9%), 296 (9), 212 (11), 200 (18),
170 (19), 156 (16), 85 (27), 58 (100), 43 (96).
2-Cyclohexyl-1,3-diisopropylguanidine 4g. Deliquescent white
solid (Found: C, 69.2; H, 12.0; N, 18.6. C13H27N3 requires C,
69.3; H, 12.0; N, 18.7%); νmax(film)/cmϪ1 3345m, 2942s, 2929vs,
2854s, 1643vs, 1499m, 1450s, 1363m, 1176m, 1125w, 889w; δH
1.07 (12H, d, J 6.4, 4Me), 1.11–1.32 (6H, m, 3CH2), 1.54–1.58,
1.66–1.71 (4H, 2 m, 2CH2), 1.81, 1.85 (2H, 2 br s, 2NH); m/z
225 (Mϩ, 5%), 210 (3), 182 (7), 110 (11), 98 (32), 85 (29), 58
(199), 43 (98).
1,2,3-Triisopropylguanidine 4h. Deliquescent pale yellow
solid (Found: C, 64.8; H, 12.4; N, 22.6. C10H23N3 requires C,
64.9; H, 12.4; N, 22.7%); νmax(film)/cmϪ1 3212w, 3174m, 3110m,
2970m, 1618s, 1443vs, 1378m, 1339w, 1169w, 867w; δH 1.10
(18H, d, J 6.4, 6Me), 1.90, 1.95 (2H, 2 br s, 2NH), 3.44–3.53
(3H, m, 3CH); m/z 185 (Mϩ, 7%), 170 (5), 128 (9), 113 (14), 85
(36), 69 (24), 58 (96), 43 (100).
1,2,3-Tricyclohexylguanidine 4k. White solid, mp 92 ЊC
(Found: C, 74.7; H, 11.5; N, 13.7. C19H35N3 requires C, 74.8; H,
11.5; N, 13.8%); νmax(KBr)/cmϪ1 3310s, 3241s, 2924vs, 2850s,
1625s, 1622vs, 1530s, 1510s, 1448s, 1249m, 889m, 723m; δH
1.11–1.37 (18H, m, 18CH), 1.56–1.61, 1.69–1.75 (12H, 2 m,
12CH), 1.83, 1.88 (2H, 2 br s, 2NH), 3.09–3.17 (3H, m, 3CH);
m/z 305 (Mϩ, 8%), 223 (5), 166 (9), 162 (7), 141 (38), 110 (21),
98 (85), 83 (24), 55 (100), 41 (65).
2-n-Dodecyl-1,3-dicyclohexylguanidine 4l. Colourless oil
(Found: C, 76.6; H, 12.4; N, 10.6. C25H49N3 requires C,
76.7; H, 12.5; N, 10.7%); νmax(film)/cmϪ1 3306m, 2925vs,
2853s, 1644s, 1501m, 1449vs, 1337m, 1148m, 889m, 720w;
δH 0.86 (3H, t, J 7.0, Me), 1.07–1.20 (6H, m, 6CH), 1.23
(18H, br s, 9CH2), 1.23–1.35 (8H, m, 8CH), 1.46–1.58 (4H, m,
4CH), 1.67–1.71 (4H, m, 4CH), 1.87, 1.89 (2H, br s, 2NH), 2.97
(2H, t, J 7.3, CH2), 3.05–3.16 (2H, m, 2CH); m/z (CI) 392
[(M ϩ 1)ϩ, 61%], 391 (Mϩ, 100), 311 (42), 310 (46), 294 (44),
207 (67).
General procedure for the synthesis of oxazolidinones from
acetylenic amines and carbon dioxide
Reactions under CO2 pressure in acetonitrile or water
Catalytic and stoichiometric carboxylations were carried out
in a 40 cm3 stainless steel autoclave (Parr) with magnetic stir-
ring. In a typical experiment the autoclave was charged under
nitrogen with the superbase and the amine in the appropriate
ratio. A fixed volume of solvent (acetonitrile) was added in
order to obtain the required concentration of the base. The
autoclave was cooled at about Ϫ10 ЊC, purged four times with
CO2, then pressurised with CO2 and heated under stirring for
the required time. Conditions are indicated in Tables 1, 2 and 3.
Reactions with water in place of acetonitrile were carried out
similarly (conditions in Table 4).
For reactions at atmospheric pressure a Schlenk glass reactor
(50 ml) with magnetic stirring was utilized. In a typical experi-
ment the reactor was charged under nitrogen with the super-
base and the amine in the appropriate ratio. A fixed volume of
water was added and CO2 was released through the reactor for
some minutes, then the mixture was heated at 70 ЊC and stirred
under an atmosphere of CO2 for 24 h. Conditions are indicated
in Table 6.
Reactions with sodium hydrogen carbonate as carbon dioxide
carrier
The reactions were carried out in a Schlenk glass reactor (50
ml) with magnetic stirring. In a typical experiment the reactor
was charged under nitrogen with the superbase, the amine,
sodium hydrogen carbonate and where indicated with NBu4Br
in the appropriate ratio. A fixed volume of acetonitrile or
water was added. The mixture was heated at 80 ЊC under stir-
ring for 15 h. Conditions are indicated in Tables 4 and 6.
Separation of the products
Pure oxazolidinones 2a–i and 3f were isolated from the reac-
tion mixture in acetonitrile by evaporating the solvent and
removing the basic compounds by acid extraction. Separation
of 2 and 3 was carried out by column chromatography on silica
gel with hexane–ethyl acetate (8:2) as eluent.
Characterization of guanidines
New guanidines were identified by elemental analysis, IR, H
1
NMR and MS data.
2-n-Propyl-1,1,3,3-tetramethylguanidine 4b. Colourless oil
(Found: C, 60.9; H, 12.0; N, 26.7. C8H19N3 requires C, 61.1; H,
12.1; N, 26.8%); νmax(film)/cmϪ1 2968m, 2938m, 1618s, 1440vs,
867m; δH 0.84 (3H, t, J 7.2, Me), 1.43–1.53 (2H, m, CH2), 2.61
N,NЈ-Dicyclohexylpiperidine-1-carboximidamide 8. White
solid, mp 40 ЊC (Found: C, 74.1; H, 11.3; N, 14.3. C18H33N3
requires C, 74.2; H, 11.3; N, 14.4%); νmax(KBr)/cmϪ1 3408m,
2927vs, 3850s, 1634vs, 1448m, 1365m, 1251m, 1115w, 1047w,
890w; δH 1.13–1.29 (12H, m, 12CH), 1.52 (6H, br s, 3CH2),
1.57–1.61, 1.71–1.75 (8H, 2 m, 4CH2), 1.89 (1H, br s, NH),
† 1 Bar = 105 Pa.
J. Chem. Soc., Perkin Trans. 1, 1998
1545

View Online
2.85–2.95 (2H, m, 2CH), 3.01–3.03 (4H, m, 2CH2); m/z 291
(Mϩ, 12%), 248 (13), 127 (58), 84 (100), 55 (45).
requires C, 64.7; H, 7.8; N, 8.4%); νmax(film)/cmϪ1 2980s, 2934m,
1776vs, 1675s, 1430m, 1400s, 1330m, 1047s, 980m, 760m; δH
1.37 (6H, s, 2Me), 3.80 (2H, ddd, J 6.0, 1.4, 1.3, CH2), 4.19 (1H,
N-Cyclohexyl-1,1-di(piperidin-1-yl)methylidenamine 9. Pale
yellow oil (Found: C, 73.5; H, 11.2; N, 151. C17H31N3 requires C,
73.6; H, 11.2; N, 15.2%); νmax(film)/cmϪ1 2927s, 2852m, 1616s,
1446vs, 1370s, 1249w, 1128w, 866w; δH 1.14–1.34 (6H, m, 3CH2)
1.50, 1.54 (12H, 2 br s, 6CH2), 1.54–1.62, 1.67–1.73 (4H, 2 m,
2CH2), 2.99–3.04 (8H, m, 4CH2), 3.13–3.18 (1H, m, CH); m/z
277 (Mϩ, 19%), 234 (18), 194 (20), 151 (22), 111 (100), 84 (84),
69 (21), 55 (40), 41 (36).
d, J 3.2, ᎐CH), 4.59 (1H, d, J 3.2, ᎐CH), 5.11 (1H, ddt, J 10.1,
᎐
᎐
1.4, 1.3, ᎐CHH), 5.20 (1H, J 17.1, 1.4, 1.3, CHH), 5.73–5.85
᎐
(1H, m, ᎐CH); δ 27.38 (2Me), 42.79 (CH ), 61.26 (qC), 83.85
᎐
C
2
(᎐CH ), 117.38 (᎐CH ), 133.55 (᎐CH), 154.80 (qC), 160.60
᎐
᎐
᎐
2
2
(qC); m/z 167 (Mϩ, 10%), 152 (100), 140 (6), 124 (5), 112 (11),
82 (10), 56 (7).
N-Benzyl-5-ethylidene-1,3-oxazolidin-2-one 2i. Pale yellow oil
(Found: C, 70.8; H, 6.3; N, 6.8. C12H13NO2 requires C, 70.9; H,
6.4; N, 6.9%); νmax(film)/cmϪ1 2923m, 2855w, 1783s, 1718s,
1646m, 1535w, 1479m, 1428m, 1208m, 1084s, 1000m, 755w, 702m;
δH 1.65 (3H, dt, J 7.1, 2.3, Me), 3.92–3.97 (2H, m, CH2), 4.43
(2H, s, CH ), 4.25–4.57 (1H, m, ᎐CH), 7.23–7.34 (5H, m, Ph);
Characterization of products
Spectroscopic data for the identification of products 2f and
3f have been reported.1 New compounds were identified by
elemental analysis, IR, 1H, 13C NMR and MS data.
N-Methyl-5-methylene-1,3-oxazolidin-2-one 2a. Colourless oil
(Found: C, 53.1; H, 6.2; N, 12.3. C5H7NO2 requires C, 53.1; H,
6.2; N, 12.4%); νmax(film)/cmϪ1 2929m, 1791vs, 1680s, 1488m,
1383m, 1245m, 954w, 876w, 756m; δH 2.85 (3H, s, Me), 4.11
᎐
2
m/z 203 (Mϩ, 18%), 188 (2), 147 (51), 112, (4), 91 (100), 65 (6).
Acknowledgements
(2H, t, J 2.5, CH ), 4.22 (1H, dt, J 2.8, 2.7, ᎐CHH), 4.64 (1H,
We thank Ministero Università, Ricerca Scientifica e Tecno-
logica (MURST) and CNR, Progetto Strategico and Progetto
Tecnologie Chimiche Innovative for financial support. The
facilities of Centro Interfacoltà di Misure of the University of
Parma have been utilized for NMR determination.
᎐
2
dt, J 2.8, 2.7, ᎐CHH); m/z 113 (Mϩ, 100%), 98 (2), 85 (10), 69 (5),
᎐
57 (20), 42 (20).
N-Butyl-5-methylene-1,3-oxazolidin-2-one 2b. Colourless oil
(Found: C, 61.8; H, 8.4; N, 8.9. C8H13NO2 requires C, 61.9; H,
8.4; N, 9.0%); νmax(film)/cmϪ1 2963m, 2932m, 2872m, 1781s,
1691m, 1473m, 1427m, 1283m, 1236w, 1115w, 1047m, 829w; δH
0.93 (3H, t, J 7.4, Me), 1.28–1.40 (2H, m, CH2), 1.48–1.58 (2H,
m, CH2), 3.29 (2H, t, J 7.3, CH2), 4.14 (2H, t, J 2.4, CH2), 4.26
References
1 M. Costa, G. P. Chiusoli and M. Rizzardi, Chem. Commun., 1996,
1699.
2 J. E. Baldwin, J. Chem. Soc., Chem. Commun., 1976, 734.
3 P. Schmidtchen, A. Gleich and A. Schummer, Pure Appl. Chem.,
1989, 61; see also for adducts with nitro alkanes: E. van Aken,
H. Wynberg and F. van Bolhuis, J. Chem. Soc., Chem. Commun.,
1992, 629.
4 S. J. Angyal and W. K. Warburton, J. Chem. Soc., 1951, 2492.
5 (a) H. K. Hall, Jr., J. Am. Chem. Soc., 1957, 79, 5441; (b) J. Phys.
Chem., 1956, 60, 63.
6 R. Schwesinger, Chimia, 1985, 39, 269; R. Schwesinger, J. Willaredt,
H. Schlemper, M. Keller, D. Schmitt and H. Fritz, Chem. Ber., 1994,
127, 2435; H. H. Karsch, T. Rupprich and M. Heckel, Chem. Ber.,
1994, 127, 959; R. Schwesinger, H. Schlemper, C. Hasenfratz,
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J. Boele, H. Fritz, D. Putzas, H. W. Rotter, F. G. Bordwell, A. V.
Satish, G. Zen Ji, E. M. Peters, K. Peters, H. G. von Schnering and
L. Walz, Liebigs Ann., 1996, 1055.
(1H, dd, J 2.4, 2.3, ᎐CH), 4.72 (1H, dd, J 2.4, 2.4, ᎐CH); δ
᎐
᎐
C
13.52 (Me), 19.74 (CH2), 29.29 (CH2), 43.51 (CH2), 47.81
(CH ), 86.17 (᎐CH ), 149.24 (᎐C), 155.52 (CO); m/z 155 (Mϩ,
᎐
᎐
2
2
23%), 126 (3), 112 (37), 84 (12), 57 (25), 41 (100).
N-Benzyl-5-methylene-1,3-oxazolidin-2-one 2c. Colourless oil
(Found: C, 68.7; H, 5.8; N, 7.3. C11H11NO2 requires C, 68.8;
H, 5.8; N, 7.4%); νmax(film)/cmϪ1 3064m, 3032m, 2925w, 1794s,
1679s, 1425m, 1282m, 1239m, 1059m, 970w, 877w, 834w; δH
4.01 (2H, t, J 2.4, CH ), 4.22 (1H, dd, J 2.9, 2.4, ᎐CH), 4.46
᎐
2
(2H, s, CH ), 4.73 (1H, dd, J 2.9, 2.4, ᎐CH), 7.04–7.19 (5H, m,
᎐
2
Ph); δC 47.27 (CH ), 86.62 (᎐CH ), 128.15 (2 ᎐CH), 128.20
᎐
᎐
2
2
(᎐CH), 128.96 (2 ᎐CH), 135.07 (qC), 149.07 (qC), 155.62 (CO);
᎐
᎐
m/z 189 (Mϩ, 5%), 91 (100), 65 (19), 51 (6).
N-Butyl-4-methyl-5-methylene-1,3-oxazolidin-2-one 2d. Col-
ourless oil (Found: C, 63.8; H, 8.8; N, 8.2. C9H15NO2 requires
C, 63.9; H, 8.9; N, 8.3%); νmax(film)/cmϪ1 2962s, 2875s, 1781vs,
1695s, 1447m, 1418m, 1379w, 1283s, 1224m, 1084s, 1034s,
958m; δH 0.92 (3H, t, J 7.3, Me), 1.26–1.37 (2H, m, CH2), 1.37
(3H, d, J 6.4, Me), 1.46–1.54 (2H, m, CH2), 3.06 (1H, dddd,
J 14.2, 8.4, 5.4, 1.4, NCHH), 3.43 (1H, dddd, J 14.2, 8.6, 7.4,
7 A. J. Kirby, Angew. Chem., Int. Ed. Engl., 1996, 35, 707 and
references therein.
8 See for example: J. Knowles, Ann. Rev. Biochem., 1989, 58, 195;
G. Schneider, in Carbon Dioxide Chemistry: Environmental Issues,
ed. J. P. Pradier and C. M. Pradier, The Royal Society of Chemistry,
Cambridge, UK, p. 150; D. N. Silverman and S. Lindkog, Acc.
Chem. Res., 1988, 21, 30; L. L. Kiefer, S. A. Paterno and C. A.
Fierke, J. Am. Chem. Soc., 1995, 117, 6831.
9 For an example of application of the concept to chemical reactions
see: D. C. Rideout and R. Breslow, J. Am. Chem. Soc., 1980, 102,
7817; R. Breslow, Acc. Chem. Res., 1991, 24, 159.
10 S. Shan and D. Herschlag, J. Am. Chem. Soc., 1996, 118, 5515.
11 See for example: R. P. Dixon, S. J. Geib and A. D. Hamilton, J. Am.
Chem. Soc., 1992, 114, 365; E. Fan, S. A. Van Arman, S. Kincaid and
A. D. Hamilton, J. Am. Chem. Soc., 1993, 115, 369.
12 L. Brandsma, Preparative Acetylenic Chemistry, Elsevier,
Amsterdam, 2nd edn., 1988.
13 Y. Imada, M. Yuosa, I. Nakamura and I. Murahashi, J. Org. Chem.,
1994, 59, 2282.
14 H. Heckert and B. Forster, Angew. Chem., Int. Ed. Engl., 1987, 26,
894; P. Majer and R. S. Randad, J. Org. Chem., 1994, 59, 1937.
15 G. Barcelo, D. Grenonillat, J. P. Senet and G. Sennyey, Tetrahedron,
1990, 46, 1839; D. H. R. Barton, J. D. Elliott and S. D. Géro,
J. Chem. Soc., Perkin Trans. 1, 1982, 2085.
1.3, NCHH), 4.22 (1H, dd, J 3.2, 2.7, ᎐CH), 4.36 (1H, qdd,
᎐
J 6.4, 2.7, 1.3, ᎐CH), 4.68 (1H, dd, J 3.2, 1.3, ᎐CH); m/z 169
᎐
᎐
(Mϩ, 10%), 154 (21), 140 (5), 125 (4), 110 (29), 82 (100), 68 (9),
54 (6).
N-Butyl-4,4-dimethyl-5-methylene-1,3-oxazolidin-2-one 2e.
Colourless oil (Found: C, 65.6; H, 9.3; N, 7.6. C10H17NO2
requires C, 65.7; H, 9.3; N, 7.7%); νmax(film)/cmϪ1 2962s,
2936s, 2875m, 1777vs, 1674s, 1444m, 1260w, 1110s, 1034s, 830m;
δH 0.90 (3H, t, J 7.3, Me), 1.27–1.31 (2H, m, CH2), 1.38 (6H, s, 2
Me), 1.53–1.59 (2H, m, CH2), 3.10 (2H, t, J 7.9, CH2), 4.18 (1H,
d, J 3.2, ᎐CHH), 4.59 (1H, d, J 3.2, ᎐CHH); m/z 183 (Mϩ, 5%),
᎐
᎐
169 (100), 154 (5), 140 (10), 126 (5), 112 (80), 98 (10).
N-Hexyl-4,4-dimethyl-5-methylene-1,3-oxazolidin-2-one 2g.
Colourless oil (Found: C, 68.1; H, 9.9; N, 6.5. C12H21NO2
requires C, 68.2; H, 10.0; N, 6.6%); νmax(film)/cmϪ1 2960s, 2932s,
2869m, 1773vs, 1675s, 1439m, 1260w, 1116s, 829m, 764m; δH
0.89 (3H, t, J 6.8, Me), 1.25–1.32 (6H, m, 3CH2), 1.41 (6H, s,
2Me), 1.58–1.62 (2H, m, CH2), 3.12 (2H, t, J 7.7, NCH2), 4.19
(1H, d, J 3.3, ᎐CH), 4.62 (1H, d, J 3.3, ᎐CH); m/z 211 (Mϩ, 6%),
16 U. Schuchardt, R. M. Vargas and G. Gelbard, J. Mol. Catal. A,
1995, 99, 65.
᎐
᎐
196 (100), 140 (14), 112 (65), 41 (21).
N-Allyl-4,4-dimethyl-5-methylene-1,3-oxazolidin-2-one
Colourless oil (Found: C, 64.6; H, 7.7; N, 8.3. C9H13NO2
Paper 8/00453F
Received 16th January 1998
Accepted 19th February 1998
2h.
1546
J. Chem. Soc., Perkin Trans. 1, 1998