Microwave-assisted solvent-free synthesis of enol carbamates

Article abstract of DOI:10.1055/s-2007-985607

An efficient and simple method for the synthesis of enol carbamates by irradiation with microwaves under solvent-free conditions has been developed. The method has been applied to substituted acetophenones, cyclic aryl ketones and α-aryl ketones. Its main advantages are short reaction times, good conversions except for nitro acetophenones, and the environmentally friendly nature of the process. For α-aryl ketones the reaction shows regioselectivity to afford conjugated products. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-985607

2420
LETTER
Microwave-Assisted Solvent-Free Synthesis of Enol Carbamates
M
icrowa
v
u
e-Assiste
d
S
l
olvent-
i
Free Sy
o
nthesis of Enol Ca
A
rbamate
s
. Seijas,* M. Pilar Vázquez-Tato,* José Crecente-Campo
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Santiago de Compostela, Aptdo 280, 27080 Lugo, Spain
Fax +34(982)285872; E-mail: qoseijas@lugo.usc.es; E-mail: pilarvt@lugo.usc.es
Received 20 June 2007
Microwave-assisted organic synthesis (MAOS) has
Abstract: An efficient and simple method for the synthesis of enol
shown to be a valuable tool for reducing reaction times,
getting cleaner reactions, improving yields, simplifying
work-up and designing energy-saving protocols. The in-
carbamates by irradiation with microwaves under solvent-free
conditions has been developed. The method has been applied to
substituted acetophenones, cyclic aryl ketones and a-aryl ketones.
Its main advantages are short reaction times, good conversions creasing demand for clean and efficient ‘eco-friendly’
except for nitro acetophenones, and the environmentally friendly
nature of the process. For a-aryl ketones the reaction shows regio-
selectivity to afford conjugated products.
chemical syntheses has focused general interest on sol-
vent-free reactions which, when combined with micro-
wave irradiation, have advantages from both economic
and environmental standpoints.20–23 Our previous experi-
Key words: solvent-free, microwave, enol carbamates
ence in MAOS24–30 led us to consider to assist the forma-
tion of 1-phenylenol carbamates from ketones and N,N-
Carbamates are derivatives of carbamic acid and find diisopropylcarbamoyl chloride by microwave irradiation.
diverse applications in agriculture. Vinyl carbamates are
On the basis of these facts, for this study acetophenone
useful as agricultural pesticides, herbicides, insecticides
was used as model compound. Therefore, acetophenone
and related products,1 and are intermediates in the prepa-
and N,N-diisopropylcarbamoyl chloride were irradiated
ration of pharmaceutical products, or, after polymeriza-
without catalyst,18 but low yields were obtained. Micro-
tion they yield interesting materials.2 Enol carbamates are
wave irradiation with acid catalysis (ZnCl2 or TsOH) in
also valuable as umpoled synthons3 due to the electro-
conditions similar to those used for the formation of enol
philic character of their b-position4 and the stabilization of
anions at the g-carbon.5 1-Aryl enol carbamate has proven
to be a useful group for carbolithiations on the enolic dou-
ble bond,4 for 1,2-Wittig rearrangements,6 and to direct
stereoselective metallations in conjunction with the chiral
base sparteine,7–11 or to obtain enantiomerically enriched
alcohols by asymmetric hydrogenation.12,13 Until now,
very few methods for their preparation have been de-
scribed; some of them require the use of ruthenium14 or
palladium15 complexes, or a-metallation.16 Other methods
based on enolization–acylation involve the deprotonation
of the ketone with lithium 2,2,6,6-tetramethylpiperidide
(LTMP) followed by acylation with a chloroformate using
HMPA17 (1-phenylvinyl N,N-diisopropylcarbamate was
obtained by this procedure13 in moderate yield of 49%),
the heating of aromatic ketones and carbamoyl chlorides
at 160 °C in the absence of a solvent (26% yield for 3,4-
dihydronaphthalen-1-yl dimethyl carbamate),18 or the
addition of pyridine as a base and solvent at 90 °C.4 This
last procedure presents the inconvenience of very long
reaction times (6–9 days) and it has been described for
only a few examples. In fact, when we tried to apply these
reaction conditions to convert 4-methoxyacetophenone
into the corresponding N,N-diisopropylcarbamate, it
failed completely.19 This led us to start searching for an
alternative method to get those compounds in a rapid and
easy way.
acetates in steroid nucleus31 was also disappointing.
Therefore, basic catalysis was tried in order to favor the
enolate formation. Thus, bases such as DABCO, DBU
and Hünig’s base, after 20 minutes of irradiation (150 °C)
under solvent-free conditions32 afforded the enol carba-
mate 2a in 53%, 37% and 54% conversions, respectively.
Pyridine, the base used in the conventional method, gave
yields below 30% for different reaction times (20–45 min)
and temperatures (125–180 °C). Pyridine derivatives were
also studied; DMAP and 2,6-dimethylpyridine rendered
20% and 49% yields of enol carbamate, while 2,4,6-colli-
dine raised the yield to 55% after 20 minutes of irradia-
tion. This last reaction was very clean and allowed for
longer reaction times. In this way the conversion was in-
creased to 68% after one hour of irradiation at 150 °C in
an open vessel;32 thus, it was quantitative when the recov-
ered starting material was considered. This result is a con-
siderable improvement compared with the previous
synthetic method (144-fold reduction in reaction time and
better yield).19 The same time and temperature conditions
and the use of a heating mantle afforded just 34% conver-
sion. Longer reaction times increased this yield slightly
but it also caused the appearance of by-products.
The scope of reaction was established for different substi-
tution patterns in the aromatic ring, varying their nature,
number and position (Scheme 1). Strong electron-donat-
ing groups such as methoxyl, isopropoxyl, benzyloxyl or
hydroxyl groups were compatible affording the corre-
sponding enolates in high grade of conversion (Table 1,
entries 2–5). In the case of the hydroxyl group an addi-
tional reaction of acylation was observed to give an O-aryl
SYNLETT 2007, No. 15, pp 2420–2424
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9
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Advanced online publication: 23.08.2007
DOI: 10.1055/s-2007-985607; Art ID: D18907ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Microwave-Assisted Solvent-Free Synthesis of Enol Carbamates
2421
O
located in position 4 (Table 1, entry 5). The decrease in
the yield must have been caused by steric hindrance from
the in situ formed carbamate in position 2. When an
alkoxy substituent was in position 3 it gave somewhat
lower yield as for 3-hydroxyacetophenone (Table 1,
entries 8 and 9), probably due to the lack of conjugation
between the enolate and the substituent in position 3.
O
iPr
iPr
O
O
N
iPr
Cl
N
iPr
R4
R4
R1
R3
R1
R3
2,4,6-collidine, MW
R2
R2
1a–s
2a–s
The effect of electron-withdrawing groups was also stud-
ied. Nitro derivatives in para and meta positions (Table 1,
entries 7 and 10) gave low yields; however, p-fluoroace-
tophenone (Table 1, entry 6) yielded the corresponding
enol carbamate in a good conversion (70%). 3,4-Disubsti-
tuted acetophenones were also studied (Table 1, entries
13–15), giving the corresponding enol carbamates in
slightly lower conversion than those with the activating
groups in the para position. Condensed polycyclic aro-
matic methyl ketone 1p was successfully transformed into
the corresponding enol carbamate (Table 1, entry 16).
Scheme 1
N,N-diisopropylcarbamate in a quantitative yield. This re-
action was very fast (5 min, 110 °C) and consumed one
molar equivalent of carbamoyl chloride (CbCl).
These gratifying results allowed us to prepare 2b which
would have been unattainable using the conventional py-
ridine method.4 Similar conversions were obtained when
the electron-donating group was in the ortho position. For
instance, enol carmabate 2k was achieved in 65% conver-
sion; however, o-hydroxyacetophenone gave 2l in only
44% yield (Table 1, entries 11 and 12). This is in contrast
with the previous case in which the hydroxyl group was
The scope of the reaction is not limited to acyclic ketones.
Thus, cyclic ketones such as indanone, tetrahydronaph-
thalenone and chromanone gave high enol carbamate
Table 1 Synthesis of Enol Carbamates
Entry
1a–s
Product
Molar ratio 1/
Conversion (%)b
R1
R2
R3
R4
CbCl/2,4,6-collidine
1
2
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
2a4
2:3:3
2:3:3
2:3:3
2:3:3
1:3:3
2:3:3
2:3:3
2:3:3
1:3:3
2:3:3
2:3:3
1:3:3
2:3:3
2:3:3
1:3:3
2:3:3
2:3:3
2:3:3
2:3:3
68 [63]c
67
OMe
OBn
Oi-Pr
OH
F
H
H
2b
3
H
H
2c
70
4
H
H
2d
66
5
H
H
2e [R1 = OCON(i-Pr)2]
69
6
H
H
2f
70
7
NO2
H
H
H
2g
25
8
OBn
OH
NO2
H
H
2h
54
9
H
H
2i [R2 = OCON(i-Pr)2]
53
10
11
12
13
14
15
16
17
18
19
H
H
2j
35
H
OBn
OH
H
2k
65
H
H
2l [R3 = OCON(i-Pr)2]
44
OMe
OBn
OH
OMe
OMe
OMe
2m
53
H
2n
60
H
2o [R1 = OCON(i-Pr)2]
63
C6H4
H
2p
66
H
H
H
H
H
H
CH2
2q33
2r4
2s
93
CH2CH2
OCH2
88
84
a Reactions were heated at 150 °C for 1 h.34
b Reaction conversion was determined by 1H NMR analysis. The crude products were contaminated only by starting ketone.35
c Isolated yield with purification by distillation (160 °C, 1 mm Hg).
Synlett 2007, No. 15, 2420–2424 © Thieme Stuttgart · New York

2422
J. A. Seijas et al.
LETTER
(8) Hoppe, D.; Kraemer, T.; Schwark, J. R.; Zschage, O. Pure
Appl. Chem. 1990, 62, 1999.
(9) Hoppe, D.; Hintze, F.; Tebben, P.; Paetow, M.; Ahrens, H.;
Schwerdtfeger, J.; Sommerfeld, P.; Haller, J.; Guarnieri, W.;
Kolczewski, S.; Hense, T.; Hoppe, I. Pure Appl. Chem.
1994, 66, 1479.
(10) Hoppe, D.; Ahrens, H.; Guarnieri, W.; Helmke, H.;
Kolczewski, S. Pure Appl. Chem. 1996, 68, 613.
(11) Hoppe, D.; Hense, T. Angew. Chem., Int. Ed. Engl. 1997, 36,
2282.
(12) Jiang, X.-B.; van den Berg, M.; Minnaard, A. J.; Feringa, B.
L.; de Vries, J. G. Tetrahedron: Asymmetry 2004, 15, 2223.
(13) Panella, L.; Feringa, B. L.; de Vries, J. G.; Minnaard, A. J.
Org. Lett. 2005, 7, 4177.
conversions (93%, 88% and 84%, respectively; Table 1,
entries 17–19) that were not dependent on the size of the
aliphatic ring or the presence of a heteroatom attached to
the b-carbon of the keto group. In this case, our method
also constitutes a great improvement on previously report-
ed ones, not only for the good yields obtained but also for
the very short reaction times (2r was synthesized in 1 h
compared to 216 h using the previously described
method).4
This procedure can also be applied to a-aryl ketones since
4-methoxyphenylacetone (1t) afforded regioselectively
the conjugated enol carbamate 2t (mixture of E- and Z-
isomer) in 91% conversion (Scheme 2).36
(14) Mahe, R.; Sasaki, Y.; Bruneau, C.; Dixneuf, P. H. J. Org.
Chem. 1989, 54, 1518.
(15) Superchi, S.; Sotomayor, N.; Miao, G.; Joseph, B.; Snieckus,
V. Tetrahedron Lett. 1996, 37, 6057.
(16) Sengupta, S.; Snieckus, V. J. Org. Chem. 1990, 55, 5680.
(17) Olofson, R. A.; Cuomo, J.; Bauman, B. A. J. Org. Chem.
1978, 43, 2073.
O
iPr
O
O
O
N
iPr
iPr
Cl
N
iPr
(18) Franko-Filipasic, B. R.; Patarcity, R. Chem. Ind. (London)
1969, 166.
2,4,6-collidine, MW
(19) It has been described that 1-phenylvinyl N,N-diisopropyl-
carbamate was obtained in 73% yield; however, we have
never been able to get yields higher than 50%, even with
longer reaction times or higher temperatures.
(20) Varma, R. S. Green Chem. 1999, 1, 43.
(21) Seijas, J. A.; Vázquez-Tato, M. P. Chem. Today 2007, 25,
20.
(22) Kidwai, M. Pure Appl. Chem. 2001, 73, 147.
(23) Varma, R. S. Pure Appl. Chem. 2001, 73, 193.
(24) Seijas, J. A.; Vázquez-Tato, M. P.; Carballido-Reboredo, M.
R. J. Org. Chem. 2005, 70, 2855.
(25) Seijas, J. A.; Vázquez-Tato, M. P.; Martínez, M. M.;
Rodríguez-Parga, J. Green Chem. 2002, 4, 390.
(26) Seijas, J. A.; Vázquez-Tato, M. P.; González-Bande, C.;
Martínez, M. M.; López-Pacios, B. Synthesis 2001, 999.
(27) Seijas, J. A.; Vázquez-Tato, M. P.; Martínez, M. M. Synlett
2001, 875.
OMe
1t
2t, 91%
OMe
Scheme 2
In summary, a fast, efficient and solvent-free procedure
for the synthesis of enol carbamates from acetophenones
or a-aryl ketones and N,N-diisopropylcarbamoyl chloride
is presented. This method employs the pyridine derivative
2,4,6-collidine to favor enolate formation. The method is
more competitive than previous ones, since it leads to
better yields, requires noticeably shorter reaction times, is
easy to handle, and is also valid for cyclic and acyclic
ketones.
(28) Seijas, J. A.; Vázquez-Tato, M. P.; Martínez, M. M.
Tetrahedron Lett. 2000, 41, 2215.
Acknowledgment
(29) Seijas, J. A.; Vázquez-Tato, M. P.; Martínez, M. M.; Núñez-
Corredoira, G. J. Chem. Res., Synop. 1999, 420.
(30) Vázquez-Tato, M. P. Synlett 1993, 506.
(31) Marwah, P.; Marwah, A.; Lardy, H. A. Tetrahedron 2003,
59, 2273.
We are grateful to Xunta de Galicia for financial support
(PGIDIT05PXIB26201PR, PR405 A 098/59-0). We would also
like to thank USC for a predoctoral fellowship to J.C.C., and Dr.
Jo Dee Anderson for her linguistic support.
(32) Longer reaction times did not improve the yield
significantly.
(33) Heinl, T.; Retzzow, S.; Hoppe, D.; Fraenkel, G.; Chow, A.
Chem. Eur. J. 1999, 5, 3464.
References and Notes
(1) Khur, R. J.; Dorough, H. W. Carbamate Insecticides:
Chemistry, Biochemistry and Toxicology; CRC Press:
Cleveland, 1976.
(2) Bambury, R. E.; Seelye, D. E. Eur. Patent, EP 0396364,
1990; Chem. Abstr. 1991, 114, 254062.
(3) In Umpoled Synthons; Hase, T. A., Ed.; Wiley-Interscience:
New York, 1987, 87.
(4) Peters, J. G.; Seppi, M.; Fröhlich, R.; Wibbeling, B.; Hoppe,
D. Synthesis 2002, 381.
(5) Seppi, M.; Kalkofen, R.; Reupohl, J.; Fröhlich, R.; Hoppe,
D. Angew. Chem. Int. Ed. 2004, 43, 1423.
(6) Superchi, S.; Sotomayor, N.; Miao, G.; Joseph, B.;
Campbell, M. G.; Snieckus, V. Tetrahedron Lett. 1996, 37,
6061.
(34) General Procedure for the Synthesis of 1-Arylalkenyl
N,N-Diisopropylcarbamates 2; Synthesis of 1-Phenyl-
vinyl N,N-Diisopropylcarbamate (2a): A stirred mixture
of acetophenone (1a) (120 mg, 1 mmol), N,N-diisopropyl-
carbamoyl chloride (163 mg, 1.5 mmol) and 2,4,6-collidine
(121 mg, 1.5 mmol) was irradiated in an open vessel with
microwaves in a monomode oven (Discover CEM, 50 W and
temperature control set at 150 °C measured with an IR
sensor) for 60 min. The crude was dissolved in CH2Cl2 (30
mL) and washed with 10% aq HCl (2 × 20 mL), dried
(Na2SO4) and evaporated to give 1-phenylvinyl N,N-diiso-
propylcarbamate (2a). Further purification by distillation
(160 °C, 1 mm Hg) gave 155 mg (63%) of 2a; mp 61–63 °C
(hexane), lit.13 mp 60–62 °C.
(7) Chedid, R. B.; Fröhlich, R.; Hoppe, D. Org. Lett. 2006, 8,
3061.
Synlett 2007, No. 15, 2420–2424 © Thieme Stuttgart · New York

LETTER
Microwave-Assisted Solvent-Free Synthesis of Enol Carbamates
2423
(35) Enol carbamates and parent ketones show very similar Rf
values, making it very difficult to separate them by
chromatography. When purification by distillation is not
possible, a very easy way to remove the starting material is
to reduce it to the corresponding alcohol with sodium
borohydride followed by column chromatography. This very
method must also have been used in previously described
literature procedures as we confirmed in our laboratory.
(36) Data of previously undescribed compounds:
1-(4-Nitrophenyl)vinyl N,N-Diisopropylcarbamate (2g):
mp 83–86 °C. 1H NMR (300 MHz, CDCl3): d = 1.26–1.35
[m, 12 H, 2 × CH(CH3)2], 4.01 [sept, J = 6.6 Hz, 2 H, 2 ×
CH(CH3)2], 5.19 (d, J = 2.2 Hz, 1 H, C=CH2), 5.56 (d, J =
2.2 Hz, 1 H, C=CH2), 7.60 (d, J = 9.2 Hz, 2 H, ArH), 8.20 (d,
J = 8.8 Hz, 2 H, ArH). 13C NMR (75 MHz, CDCl3): d = 20.6,
21.8, 46.6, 47.1, 105.5, 124.1, 125.9, 142.0, 147.9, 151.9,
153.1. MS (EI): m/z (%) = 292 (1) [M+], 165 (28), 128 (94),
86 (100). IR (KBr, film): 2971, 1709, 1519, 1345, 1262
cm–1. Anal. Calcd for C15H20N2O4: C, 61.63; H, 6.90; N,
9.58. Found: C, 61.34; H, 6.41; N, 9.62.
1-(4-Methoxyphenyl)vinyl N,N-Diisopropylcarbamate
(2b): Oil. 1H NMR (300 MHz, CDCl3): d = 1.28–1.32 [m, 12
H, 2 × CH(CH3)2], 3.80 (s, 3 H, OMe), 3.99–4.03 [m, 2 H,
2 × CH(CH3)2], 4.87 (d, J = 1.8 Hz, 1 H, C=CH2), 5.28 (d,
J = 1.8 Hz, 1 H, C=CH2), 6.87 (d, J = 8.8 Hz, 2 H, ArH), 7.41
(d, J = 8.8 Hz, 2 H, ArH). 13C NMR (75 MHz, CDCl3): d =
20.7, 21.8, 46.4, 46.8, 55.5, 99.7, 114.0, 126.5, 128.4, 153.5,
153.7, 160.1. MS (EI): m/z (%) = 278 (9) [M+ + 1], 277 (22)
[M+], 135 (45), 128 (100). IR (KBr, film): 1713, 1512, 1252,
1041, 837 cm–1. Anal. Calcd for C16H23NO3: C, 69.29; H,
8.36; N, 5.05. Found: C, 68.95; H, 8.76; N, 4.72.
1-(4-Benzyloxyphenyl)vinyl N,N-Diisopropylcarbamate
(2c): mp 94–95 °C (hexane). 1H NMR (300 MHz, CDCl3):
d = 1.24–1.33 [m, 12 H, 2 × CH(CH3)2], 4.02 [br s, 2 H, 2 ×
CH(CH3)2], 4.90 (d, J = 1.8 Hz, 1 H, C=CH2), 5.07 (s, 2 H,
OCH2Ph), 5.30 (d, J = 1.8 Hz, 1 H, C=CH2), 6.93 (d, J = 8.8
Hz, 2 H, ArH), 7.32–7.42 (m, 7 H, ArH). 13C NMR (75 MHz,
CDCl3): d = 20.7, 20.8, 46.4, 46.9, 70.3, 99.8, 115.0, 126.6,
127.7, 128.2, 128.6, 128.8, 137.1, 153.5, 153.7, 159.4. MS
(EI): m/z (%) = 353 (50) [M+], 128 (100). IR (KBr, film):
1705, 1246, 1215, 1011, 841 cm–1. Anal. Calcd for
C22H27NO3: C, 74.76; H, 7.70; N, 3.96. Found: C, 75.12; H,
8.07; N, 3.91.
1-(4-Isopropoxyphenyl)vinylN,N-Diisopropylcarbamate
(2d): Oil. 1H NMR (300 MHz, CDCl3): d = 1.29–1.33 [m, 18
H, 3 × CH(CH3)2], 4.01 [sept, J = 6.8 Hz, 2 H, 2 ×
CH(CH3)2], 4.54 [sept, J = 6.0 Hz, 1 H, CH(CH3)2], 4.86 (d,
J = 2.2 Hz, 1 H, C=CH2), 5.27 (d, J = 1.8 Hz, 1 H, C=CH2),
6.8 (d, J = 8.8 Hz, 2 H, ArH), 7.39 (d, J = 8.8 Hz, 2 H, ArH).
13C NMR (75 MHz, CDCl3): d = 20.7, 21.8, 22.2, 46.3, 46.8,
70.1, 99.5, 115.7, 115.9, 126.5, 153.6, 153.7, 158.5. MS
(EI): m/z (%) = 305 (8) [M+], 128 (100), 86 (36). IR (KBr,
film): 2975, 1712, 1509, 1248 cm–1. Anal. Calcd for
C18H27NO3: C, 70.79; H, 8.91; N, 4.59. Found: C, 71.07; H,
8.94; N, 4.76.
1-(3-Benzyloxyphenyl)vinyl Diisopropylcarbamate (2h):
Oil. 1H NMR (300 MHz, CDCl3): d = 1.29–1.34 [m, 12 H,
2 × CH(CH3)2], 4.03 [sept, J = 6.8 Hz, 2 H, 2 × CH(CH3)2],
5.00 (d, J = 1.8 Hz, 1 H, C=CH2), 5.07 (s, 2 H, OCH2Ph),
5.40 (d, J = 1.8 Hz, 1 H, C=CH2), 6.93 (br d, J = 7.9 Hz, 1 H,
ArH), 7.10 (m, 2 H, ArH), 7.26 (t, J = 7.9 Hz, 1 H, ArH),
7.30–7.45 (m, 5 H, ArH). 13C NMR (75 MHz, CDCl3): d =
20.7, 21.8, 46.5, 46.9, 70.3, 101.9, 111.8, 115.5, 118.0,
127.7, 128.2, 128.8, 129.7, 137.1, 137.2, 153.5, 159.1. MS
(EI): m/z (%) = 353 (2) [M+], 128 (100), 91 (30). IR (KBr,
film): 2969, 1712, 1431, 1264, 1042 cm–1. Anal. Calcd for
C22H27NO3: C, 74.76; H, 7.70; N, 3.96. Found: C, 74.38; H,
7.24; N, 3.38.
1-(3-{[(Diisopropylamino)carbonyl]oxy}phenyl)vinyl
N,N-Diisopropylcarbamate (2i): mp 74–77 °C. 1H NMR
(300 MHz, CDCl3): d = 1.29 [m, 24 H, 4 × CH(CH3)2], 4.00
[br s, 4 H, 4 × CH(CH3)2], 5.00 (d, J = 1.8 Hz, 1 H,
CH=CH2), 5.41 (d, J = 2.2 Hz, 1 H, CH=CH2), 7.08 (dt, J =
2.2, 7.0 Hz, 1 H, ArH), 7.20 (m, 1 H, ArH), 7.28–7.34 (m, 2
H, ArH). 13C NMR (75 MHz, CDCl3): d = 20.7, 21.7, 46.6,
102.2, 118.7, 121.7, 122.3, 129.4, 137.1, 151.7, 153.0. MS
(EI): m/z (%) = 390 (18) [M+], 128 (100). IR (KBr, film):
1712, 1427, 1257, 1198, 1153 cm–1. Anal. Calcd for
C22H34N2O4: C, 67.66; H, 8.78; N, 7.17. Found: C, 67.57; H,
8.42; N, 7.68.
1-(3-Nitrophenyl)vinyl N,N-Diisopropylcarbamate (2j):
mp 85–89 °C. 1H NMR (300 MHz, CDCl3): d = 1.27–1.39
[m, 12 H, 2 × CH(CH3)2], 4.02 [br s, 2 H, 2 × CH(CH3)2],
5.17 (d, J = 2.6 Hz, 1 H, C=CH2), 5.54 (d, J = 2.2 Hz, 1 H,
C=CH2), 7.52 (t, J = 8.1 Hz, 1 H, ArH), 7.81 (ddd, J = 0.8,
1.7, 7.9 Hz, 1 H, ArH), 8.16 (ddd, J = 1.4, 2.2, 8.2 Hz, 1 H,
ArH), 8.30 (t, J = 2.0 Hz, 1 H, ArH). 13C NMR (75 MHz,
CDCl3): d = 20.6, 21.7, 46.7, 47.1, 104.1, 120.0, 123.4,
129.7, 130.9, 137.6, 148.7, 151.6, 153.1. MS (EI): m/z (%) =
292 (2) [M+], 165 (40), 128 (100), 86 (32). IR (KBr, film):
2975, 1713, 1532, 1350, 1255, 1042 cm–1. Anal. Calcd for
C15H20N2O4: C, 61.63; H, 6.90; N, 9.58. Found: C, 61.36; H,
7.15; N, 9.34.
1-(2-Benzyloxyphenyl)vinyl N,N-Diisopropylcarbamate
(2k): mp 38–40 °C. 1H NMR (300 MHz, CDCl3): d = 1.25
[d, J = 6.6 Hz, 12 H, 2 × CH(CH3)2], 3.97 [sept, J = 6.6 Hz,
2 H, 2 × CH(CH3)2], 5.16 (m, 3 H, C=CH2, OCH2Ph), 5.60
(d, J = 0.9 Hz, 1 H, C=CH2), 6.93–6.98 (m, 2 H, ArH), 7.20–
7.46 (m, 7 H, ArH). 13C NMR (75 MHz, CDCl3): d = 20.7,
21.7, 46.3, 46.7, 70.7, 106.5, 113.2, 121.0, 125.2, 127.5,
128.0, 128.7, 129.6, 137.2, 150.5, 153.8, 156.4. MS (EI):
m/z (%) = 353 (40) [M+], 128 (100) [Cb], 91 (23). IR (KBr,
film): 2969, 1710 (C=O), 1446, 1289, 1240 (CO), 1043, 754
cm–1. Anal. Calcd for C22H27NO3: C, 74.76; H, 7.70; N, 3.96.
Found: C, 74.76; H, 7.43; N, 3.87.
1-(4-{[(Diisopropylamino)carbonyl]oxy}phenyl)vinyl
N,N-Diisopropylcarbamate (2e): mp 59–61 °C. 1H NMR
(300 MHz, CDCl3): d = 1.30 [m, 24 H, 4 × CH(CH3)2], 4.00
[hept, J = 6.6 Hz, 4 H, 4 × CH(CH3)2], 4.95 (d, J = 2.2 Hz, 1
H, CH=CH2), 5.33 (d, J = 2.2 Hz, 1 H, CH=CH2), 7.10 (d,
J = 8.8 Hz, 2 H, ArH), 7.46 (d, J = 8.8 Hz, 2 H, ArH). 13
C
NMR (75 MHz, CDCl3): d = 20.7, 21.6, 21.8, 46.4, 46.8,
101.2, 121.9, 126.2, 132.6, 151.9, 153.2, 153.5, 153.8. MS
(EI): m/z (%) = 390 (4) [M+], 128 (100), 86 (44). IR (KBr,
film): 1715, 1315, 1258, 1214, 1154 cm–1. Anal. Calcd for
C22H34N2O4: C, 67.66; H, 8.78; N, 7.17. Found: C, 67.36; H,
8.89; N, 7.05.
1-(4-Fluorophenyl)vinylN,N-Diisopropylcarbamate(2f):
Oil. 1H NMR (300 MHz, CDCl3): d = 1.25–1.33 [m, 12 H,
2 × CH(CH3)2], 4.00 [sept, J = 6.6 Hz, 2 H, 2 × CH(CH3)2],
4.96 (d, J = 2.2 Hz, 1 H, C=CH2), 5.33 (d, J = 2.2 Hz, 1 H,
C=CH2), 7.02 (t, J = 8.8 Hz, 2 H, ArH), 7.44 (dd, J = 5.3, 9.0
Hz, 2 H, ArH). 13C NMR (75 MHz, CDCl3): d = 20.7, 21.8,
47.0, 101.4, 115.6 (d, 2JCF = 22 Hz), 127.0, 131.9, 152.9,
153.5, 163.1 (d, 1JCF = 248 Hz). MS (EI): m/z (%) = 265 (5)
[M+], 128 (68), 86 (100). IR (KBr, film): 2968, 1712, 1510,
1259, 1214, 1043 cm–1. Anal. Calcd for C15H20FNO2: C,
67.90; H, 7.60; N, 5.28. Found: C, 68.07; H, 7.47; N, 5.19.
1-(2-{[(Diisopropylamino)carbonyl]oxy}phenyl)vinyl
N,N-Diisopropylcarbamate (2l): Oil. 1H NMR (300 MHz,
CDCl3): d = 1.23–1.32 [m, 24 H, 4 × CH(CH3)2], 3.91 [br s,
3 H, 3 × CH(CH3)2], 4.18 [br s, 1 H, CH(CH3)2], 5.15 (s, 1
H, C=CH2), 5.18 (s, 1 H, CH=CH2), 7.09 (d, J = 7.9 Hz, 1 H,
ArH), 7.16 (t, J = 7.5 Hz, 1 H, ArH), 7.29 (t, J = 7.7 Hz, 1 H,
Synlett 2007, No. 15, 2420–2424 © Thieme Stuttgart · New York

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J. A. Seijas et al.
LETTER
ArH), 7.79–7.82 (m, 3 H, ArH), 7.90 (d, J = 1.7 Hz, 1 H,
ArH), 7.42 (d, J = 7.9 Hz, 1 H, ArH). 13C NMR (75 MHz,
CDCl3): d = 20.7, 21.7, 46.7, 46.9, 105.4, 123.6, 125.1,
129.3, 129.4, 129.6, 149.0, 149.8, 153.4, 153.5. MS (EI):
m/z (%) = 391 (5) [M+ + 1], 390 (1) [M+], 128 (100), 86 (81).
IR (KBr, film): 2970, 1715, 1316, 1207, 1042 cm–1. Anal.
Calcd for C22H34N2O4: C, 67.66; H, 8.78; N, 7.17. Found: C,
67.22; H, 9.21; N, 6.95.
1-(3,4-Dimethoxyphenyl)vinyl N,N-Diisopropyl-
carbamate (2m): Oil. 1H NMR (300 MHz, CDCl3): d =
1.26–1.32 [m, 12 H, 2 × CH(CH3)2], 3.86 (s, 6 H, 2 × OMe),
4.01 [sept, J = 6.6 Hz, 2 H, 2 × CH(CH3)2], 4.89 (d, J = 1.8
Hz, 1 H, C=CH2), 5.28 (d, J = 1.8 Hz, 1 H, C=CH2), 6.81 (d,
J = 8.4 Hz, 1 H, ArH), 6.98 (d, J = 1.8 Hz, 1 H, ArH), 7.04
(dd, J = 2.2, 8.3 Hz, 1 H, ArH). 13C NMR (75 MHz, CDCl3):
d = 20.7, 21.8, 46.4, 46.8, 55.9, 56.1, 100.0, 108.4, 111.2,
118.0, 128.6, 148.9, 149.7, 153.4, 153.5. MS (EI): m/z (%) =
307 (7) [M+], 180 (13), 128 (100), 86 (65). IR (KBr, film):
1712, 1516, 1265, 1221, 1143 cm–1. Anal. Calcd for
C17H25NO4: C, 66.43; H, 8.20; N, 4.56. Found: C, 66.41; H,
7.79; N, 4.63.
1-(4-Benzyloxy-3-methoxyphenyl)vinyl N,N-Diiso-
propylcarbamate (2n): mp 75–77 °C. 1H NMR (300 MHz,
CDCl3): d = 1.26–1.33 [m, 12 H, 2 × CH(CH3)2], 3.89 (s, 3
H, OMe), 4.02 [m, 2 H, 2 × CH(CH3)2], 4.90 (d, J = 1.8 Hz,
1 H, C=CH2), 5.16 (s, 2 H, OCH2Ph), 5.30 (d, J = 2.2 Hz, 1
H, C=CH2), 6.84 (d, J = 8.4 Hz, 1 H, ArH), 6.98–7.03 (m, 2
H, ArH), 7.25–7.44 (m, 5 H, ArH). 13C NMR (75 MHz,
CDCl3): d = 20.8, 21.8, 46.4, 46.9, 56.1, 71.2, 100.2, 109.0,
113.9, 117.9, 127.4, 128.1, 128.8, 129.1, 137.2, 148.9,
149.6, 153.4, 153.6. MS (EI): m/z (%) = 383 (5) [M+], 128
(100), 91 (94), 86 (66). IR (KBr, film): 1712, 1520, 1272,
1222, 1147, 1020 cm–1. Anal. Calcd for C23H29NO4: C,
72.04; H, 7.62; N, 3.65. Found: C, 71.95; H, 7.93; N, 3.60.
1-(4-{[(Diisopropylamino)carbonyl]oxy}-3-methoxy-
phenyl)vinyl N,N-Diisopropylcarbamate (2o): Oil. 1H
NMR (300 MHz, CDCl3): d = 1.30 [m, 24 H, 4 × CH(CH3)2],
3.80 (s, 3 H, OMe), 4.00 [sept, J = 6.4 Hz, 4 H, 4 ×
CH(CH3)2], 4.96 (s, 1 H, CH=CH2), 5.32 (s, 1 H, CH=CH2),
7.03–7.05 (m, 3 H, ArH). 13C NMR (75 MHz, CDCl3): d =
20.3, 20.7, 21.6, 46.8, 56.0, 101.3, 109.6, 117.8, 123.4,
133.8, 135.3, 141.3, 151.7, 153.3. MS (EI): m/z (%) = 420
(2) [M+], 293 (1), 128 (100), 86 (44). IR (KBr, film): 1716,
1316, 1281, 1267, 1204, 1154, 1126 cm–1. Anal. Calcd for
C23H36N2O5: C, 65.69; H, 8.63; N, 6.66. Found: C, 65.63; H,
8.74; N, 6.54.
ArH). 13C NMR (75 MHz, CDCl3): d = 20.7, 21.8, 46.5,
46.9, 102.1, 123.2, 124.3, 126.5, 126.6, 127.8, 128.4, 128.7,
133.0, 133.4, 133.6, 153.6, 153.7. MS (EI): m/z (%) = 298
(11) [M+ + 1], 297 (42) [M+], 170 (39), 128 (90), 86 (100).
IR (KBr, film): 2968, 1707 (C=O), 1645, 1429, 1323, 1265,
1041, 864, 760 cm–1. Anal. Calcd for C19H23NO2: C, 76.73;
H, 7.80; N, 4.71. Found: C, 77.11; H, 7.47; N, 5.13.
1H-Inden-3-yl N,N-Diisopropylcarbamate (2q):33 Oil. 1H
NMR (300 MHz, CDCl3): d = 1.31 [d, J = 7.0 Hz, 12 H, 2 ×
CH(CH3)2], 3.62 (s, 2 H, CH2), 3.90 [br s, 1 H, CH(CH3)2],
4.11 [br s, 1 H, CH(CH3)2], 6.53 (s, 1 H, CHCH2), 7.12 (td,
J = 1.8, 7.0 Hz, 1 H, ArH), 7.20–7.29 (m, 2 H, ArH), 7.32 (d,
J = 7.2, 1 H, ArH). 13C NMR (75 MHz, CDCl3): d = 20.7,
21.8, 38.3, 46.4, 47.1, 113.3, 120.7, 123.5, 124.0, 126.8,
137.6, 143.7, 152.8, 156.8. MS (EI): m/z (%) = 260 (2)
[M+ + 1], 132 (54), 128 (84), 86 (100). IR (KBr, film): 2970,
1711, 1606, 1272, 1132, 748, 715 cm–1.
2H-Chromen-4-yl N,N-Diisopropylcarbamate (2s): mp
74.1–77.4 °C (hexane). 1H NMR (300 MHz, CDCl3): d =
1.30–1.32 [m, 12 H, 2 × CH(CH3)2], 4.02 [sept, J = 6.8 Hz,
2 H, 2 × CH(CH3)2], 4.96 (d, J = 3.5 Hz, 2 H, CH2O), 5.49
(t, J = 3.7 Hz, 1 H, C=CHCH2), 6.79 (dd, J = 0.9, 8.0 Hz, 1
H, ArH), 6.87 (td, J = 0.9, 7.5 Hz, 1 H, ArH), 7.06 (dd, J =
1.6, 7.7 Hz, 1 H, ArH), 7.13 (td, J = 1.6, 7.9 Hz, 1 H, ArH).
13C NMR (75 MHz, CDCl3): d = 20.7, 21.7, 46.7, 47.0, 65.7,
108.0, 116.1, 120.5, 121.3, 121.9, 130.0, 143.4, 152.9,
155.4. MS (EI): m/z (%) = 276 (4) [M+ + 1], 275 (19) [M+],
147 (69), 128 (83), 86 (100). IR (KBr, film): 2970, 1716
(C=O), 1306, 1207, 755 cm–1. Anal. Calcd for C16H21NO3:
C, 69.79; H, 7.69; N, 5.09. Found: C, 69.89; H, 8.05; N, 5.06.
1-(4-Methoxyphenyl)prop-1-en-2-yl N,N-Diisopropyl-
carbamate (2t); mixture of E- and Z-isomers (2:1): oil. 1H
NMR (300 MHz, CDCl3): d = 1.22–1.26 [m, 12 H, 2 ×
CH(CH3)2], 2.04 (d, J = 0.9 Hz, 3 H, Me, E-isomer), 2.09 (d,
J = 0.9 Hz, 3 H, Me, Z-isomer), 3.73 (s, 3 H, OMe, E-
isomer), 3.75 (s, 3 H, OMe, Z-isomer), 3.85–4.00 [m, 2 H,
2 × CH(CH3)2], 5.83 (s, 1 H, C=CH, E-isomer), 6.19 (s, 1 H,
C=CH, Z-isomer), 6.77 (d, J = 8.8 Hz, 2 H, ArH, E-isomer),
6.83 (d, J = 8.8 Hz, 2 H, ArH, Z-isomer), 7.18 (d, J = 8.4 Hz,
2 H, ArH, Z-isomer), 7.26 (d, J = 8.8 Hz, 2 H, ArH, E-
isomer). 13C NMR (75 MHz, CDCl3): d = 17.7, 20.8, 21.1,
21.7, 46.6, 55.3, 113.7, 113.9, 115.7, 117.7, 127.9, 128.2,
129.5, 130.1, 145.2, 147.2, 152.7, 154.1, 158.5. MS (EI):
m/z (%) = 292 (6) [M+ + 1], 291 (16) [M+], 164 (27), 163
(23), 135 (29), 128 (90), 121 (43), 86 (100). IR (KBr, film):
2970, 1707, 1512, 1252, 1041, 837, 757 cm–1. Anal. Calcd
for C17H25NO3: C, 70.07; H, 8.65; N, 4.81. Found: C, 70.55;
H, 8.74; N, 4.79.
1-(2-Naphthyl)vinyl N,N-Diisopropylcarbamate (2p): mp
58–59 °C. 1H NMR (300 MHz, CDCl3): d = 1.26–1.40 [m,
12 H, 2 × CH(CH3)2], 4.07 [m, 2 H, 2 × CH(CH3)2], 5.09 (d,
J = 2.0 Hz, 1 H, C=CH2), 5.55 (d, J = 2.0 Hz, 1 H, C=CH2),
7.44–7.48 (m, 2 H, ArH), 7.63 (dd, J = 1.8, 8.8 Hz, 1 H,
Synlett 2007, No. 15, 2420–2424 © Thieme Stuttgart · New York

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