Diels-Alder reaction of fused pyran-2-ones with ethyl vinyl ether

Article abstract of DOI:10.1007/s00706-012-0734-4

Ethyl vinyl ether was found to be an appropriate synthetic equivalent of acetylene for a set of Diels-Alder reactions with fused pyran-2-ones that yield fused carbocyclic systems. Transformations were conducted under microwave irradiation with DABCO (as a catalyst for the elimination of ethanol) and with n-butanol as the additive. A single-crystal X-ray diffraction structure is presented for N-(5,6,7,8-tetrahydro-6-methyl-8-oxonaphthalen-2-yl)benzamide. Springer-Verlag 2012.

Full text of DOI:10.1007/s00706-012-0734-4

Monatsh Chem (2012) 143:771–777
DOI 10.1007/s00706-012-0734-4
ORIGINAL PAPER
Diels–Alder reaction of fused pyran-2-ones with ethyl vinyl ether
•
Amadej Juranovic Kristof Kranjc
•
ˇ
ˇ
Slovenko Polanc Franc Perdih Marijan Kocevar
•
•
ˇ
Received: 2 November 2011 / Accepted: 6 February 2012 / Published online: 1 March 2012
Ó Springer-Verlag 2012
Abstract Ethyl vinyl ether was found to be an appro-
priate synthetic equivalent of acetylene for a set of
Diels–Alder reactions with fused pyran-2-ones that yield
fused carbocyclic systems. Transformations were con-
ducted under microwave irradiation with DABCO (as a
catalyst for the elimination of ethanol) and with n-butanol
as the additive. A single-crystal X-ray diffraction structure
is presented for N-(5,6,7,8-tetrahydro-6-methyl-8-oxo-
naphthalen-2-yl)benzamide.
the pyran-2-one scaffold is not usually stable under ther-
mal reaction conditions, and eliminates CO2 via a retro-
Diels–Alder reaction, forming a new cyclohexadiene
system that can either act as a new diene for a new Diels–
Alder reaction or alternatively (when appropriate groups
for elimination are present) aromatize into a benzene
system.
Sometimes it is desirable to replace the CO2 fragment of
the 2H-pyran-2-one ring with a CH=CH fragment. This
could be—at least theoretically—executed via the cyclo-
addition of acetylene, but such a pathway is of limited
practical synthetic utility since acetylene is very unreactive
in Diels–Alder reactions (besides being gaseous under
normal conditions, thus further limiting its use) [19].
Therefore, we and other groups have been searching for
synthetic equivalents of acetylene, and have identi-
fied ethyl vinyl ether, vinyl acetate, vinyl propionate,
cyclohexyl vinyl ether, 1-vinyl-2-pyrrolidone, and N-vi-
nylcaprolactam as possible candidates [20–32]. Even
though some cyclohexadiene intermediates can be isolated
and even characterized [32, 33], they are generally rather
unstable [34]. However, it was shown that organic bases
(such as DABCO) act as catalysts for the last reaction step
in the aromatization of a cyclohexadiene intermediate
(whereas they do not influence the preceding two steps:
cycloaddition and elimination of CO2) [31, 32].
Keywords Cycloadditions Á X-ray structure
determination Á Microwave-assisted synthesis Á
Catalysis Á Carbocycles Á Synthetic equivalent
Introduction
2H-Pyran-2-ones and their fused derivatives are well
known as appropriate dienes for a variety of Diels–Alder
reactions [1–3]. Besides alkynes [4–11], alkenes [12–18]
can also be used as dienophiles in Diels–Alder reactions:
the CO2-bridged cycloadduct (7-oxabicyclo[2.2.2]octene)
that is formed in the first reaction step when the diene is
ˇ
A. Juranovic Á K. Kranjc Á S. Polanc Á F. Perdih (&) Á
The abovementioned dienophiles containing a vinyl
moiety were indeed found to be appropriate for cycload-
ditions with substituted 3-acylamino-2H-pyran-2-ones, but
so far there have been no studies utilizing fused pyran-2-
ones. Our goal was therefore to investigate the possibilities
offered by such fused compounds, as their cycloadducts
would be similar to some biological frameworks, including
a class of known agonists of 5-hydroxytryptamine recep-
tors 1B (5-HT1B).
ˇ
M. Kocevar (&)
Faculty of Chemistry and Chemical Technology,
ˇ ˇ
University of Ljubljana, Askerceva 5,
1000 Ljubljana, Slovenia
e-mail: franc.perdih@fkkt.uni-lj.si
ˇ
M. Kocevar
e-mail: marijan.kocevar@fkkt.uni-lj.si
F. Perdih
CO EN-FIST, Dunajska cesta 156, 1000 Ljubljana, Slovenia
123

ˇ
A. Juranovic et al.
772
Scheme 1
R2
R1
OEt
R2
R1
( )n
O
O
O
- CO2
( )n
O
2
X
DABCO
n-BuOH
MW
OEt
X
NHCOPh
1
NHCOPh
3
X = CO, CH2; n = 0-3; R1, R2 = H, Me
R2
OEt
R2
R1
( )n
R1
( )n
- EtOH
X
NHCOPh
X
NHCOPh
4
5
Table 1 Reaction conditions and yields for the microwave-assisted
synthesis of 5 with ethyl vinyl ether (2) starting from 1
Results and discussion
Diels–Alder reactions between a set of fused pyran-2-ones
1 [35–37] and ethyl vinyl ether (2; see Scheme 1) were
initially conducted in closed vessels (10 cm3) under
microwave irradiation [38–46] at 120 °C, with the addition
of DABCO as the catalyst. We found that such conditions
(analogous to those used previously) [31, 32] were not
adequate to achieve quantitative conversion into the
products 5; indeed, the only way to achieve this was to
apply higher reaction temperatures (140–180 °C). How-
ever, in order to reach temperatures above 120 °C while
keeping the pressure below the upper limit [as the boiling
point of the neat ethyl vinyl ether (2) is rather low (33 °C)],
it was necessary to add some appropriate additives to
decrease the vapor pressure, such as ionic liquids (e.g.,
[bmim]BF4) or n-butanol (which, due to the easier isolation
of the products, proved to be preferable) [47–50].
Run Starting 1
Product T/°C t/mina Yield/%b
n
X
R1, R2
1
2
3
4
5
6
7
8
a
1a
1b
1c
1d
1d
1e
1f
0
1
1
1
1
0
2
3
C=O H, H
C=O H, H
C=O H, Me
5a
5b
5c
140 135
140 135
140 135
140 150
170 180
150 210
180 210
180 180
75
70
70
c
C=O Me, Me 5d
C=O Me, Me 5d
–
62d
73
70
65
CH2 H, H
CH2 H, H
CH2 H, H
5e
5f
1g
5g
Microwave irradiation in a closed vessel (10 cm3) at 300 W
Yield of isolated pure products (conversions [95%)
Conversion 43%
b
c
d
Conversion 75%
These final conditions (Table 1) were applied to syn-
thesize a set of fused carbocyclic compounds consisting of
tetrahydronaphthalene, dihydro-1H-indene, tetrahydro-5H-
5 of the fused pyran-2-one system (compare, for example,
1b with 1e–1g), whereas the presence of C=O at position 8
on the fused pyran-2-one (i.e., 1h) completely prevents
cycloaddition; no cycloadduct was detected even under
relatively severe conditions (135 min at 140 °C); see
Scheme 2. Unfortunately, harsher conditions (180 min at
180 °C) were not appropriate, as they led to the decom-
position of the reaction mixture. These results can be
explained by increased delocalization of the diene system
of the pyran-2-one ring caused by the additional carbonyl
group at position 8 bonded to the other end of the diene
fragment in 1h (as opposed to the other cases 1a–1d, where
the second carbonyl group is bonded to the central part of
the diene system, where it cannot cause such strong delo-
calization). Another effect of the carbonyl group at position
8 in 1h might also be that it decreases the polarization of
benzo[7]annulene,
and
hexahydrobenzo[8]annulene
frameworks bearing a benzoylamino group. Starting from
the fused pyran-2-ones 1 (1 mmol) and ethyl vinyl ether (2,
2 cm3) with a catalytic amount of DABCO (15 mol%,
16.8 mg) and a small amount of n-butanol (320 mg), we
obtained the products 5a–5g with good yields (65–75%).
The optimal temperatures varied between 140 and 180 °C,
and the durations required were 135–210 min, but even
these rather harsh conditions were insufficient in one case
(5d) to achieve a quantitative conversion. The pure product
5d could, however, be obtained with a suitable isolation
procedure.
It is interesting to note that the C=O group has a strongly
accelerating effect on the reaction when present at position
123

Diels–Alder reaction of fused pyran-2-ones with ethyl vinyl ether
773
OEt
O
O
X 2
O
O
NHCOPh
NHCOPh
DABCO
n-BuOH
MW
5h
1h
Scheme 2
the diene system (both ends in 1h bear carbonyl substitu-
ents), thus making the cycloaddition more like those with
neutral electron demand (which are generally known to
proceed poorly) [51].
Fig. 2 Dimer formation in 5c. Dashed lines indicate hydrogen bonds.
Disorder on C6 is omitted for clarity
Additionally, it seems that there is an inhibiting effect of
the presence of the second methyl group at position 7 of the
fused pyran-2-ones (compare 1d with 1c and 1b). Even
though both methyl groups are too far from the reacting
diene system to exert any appreciable electronic effects,
they do appear to cause certain steric interactions that
might be responsible for the lower reactivity of 1d.
In a separate experiment, 1b and 2 were treated under
conventional conditions in a closed vessel heated in an oil
bath at 140 °C for 135 min (the temperature and the
reaction time were the same as in run 2, Table 1). How-
with a small twist angle between the C1–C4/C9–C10 ring
and the phenyl ring C13–C18 of 1.82(11)°. Compound 5c
crystallizes as a centrosymmetric hydrogen-bonded dimer
facilitated by N1–H1...O2 (1-x, -y, -z) interactions
involving the amide and carbonyl groups of the tetralone
moieties of adjacent molecules (Fig. 2). The dimers can be
described by the graph-set motif R22(14) [52]. The dimeric
structure is further stabilized by additional weak C–H...O2
hydrogen bonding (Table 2). Both molecules in the dimer
1
ever, the H NMR spectrum of the crude reaction mixture
˚
are not in a plane; a separation of 0.720 A was found
did not show any signals belonging to the product 5b—
starting materials 1b and 2 remained unchanged.
between the mean planes through the C1–C4/C9–C10 rings
of the adjacent molecules.
Supramolecular aggregation is stabilized by p–p inter-
actions between two parallel C1–C4/C9–C10 rings
(centroid Cg1), with a Cg1...Cg1 (1-x, 1-y, -z) centroid-
Crystal structure of 5c
Crystals of 5c suitable for X-ray structure determination
were obtained by slow evaporation from chloroform at
room temperature. Single-crystal X-ray analysis (Fig. 1)
found substitution patterns that were in accordance with its
NMR spectral data. In the crystal structure of 5c, the mean
plane through the amide group is inclined with respect to
the C1–C4/C9–C10 ring (which is part of the tetralone
moiety) by 12.89(10)°, and to the phenyl ring C13–C18 by
14.56(12)°, leading to near-planarity of the aromatic rings,
˚
to-centroid distance of 4.0797(10) A, a perpendicular dis-
tance from the centroid Cg1 to the plane of the other ring of
˚
3.5646(7) A, and a slippage between the centroids of
˚
1.984 A. These interactions are consistent with well-
defined p–p stacking interactions [53–55], and can be
regarded as medium to strong, since strong interactions
exhibit rather short centroid–centroid contacts (CgÁÁÁCg
˚
\ 3.8 A), small slip angles (\25°), and small vertical
˚
displacements (\1.5 A), which translate into a sizeable
overlap of the aromatic planes. In comparison, medium to
weak interactions exhibit rather long centroid–centroid
˚
distances ([4.0 A), together with large slip angles ([30°)
˚
and large vertical displacements ([2.0 A) [56–59].
Supramolecular aggregation is further controlled by weak
C3–H3...Cg1 (‘-x, -‘?y, -z) hydrogen bonding
between two adjacent tetralone moieties (Fig. 3; Table 2).
Conclusions
We have shown that ethyl vinyl ether can be applied as a
useful synthetic equivalent of acetylene in Diels–Alder
reactions with a variety of dienes within fused pyran-2-one
Fig. 1 The molecular structure of 5c, showing the atom-labeling
scheme. Displacement ellipsoids are drawn at the 30% probability
level. The disorder on C6 is indicated by dashed lines
123

ˇ
A. Juranovic et al.
774
Table 2 Hydrogen bonds for 5c
˚
d(D–H)/A
˚
d(H...A)/A
˚
d(D...A)/A
D–H...A
\(DHA)/°
Symmetry transformation
for acceptors
N1–H1...O2
0.86
0.93
0.93
0.93
2.25
2.54
2.56
2.80
3.0765(19)
3.332(2)
3.420(2)
3.535(2)
162.1
143.2
153.8
137.0
1 - x, -y, -z
C10–H10...O2
C18–H18...O2
C3–H3...Cg1
1 - x, -y, -z
1 - x, -y, -z
‘ - x, -‘ ? y, -z
Cg1 is a C1–C4/C9–C10 ring centroid
spectra were recorded on the Bruker Avance DPX 300 at
75.5 MHz at 29 °C, and were referenced against the central
line of the solvent signal (CDCl3 triplet at 77.0 ppm or
DMSO-d6 septet at 39.5 ppm). The coupling constants
(J) are given in hertz. IR spectra were obtained with a Bio-
Rad (Hercules, CA, USA) FTS 3000MX spectrometer as
KBr pellets for all compounds. MS spectra were recorded
with a VG Analytical (Wythenshawe, UK) AutoSpec Q
and Waters-Micromass (Milford, MA, USA) Q-TOF Pre-
mier spectrometers. Elemental analyses (C, H, N) were
conducted using a PerkinElmer (Waltham, MA, USA)
2400 series II CHNS/O analyzer, and the results obtained
experimentally were found to be in good agreement
( 0.3%) with the calculated values. The starting com-
pounds 1 were prepared according to published procedures
[35–37]. All other reagents and solvents were used as
received from commercial suppliers.
Microwave reactions were conducted in air using a
focused microwave unit (Discover by CEM Corporation,
Matthews, NC, USA). This machine consists of a contin-
uous, focused microwave power delivery system with an
operator-selectable power output from 0 to 300 W. Reac-
tions were performed in darkness in glass vessels (capacity
10 cm3) sealed with a septum. The pressure was controlled
by a load cell connected to the vessel via the septum. The
temperature of the contents of the vessel was monitored
using a calibrated infrared temperature controller mounted
under the reaction vessel and by measuring the temperature
of the outer surface of the reaction vessel. The mixtures
were stirred with a Teflon-coated magnetic stirring bar in
the vessel. Temperature, pressure, and power profiles were
recorded using commercially available software provided
by the manufacturer of the microwave unit.
Fig. 3 Packing diagram for 5c. Dashed lines indicate p–p interac-
tions and hydrogen bonds. For the sake of clarity, H atoms not
involved in the motif shown and disorder on C6 are omitted
systems. The reactions were executed under microwave
irradiation with the addition of n-butanol (to allow the
system to be heated up to the necessary temperatures) and
DABCO (as the catalyst for the elimination of ethanol).
Additionally, a single-crystal X-ray structure of one of the
products was determined.
X-ray structure determination
Experimental
Single-crystal X-ray diffraction data were collected at
room temperature with a Bruker Nonius Kappa CCD
diffractometer using graphite monochromated Mo–Ka
radiation (k = 0.71073 A). The data were processed using
DENZO [60]. The structure was solved using direct
Melting points were determined on a micro hot stage
1
apparatus. H NMR spectra were recorded at 29 °C with a
˚
Bruker (Rheinstetten, Germany) Avance DPX 300 spec-
trometer at 300 MHz or Bruker Avance III spectrometer at
500 MHz, using TMS as an internal standard. 13C NMR
methods implemented in SHELXS-97 [61], and refined by
123

Diels–Alder reaction of fused pyran-2-ones with ethyl vinyl ether
775
Table 3 Crystallographic data for 5c
precipitated products 5a–5c, 5e, 5f were filtered off and
washed with i-Pr2O. In the case of 5d, the crude solid
remaining after the evaporation of volatile components was
separated by column chromatography on silica gel with a
mixed mobile phase of petrol ether:ethyl acetate = 7:1
which changed gradually to 3:1.
Formula
Mr
C18H17NO2
279.33
T/K
293(2)
Crystal system
Space group
Monoclinic
P 21/a
˚
a/A
15.6343(5)
5.8573(2)
16.1854(4)
100.684(3)
1,456.48(8)
4
N-(2,3-Dihydro-3-oxo-1H-inden-5-yl)benzamide
(5a, C16H13NO2)
Yield 188 mg (75%), recrystallization from ethanol. M.p.
˚
b/A
˚
c/A
1
b/°
Volume/A
205–208 °C; H NMR (300 MHz, CDCl3): d = 2.73 (m,
3
˚
2H, 1-CH2), 3.14 (m, 2H, 2-CH2), 7.50 (m, 3H, 7-H and 2H
of Ph), 7.59 (m, 1H, Ph), 7.81 (d, J = 1.8 Hz, 1H, 4-H),
7.91 (m, 2H, Ph), 8.08 (br s, 1H, NH), 8.18 (dd,
J1 = 8.5 Hz, J2 = 1.8 Hz, 1H, 6-H) ppm; 13C NMR
(75.5 MHz, CDCl3): d = 24.9, 36.3, 113.7, 127.0, 127.1,
127.6, 128.4, 131.7, 134.6, 137.0, 138.4, 150.3, 165.6,
Z
D
calc/Mg/m3
1.274
l/mm-1
0.083
F(000)
592
Crystal size/mm3
Reflections collected
Unique reflections/Rint
Parameters
R, wR2 [I [ 2r(I)]a
R, wR2 (all data)b
GOF, Sc
0.50 9 0.35 9 0.20
5,198
ꢀ
206.1 ppm; IR (KBr): m = 1,699, 1,677, 1,653, 1,639,
1,620, 1,599, 1,576, 1,542, 1,532, 1,492 cm-1; MS (ES?,
TOF): m/z = 252 (MH?); HRMS calcd for C16H14NO2
(MH?) 252.1019, found 252.1042.
3,309(0.0229)
201
0.0614, 0.1577
0.0898, 0.1786
1.042
N-(5,6,7,8-Tetrahydro-8-oxonaphthalen-2-yl)benzamide
(5b, C17H15NO2)
Yield 186 mg (70%), recrystallization from ethanol. M.p.
P
P
a
b
c
R = ||Fo| - |Fc||/ |Fo|
P
P
1
wR2 = { [w(F2o - F2c)2]/ [w(F2o)2]}1/2
S = { [(F2o - Fc2)2]/(n/p)}1/2, where n is the number of reflections
137–140 °C; H NMR (300 MHz, CDCl3): d = 2.14 (m,
P
2H, 6-CH2), 2.64 (m, 2H), 2.96 (m, 2H, 5-CH2 and 7-CH2),
7.30 (d, J = 8.1 Hz, 1H, 4-H), 7.53 (m, 3H, Ph), 7.91 (m,
2H, Ph), 7.96 (d, J = 2.4 Hz, 1H, 1-H), 8.24 (br s, 1H,
NH), 8.28 (dd, J1 = 8.1 Hz, J2 = 2.4 Hz, 1H, 3-H) ppm;
13C NMR (75.5 MHz, CDCl3): d = 23.2, 28.9, 38.8, 118.3,
126.2, 127.4, 128.4, 129.4, 131.6, 132.5, 134.7, 137.4,
and p is the total number of parameters refined
a full-matrix least-squares procedure based on F2 with
SHELXL-97 [62]. All non-hydrogen atoms were refined
anisotropically. All hydrogen atoms were readily located in
difference Fourier maps and were placed at calculated
positions and treated using the appropriate riding models.
In the crystal structure of 5c, atom C6 is disordered over
two positions in the ratio 0.81:0.19. The crystallographic
data are listed in Table 3. CCDC-851204 contains the
supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via http://www.ccdc.cam.ac.
uk/data_request/cif.
ꢀ
140.3, 166.1, 198.9 ppm; IR (KBr): m = 1,662, 1,603,
1,585, 1,532, 1,497, 1,352 cm-1; MS (ES?, TOF):
m/z = 266 (MH?); HRMS calcd for C17H16NO2 (MH?)
266.1181, found 266.1187.
N-(5,6,7,8-Tetrahydro-6-methyl-8-oxonaphthalen-2-yl)-
benzamide (5c, C18H17NO2)
Yield 195 mg (70%), recrystallization from petrol ether.
1
M.p. 189–191 °C; H NMR (300 MHz, CDCl3): d = 1.15
(d, J = 6.1 Hz, 3H, Me), 2.33 (m, 2H, CH2), 2.69 (m, 2H,
CH2), 2.99 (m, 1H, 6-H), 7.30 (d, J = 8.4 Hz, 1H, 4-H),
7.54 (m, 3H, Ph), 7.89 (m, 3H, 1-H and Ph), 8.03 (br s, 1H,
NH), 8.25 (dd, J1 = 8.4 Hz, J2 = 2.4 Hz, 1H, 3-H) ppm;
13C NMR (75.5 MHz, CDCl3): d = 21.3, 30.5, 37.4, 46.9,
188.0, 126.2, 127.3, 128.6, 129.7, 131.8, 132.4, 134.8,
General procedure for the synthesis of 5a–5g
A mixture of the starting fused pyran-2-one 1 (1 mmol),
2 cm3 ethyl vinyl ether (2), 16.8 mg DABCO (15 mol%),
and 300 mg n-butanol in a sealed vial (10 cm3) was irra-
diated in the focused microwave equipment for the time
specified (Table 1). The final temperature was set to
140 °C (for 5a–5c), 150 °C (for 5e), 170 °C (for 5d), or
180 °C (for 5f, 5g), the power was set to 300 W, and the
ramp time to 5 min. Thereafter, the reaction mixture was
cooled, volatile components were removed in vacuo, the
remaining solid was treated with i-Pr2O and cooled. The
ꢀ
137.2, 139.8, 166.0, 198.7 ppm; IR (KBr): m = 3,348,
1,660, 1,605, 1,586, 1,532, 1,497, 1,452 cm-1; MS (ES?,
TOF): m/z = 280 (MH?), 302 (MNa?).
N-(5,6,7,8-Tetrahydro-6,6-dimethyl-8-oxonaphthalen-2-
yl)benzamide (5d, C19H19NO2)
Yield after column chromatography (Rf = 0.31; PE:A-
cOEt = 3:1): 182 mg (62%), recrystallization from
123

ˇ
A. Juranovic et al.
776
1
Acknowledgments We are grateful to the Ministry of Higher
Education, Science and Technology of the Republic of Slovenia and
the Slovenian Research Agency for financial support (grant nos. P1-
ethanol. M.p. 242–244 °C; H NMR (300 MHz, DMSO-
d6): d = 1.02 (s, 6H, 2 9 Me), 2.50 (s, 2H, CH2), 2.84 (s,
2H, CH2), 7.33 (d, J = 8.4 Hz, 1H, 4-H), 7.57 (m, 3H,
Ph), 7.98 (m, 3H, 3-H and Ph), 8.29 (d, J = 2.1 Hz, 1H,
1-H), 10.4 (br s, 1H, NH) ppm; 13C NMR (75.5 MHz,
DMSO-d6): d = 27.7, 33.5, 42.0, 51.7, 117.3, 125.8,
127.6, 128.3, 129.7, 131.4, 131.6, 134.6, 137.6, 137.9,
ˇ
0230-0103 and P1-0230-0175). Dr. B. Kralj and Dr. D. Zigon (Center
ˇ
for Mass Spectroscopy, Jozef Stefan Institute, Ljubljana, Slovenia)
are gratefully acknowledged for the mass measurements. This work
was also partially supported by the infrastructure of the EN–FIST,
Center of Excellence, Ljubljana, Slovenia.
ꢀ
165.5, 197.5 ppm; IR (KBr): m = 3,331, 1,664, 1,603,
1,531, 1,495, 1,306 cm-1; MS (ES?, TOF): m/z = 294
(MH?); HRMS calcd for C19H20NO2 (MH?) 294.1494,
found 294.1498.
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1
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ˇ
ˇ
tt, J = 7.4 Hz, 2H, 2-CH2), 2.89 (t, J = 7.4 Hz, 2H), 2.93
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s, 1H, 4-H), 7.77 (br s, 1H, NH), 7.86 (m, 2H, Ph) ppm; 13
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8. Kim ES, Kim KH, Kim SH, Kim JN (2009) Tetrahedron Lett
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NMR (75.5 MHz, CDCl3): d = 25.6, 32.4, 33.0, 116.8,
118.5, 124.5, 127.0, 128.7, 131.6, 135.2, 136.0, 140.6,
ꢀ
145.2, 165.7 ppm; IR (KBr): m = 1,643, 1,599, 1,578,
1,540, 1,492 cm-1; MS (ES?, TOF): m/z = 238 (MH?);
HRMS calcd for C16H16NO (MH?) 238.1226, found
238.1229.
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ˇ
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11. Stefane B, Perdih A, Pevec A, Solmajer T, Kocevar M (2010) Eur
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13. Kranjc K, Kocevar M, Iosif F, Coman SM, Parvulescu VI, Genin
N-(6,7,8,9-Tetrahydro-5H-benzo[7]annulen-2-yl)-
benzamide (5f, C18H19NO)
Yield 186 mg (70%), recrystallization from ethanol. M.p.
ˇ
E, Genet JP, Michelet V (2006) Synlett 1075
ˆ
14. Kranjc K, Kocevar M (2007) Bull Chem Soc Jpn 80:2001
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15. Nelson HM, Stoltz BM (2008) Org Lett 10:25
1
165–168 °C; H NMR (500 MHz, CDCl3): d = 1.64 (m,
ˇ
16. Kranjc K, Perdih F, Kocevar M (2009) J Org Chem 74:6303
4H, 2 9 CH2), 1.83 (m, 2H, CH2), 2.77 (m, 4H, 2 9 CH2),
7.08 (d, J = 8.0 Hz, 1H, 4-H), 7.35 (dd, J1 = 8.0 Hz,
J2 = 2.0 Hz, 1H, 3-H), 7.39 (d, J = 2.0 Hz, 1H, 1-H), 7.50
(m, 3H, Ph), 7.80 (br s, 1H, NH), 7.85 (m, 2H, Ph) ppm;
13C NMR (75.5 MHz, CDCl3): d = 28.2, 28.4, 32.6, 36.1,
36.7, 117.7, 121.0, 127.0, 128.6, 129.4, 131.5, 135.1,
17. Fischer TCM, Leisch HG, Mihovilovic MD (2010) Monatsh
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´
´
18. Guevara-Salazar JA, Quintana-Zavala D, Jimenez-Vazquez HA,
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ꢀ
135.7, 139.9, 144.2, 165.6 ppm; IR (KBr):m = 3,260,
2,916, 2,847, 1,645, 1,601, 1,600, 1,594, 1,579, 1,531,
Appl Chem 68:113
1,501 cm-1; MS (ES?, TOF): m/z = 266 (MH?).
22. Posner GH, Dai H, Bull DS, Lee JK, Eydoux F, Ishihara Y,
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N-(5,6,7,8,9,10-Hexahydrobenzo[8]annulen-2-yl)-
benzamide (5g, C19H21NO)
Yield 181 mg (65%), recrystallization from ethanol. M.p.
1
134–137 °C; H NMR (300 MHz, CDCl3): d = 1.35 (m,
4H, 2 9 CH2), 1.65 (m, 4H, 2 9 CH2), 2.71 (m, 4H,
´
´
25. Balasz L, Kadas I, Toke L (2000) Tetrahedron Lett 41:7583
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}
27. Kim WS, Kim HJ, Cho CG (2002) Tetrahedron Lett 43:9015
´
2 9 CH2), 7.05 (d, J = 7.8 Hz, 1H, 4-H), 7.45 (m, 5H,
1-H, 3-H, Ph), 7.84 (m, 2H, Ph), 7.99 (s, 1H, NH) ppm; 13
28. Leonard MS, Carroll PJ, Joullie MM (2004) J Org Chem 69:2526
C
29. Afarinkia K, Bearpark MJ, Ndibwami A (2005) J Org Chem
70:1122
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NMR (75.5 MHz, CDCl3): d = 25.8, 25.9, 31.8, 32.1,
32.2, 32.3, 118.2, 120.7, 127.0, 128.6, 129.5, 131.5, 135.1,
ˇ
31. Kranjc K, Kocevar M (2008) Synlett 2613
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33. Afarinkia K, Abdullahi MH, Scrowen IJ (2010) Org Lett 12:5564
ꢀ
136.0, 137.7, 142.0, 165.6 ppm; IR (KBr): m = 3,287,
2,916, 2,845, 1,651, 1,615, 1,603, 1,592, 1,580, 1,537,
ˇ
ˇ
1,499 cm-1; MS (ES?, TOF): m/z = 280 (MH?).
123

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123